Ketones in physics

7/28/2019 Ketones in physics

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C H A P T E R 1 4K e t o n e sSolvent-Induced Frequency ShiftsSolute-Solvent Interaction Affected by Steric FactorsInductive, Resonance, and Temperature EffectsOther Chemical and Physical EffectsOther Conjugated Carbonyl Containing CompoundsChalconesIntramolecular Hydrogen BondingCycloalkanonesSubstituted 1,4-BenzoquinonesConcentration EffectsReferencesFigures TablesFigure 14-1 301 (288)Figure 14-2 302 (290)Figure 14-3 303 (290)Figure 14-4 303 (291)Figure 14-5 304 (295)Figure 14-6 305 (296)Figure 14-7 306 (296)Figure 14-8 307 (296)Figure 14-9 308 (297)Figure 14-10 308 (297)Figure 14-11 309 (297)Figure 14-12 309 (298)Figure 14-13 310 (298)

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*Numbers in parentheses indicate in-text page reference.

288289290291291294294295297299299

14-114-214-2a14-314-3a14-3b14-3c14-414-514-614-714-7a1 4 - 814-914-1014-1114-1214-1314-1414-1514-1614-1714-1814-19

311312313314315315316316317318319320321322323324325326327328328329329330

(288)(288)(288)(288)(289)(290)(290)(290)(290)(291)(294)(294)(294)(295)(295)(296)(298)(298)(298)(298)(298)(298)(298)(299)

287


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2 8 8 K e t o n e sA c e t o n e i s t h e s i m p l e s t m e m b e r o f t h e k e t o n e s e r ie s . I ts e m p i r ic a l s t r u c t u r e i s

C H 3 - C ( = O ) - C H 3. T a b le 1 4.1 l is t s IR a n d R a m a n d a t a f o r a c e t o n e a n d a c e t o n e - d 6 ( 1 ,2 ) . T h eC D 3 fr e q u e n c ie s a n d a s s i g n m e n t s a re l is t e d d i r e c t ly u n d e r t h o s e f o r t h e C H 3 fr e q u e n c ie s a n dass ign me n t s . The f r equ ency r a t io s f o r CH3/C D 3 va ry be tw een 1 .11 and 1 .38 . The B 1 a n d B2 CH 3rock ing m od e to CD 3 rock ing m od e f r eq uen cy r a t io s a r e 1 . 132 and 1 . 108 , re spec t ive ly , and th i si n d i c a t e s t h a t t h e s e t w o m o d e s a r e c o u p l e d w i t h B 1 a n d B2 modes , r e spec t ive ly . The se da tei l lu s t r a te t h a t b o t h I R a n d R a m a n d a t a a n d d e u t e r a t e d a n a l o g s a re r e q u i r e d t o m a k e d e t a il e da s s i g n m e n t s o f m o l e c u l a r c o m p o u n d s .

S O L V E N T - I N D U C E D F R E Q U E N C Y S H I F T SH a l l a m h a s r e v i e w e d t h e li t e r at u r e c o n c e r n i n g a t t e m p t s t o d e v e l o p a n a c c u r a t e q u a n t i t a t iv e a n dp h y s i c a l m e a n i n g f u l e x p l a n a t i o n o f s o l v e n t - i n d u c e d s t r e t c h i n g f r e q u e n c ie s ( 3 ). K i r k w o o d e t a l .(4 ) and Baue r and Mago t (5 ) r e l a t ed the obse rved f r equency sh i f t s and the d i e l e c t r i c cons tan t e o ft h e s o l v e n t . T h e ( K ) i r k w o o d ( B ) a u e r ( M ) a g o t w o r k r e s u l t e d i n t h e K B M e q u a t i o n :

( V v a p o r - - V s o l u t i o n / V V a p o r = A v / v = C [ ( e , - 1)/(2 e + 1)]J o s i e n a n d F u s o n r e f in e d t h e e q u a t i o n t o i n c lu d e a t e r m b a s e d o n t h e i n d e x o f re f r a ct i o n o f th eso lven t (6 ) . Be l l amy e t a l . f o u n d t h a t A v / v f o r a n y s o l u t e p l o t t e d v s ( A v / v ) f o r a n y o t h e r s o l v e n tw i t h i n a c la s s o f c o m p o u n d s p r o d u c e d a li n e a r cu r v e ( 7 ). T h e y t h e r e f o r e p r e d i c t e d t h a t g r o u pf r equency sh i f t s we re loca l a s soc ia t ion e f f e c t s be tween so lu t e and so lven t and no t d i e l e c t r i cef fects . Be l lamy e t a l . p r o p o s e d t h a t v h e x a n e s h o u l d b e s u b s t i t u t e d f o r v v a p o r i n t h e K B Mequa t ion in o rde r t o nega te the e f fe c t s o f phase chang e (7 ) . Tab le 14 .2 i llu s t r a t e s the ap p l ica t ionof the KBM equa t ion u s ing IR da ta f o r ace tone vC=O f r equenc ie s in va r ious so lven t s . Tab le 14 . 2s h o w s t h a t t he K B M e q u a t io n p r e d ic t s t h e v C = O m o d e w i t h i n - 2 . 1 t o + 1 4 . 3 c m - 1 . The be s t f i ti s f o r ace tone in so lu t ion w i th ace ton i t r i l e and the wor s t f i t i s f o r ace tone in wa te r . I n the case o fC H C 13 a n d t h e f o u r a l co h o l s , t h e v C = O f r e q u e n c y d i ff e re n c e s b e t w e e n t h e c a l c ul a t e d a n do b s e r v e d r a n g e a r e b e t w e e n 4 . 3 a n d 7 .7 c m - 1 . T h e l a r g e r d i ff e r en c e s h e r e c o m p a r e d t o t h e o t h e rs o l v e n t s a re m o s t l ik e l y t h e re s u l t o f i n t e r m o l e c u l a r h y d r o g e n b o n d i n g ( C = O . . . H C C 1 3 o rC = O . . . H O R ) .

T a b le 1 4 . 2a c o n t a i n s t h e c a l c u la t e d v a lu e s f o r A - 1 / 2 A + 1 a n d X - Y / X w h e r e A a n d Y a r eequa l t o 0 to 85 and X equa ls 85 ( se e the K BM equa t ion ) . The s e two s e t s o f da ta a r e p lo t t e d inF ig . 1 4 .1 . T h e s e d a t a s h o w t h a t a n y s e t o f n u m b e r s u s i n g t h e e q u i v a l e n t o f t he K B M e q u a t i o n o rBe l l amy 's p ropos a l y i e ld s a ma the ma t ica l cu rve . I n pa r t icu la r , the l i nea r p lo t X -Y vs Y i s thusm e a n i n g l e s s i n p r e d i c t i n g v C - - O f r e q u e n c i e s ( 8 ) . I n t e r m o l e c u l a r h y d r o g e n b o n d i n g a n d d i p o l a rin t e r ac t ion be tween so lu t e and so lven t a s we l l a s d i e l e c t r i c e f f e c t s mus t p lay a r o l e in the vC=Of r e q u e n c ie s o f c a r b o n y l c o n t a i n i n g c o m p o u n d s . S t er ic f a ct o r s , w h i c h a l so p l a y a r o l e b e t w e e ns o l u t e - s o l v e n t i n t e r a c t i o n , m u s t a l s o b e c o n s i d e r e d i n p r e d i c t i n g v C - - O f r e q u e n c i e s i n a n ypar t i cu la r phys ica l phase ( se e in wha t f o l lows) .Tab le 14 . 3 l i s t s the C=O s t r e t ch ing f r equenc ie s f o r a l ipha t i c ke tone s in the vapor phase andi n 1 % w t . / v o l , i n v a r i o u s s o l v e n t s (9 ) .

I n t h i s s e ri e s o f k e t o n e s ( d i m e t h y l k e t o n e t h r o u g h d i - t e r t - b u t y l k e t o n e ) t h e s t e ri c f ac t o r o f t h ea lky l g roup( s ) and the bas ic i ty o f the ca rbony l g roup bo th inc r ease . As the s t e r i c f ac to r o f thea l k y l g r o u p i n c r e a s e s t h e i n t e r m o l e c u l a r d i s t a n c e b e t w e e n t h e c a r b o n y l g r o u p a n d a s o l v e n t


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Variables in Data Interpretation 2 8 9molecu l e i nc r ease s . I n t he case o f i n t e rmolecu la r hydro gen bo nd ing be twe en a so lven t and ap ro to n an d a ca rbony l g roup , t he s t r eng th o f t he hydrogen bo nd depen ds upo n a t le a s t f ou rfactors . These are , the bas ic i ty of the carbonyl group, the acidi ty of the solvent proton, the s te r icfactor of the dialkyl groups of the dialkyl ke tone , and the s te r ic factor of the a toms or groups ofthe so lven t molecu l e s no t i nvo lved d i r ec t ly wi th the i n t e rmolecu la r hydrogen bond .

Al l o f t he a l ipha t i c ke tone s exh ib i t t he i r vC=O mode a t i t s h ighe s t f r equency i n t he vaporphase (1699-1742cm-1) . I n so lu t i on , t he h ighe s t vC~O f r equenc i e s a r e exh ib i t ed i n hexaneso lu t i on (1690 .3 -1727 .2 c m - 1 ) . W ith the excep t i on o f d ime thy l ke ton e ( ace tone ) i n hexane , t hevC- -O f r equency f o r t he o the r d i a lky l ke tone s dec r ease s i n f r equency wi th i nc r eas ing nega t ivevalues for bo th a* ( increa s ing e lect ro n re lease to the carbon yl group ) an d E s (an increas ing s te r icf ac to r o f t he a lky l g roup) and the s umm at ion o f cr* t imes the s um mat io n o f E s 9 10 -2.

I n the case o f d ime thy l ke tone , i t s vC ~O mo de occur s a t a h ighe r f r equency than v C -O fo rme thy l e thy l ke tone on ly i n t he f o l l owing so lven t s , t e r t - bu ty l a l coho l , ch lo ro fo rm, i sopropy la l coho l , e thy l a l coho l , and me thy l a l coho l . I n t he se so lven t s t he r e i s i n t e rmolecu la r hydrogenb o n d i n g b e t w e e n s o l u t e a n d s o l v e n t ( C ~ O . . . H O R a n d C - O . . . H C C 1 3 ) . M o r e o v e r , i n t h e s epro t i c so lven t s t he vC =O f r equency o rde r fo r me thy l e thy l ke ton e an d d i e thy l ke tone i s reve r sedf rom the s equence tha t t hey exh ib i t when the se d i a lky l ke tone s a r e i n t he o the r so lven t s .

S O L U T E - S O L V E N T I N T E R A C T I O N A F F E C T E D B Y S T E R I CF A C T O R STable 14 .3a shows a compar i son o f t he ca rbony l s t r e t ch ing f r equency d i f f e r ence f o r ke tone s i nhexane s o lu t i on an d i n e ach o f t he o the r so lven t s ( 9 ) . The s t r eng th o f an i n t e rmo lecu la rhydrogen bond (C- -O. . .HOR or C- -O. . -HCC13) i s p ropor t i ona l t o t h i s f r equency d i f f e r ence .The l a rge r t h is f r equency d i ff e rence , t he s t r onge r t he i n t e rm olecu la r hyd rogen bond . Or , i n o the rwords , t he s t r onge r t he i n t e rmolecu la r hydrogen bond be tween the ke tone so lu t e and the p ro t i cso lven t , t he more vC- -O sh i f t s t o l owe r f r equency when compared t o vC-O fo r t he same ke tonein n -hexan e so lu t i on . The mo s t ac id p ro ton f o r t he a l coho l s e ri e s is t ha t f o r me thy l a lcoho l , andthe leas t acidic proto n i s that for te r t -butyl a lcohol . In addi t ion, the s te r ic factor is the larges t fort e r t - bu ty l a l coho l , and the l e ast f o r me thy l a l coho l . The m os t bas i c ke tone ca rbony l g roup i s i nthe case of d i - te r t -butyl ke to ne and the leas t bas ic carbony l group i s in the case of d im ethy lke tone . Neg lec t i ng s t e r i c f ac to r s , t he se f ac t s wou ld p r ed ic t t ha t t he s t r onge s t i n t e rmolecu la rhydrogen bonds wou ld be f o rmed be tween me thy l a l coho l and d i - t e r t - bu ty l ke tone , and theweake s t be tw een t e r t - bu ty l a lcoho l , and d im e thy l ke tone . S tudy o f Tab le 14 .3a shows tha t t hes t r onge s t i n t e rmolecu la r hydrogen i s ac tua l ly f o rmed be tween me thy l a l coho l and d i i sopropy lke tone , and the s t r eng th o f t he i n t e rmolecu la r hydrogen bond wi th d i i sopropy l ke tone dec r ease sin the order methyl a lcohol , e thyl a lcohol , i sopropyl a lcohol , and te r t -butyl a lcohol . The s t rengthof t he i n t e rmolecu la r hydrogen bond f o rmed be tween d i i sopropy l ke tone and ch lo ro fo rm f a l l sbe tween tha t f o r t e r t - bu ty l a l coho l and i sopropy l a l coho l . I n t he a l coho l s e r i e s , t he s t r eng th o fthe i n t e rmolecu la r hydrogen i s a l so s t r onge r be tween d i i sopropy l ke tone than be tween d i - t e r t -bu ty l ke tone . The s t r eng th o f t he i n t e rmolecu la r hydrogen bond i s l e s s i n t he case o f e thy li sopropy l ke tone com pared t o d i i sopropy l ke tone , bu t i t a lso i s s t r onge r t han i n t he case o f d i -t e r t - bu ty l ke tone . The se da t a show tha t s t e r ic fac to rs inc r ease the C - O . . .H in t e rmo lecu la r


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290 Ketonesh y d r o g e n b o n d d i st a n ce , t h u s w e a k e n i n g t h e p o s s ib l e s t r e n g t h o f t h is i n t e r m o l e c u l a r h y d r o g e nb o n d .

Th e k e t one v C=O f req u ency sh i f t s i n nonp ro t i c s o l v en t s a re a l so l e s s i n t h e ca s e o f d i - t e r t -b u ty l k e t o ne v s t h e o th e r d i a lk y l k e t ones . Th ere fo re , s t e r i c f ac to r s o f t h e a lk y l g rou p s a l so p l ay aro l e i n t h e d i e l ec t r i c e f f ec t s o f t h e so lv en t u p on t h e ca rb ony l g rou p .

Tab l e 1 4 .3 b sh ows a comp ar i son o f t h e ca rb ony l s t r e t ch ing f r eq u ency d i f f e rence fo r d i a lk y lk e t on es i n me th y l a l coh o l and o th e r p ro t i c s o lv en t s (9 ) . In t h i s ca s e , th e s t r en g th o f t h ei n t e r m o l e c u l a r h y d ro g e n b o n d ( C - - O - - .H ) d e c re a s e s a s th e n u m b e r i n cr e as e s . T h i s c o m p a r i s o nsh ows t h a t s t e r i c f ac t o r s a l so a f f ec t t h e s t r eng th o f t h e i n t e rmo l ecu l a r h y d rog en b ond .

Tab l e 1 4 .3 c sh ows a comp ar i son o f t h e d i f f e rences i n t h e ca rb ony l s t r e t ch ing f r eq u enc i e s o fd i a lk y l k e t ones i n h ex ane so lu t i on and i n a l coh o l s o l u t i on fo r s o lu t e mo l ecu l e s no t i n t e rmo-l ecu l ar l y h y d ro g en b o nd e d (9 ). Th ese d a t a sh o w th a t t h e f r eq u e ncy d i f fe rence d ec rea s es fo r th e s ek e t ones i n a l coh o l s o lu t i on , p rog res s i ng i n t h e s e r i e s me th y l a l coh o l t h rou g h t e r t -b u ty l a l coh o l .W i t h i n c re a s e d b r a n c h i n g o n t h e 0 ~- ca rb on a t o m o f th e C - O H g r o u p , t h e i n t e r m o l e c u l a r p o l a re f fec t d u e t o t h e a l coh o l ox y g en a t om i s d ec rea s ed ; t h u s , t h e re i s a le s s e r p o l a r e f fec t u p o n d i a lk y lk e t o n e c a r b o n y l g r o u p s s u r r o u n d e d b y i n t e r m o l e c u l a r l y h y d r o g e n - b o n d e d a l c o h o l m o l e c u l e sp rog res s i ng i n t h e s e r i e s me th y l a l coh o l t h rou g h t e r t -b u ty l a l coh o l . Th e v C=O mod e d ec rea s esi n f r eq u ency a s t h e p o l a r i t y o f t h e so l v en t i nc rea s es .

Tab l e 1 4 .4 l i s t s d a t a fo r t h e C=O s t r e t ch ing f r eq u enc i e s fo r n -b u ty rop h enone and t e r t -b u t y r o p h e n o n e i n 0 - 1 0 0 m o l % C H C 1 3/ CC 1 4 s o l u t i o n s ( 2 % w t . / v o l . ). T h e v C = O m o d e f o r b o t hn - b u t y r o p h e n o n e ( 1 6 9 1 - 1 6 8 2 . 6 c m - 1 ) a n d t e r t - b u t y r o p h e n o n e ( 1 6 7 8 .4 - 1 6 7 4 . 1 c m - 1 ) d e c re a s e si n f r eq u ency a s t h e m o l e % CHC1 3 /CC1 4 i s i nc rea s ed f rom 0 -1 0 0 cm -1 . Howe v er , it is no t e d t h a tt h e v C - - O f r e qu e n c y f o r n - t e r t - b u t y r o p h e n o n e d e c re a s e s i n f r e q u e n c y b y o n l y o n e - h a lf as m u c ha s th a t fo r n - bu t y r o p h e n o n e ( 4 . 3 c m - 1 / 9 c m - 1 = 0 .4 8 ) i n g o in g f ro m s o l u t io n i n C C 14 t oso lu t i on i n CHC13 . Th e C= O g rou p fo r t h e t e r t -b u ty ro ana l og i s mo re b a s ic t h an t h e n -b u ty roa n a l o g , a n d o n t h i s b a s i s o n e w o u l d e x p e c t a s t r o n g e r i n t e r m o l e c u l a r h y d r o g e n b o n d t o b efo rmed b e tween C=O. . .HCC1 3 fo r t h e t e r t -b u ty ro ana l og t h an fo r t h e n -b u ty ro ana l og , and i t i sno ted tha t th i s i s no t the case . The reason for th i s i s tha t the s t er ic effec t o f the t er t -bu tyro groupp rev en t s t h e C1 3 CH p ro t on f rom com i ng a s c l o se i n space t o t h e C= O ox y g en a t o m i n t h e ca s e o ft e r t - b u t y r o p h e n o n e , w h i c h p r e v e n t s i t f r o m f o r m i n g a s s t r o n g a C = O - - . H C C 1 3 b o n d a s i n t h eca se o f t h e n -b u ty ro ana log wh ere t h e n -b u ty ro g rou p h a s a l e s s e r s t e r i c f ac t o r .

F i g u r e 1 4 . 2 s h o w a p l o t o f t h e v C = O f r e q u e n c y f o r t e r t - b u t y r o p h e n o n e v s t h e m o l e %CHC1 3 /CC1 4 . Th e r e su l t i ng cu rv e i s non l i nea r d u e t o t h e fo rma t i on o f C=O. . .HCC1 3 h y d rog enb ond s . Th e g ene ra l d ec rea s e i n f r eq u ency i s d u e t o t h e d i e l ec t r i c e f f ec t s o f t h e so lv en t sy s t em.Th e ca rb ony l s t r e t ch ing f r eq u enc i e s fo r n - t e r t -b u ty rop h enone occu r a t l ower f r eq u enc i e s(1 6 7 8 .4 -1 6 7 4 .1 cm -1 ) com p ared t o t h o se fo r d i - te r t -b u ty l k e t on e (1 6 8 5 .9 -1 6 8 0 .7 cm -1 ) i n 0 -1 0 0 m o l% CHC1 3 /CC1 4 d u e t o con ju g a t i on o f t h e p h eny l g ro u p wi th t h e ca rb o ny l g rou p , wh ichw e a k e n s t h e C = O b o n d ( 1 0 ) .

I N D U C T I V E , R E S O N A N C E , A N D T E M P E R A T U R E E F F E C T STable 14 .5 li s t IR da ta for acetone, 0~-ch loroacetone, ace top hen on e, and b en zo phe no ne in CS 2s o l u t i o n b e t w e e n ~ 2 9 a n d - 1 0 0 ~ ( 1 1) . F i g u re 1 4 .3 s h o w s p l o t s o f t h e ca r b o n y l s t r e t c h in gf req u enc i e s fo r t h e s e fou r com p o u nd s v s t h e t emp e ra tu re o f t h e CS2 so l u t i o n in ~ Th ese p l o t s


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V a r i a b l e s i n D a t a I n t e r p r e t a t i o n 291s h o w t h a t a ll o f t h e v C - - O m o d e s d e c r e a se i n f r e q u e n c y a s t h e t e m p e r a t u r e i s l o w e r e d f r o m r o o mtemp e ra tu r e . Two vC- -O f r equen c ie s a r e no ted in the case o f 0~ - ch lo roace ton e , an d bo th o ccur a ta h ighe r f r eque ncy t han vC- -O fo r ace tone . The induc t ive e f fe c t o f an 0~-C1 a to m in c r ease s thevC- -O f r equency , and the induc t ive e f f e c t i s i ndependen t o f spa t i a l o r i en ta t ion . The re i s a f i e lde ff ec t o f a C1 a t o m n e a r i n s p a c e t o t h e c a r b o n y l o x y g e n a t o m , a n d i t a ls o c a u s e s t h e v C ~ O m o d eto inc r ease in f r equency . Thus , r o ta t iona l confo rmer I i s a s s igned to the h ighe r f r equency vC- -Oband , wh i l e r o ta t iona l confo rmer I I i s a s s igned to the lowe r f r equency vC~-O band in the case o f0 ~- ch lo r oa ce t on e . T h e c o n c e n t r a t i o n o f ro t a t i o n a l c o n f o r m e r I in c r e a s e s w h i l e t h e c o n c e n t r a t i o no f r o t a t i o n a l c o n f o r m e r I I d e c r ea s e s w i t h d e c r e as e i n t e m p e r a t u r e ( 1 1 ).

S u b s t i t u t io n o f o n e o r t w o p h e n y l g r o u p s f o r o n e o r t w o m e t h y l g r o u p s o f a c e t o n e y i e l d sa c e t o p h e n o n e ( v C - - O , 1 6 8 9 . 4 c m - 1 ) a n d b e n z o p h e n o n e ( v C - - O , 1 6 6 3 . 3 c m - 1 ) , r e s pe c ti v el y.Thus , the f i r s t pheny l g roup cause s vC- -O to dec r ease in f r equency by 28 . 1 c m - 1 whi le thes e c o n d p h e n y l g r o u p c a u s e s v C - - O t o d e c r e a s e i n f r e q u e n c y b y a n a d d i t i o n a l 2 6 . 1 c m - 1 . T h ep h e n y l g r o u p ( s ) i s ( a r e ) c o n j u g a t e d w i t h t h e c a r b o n y l g r o u p , a n d i t w e a k e n s t h e C - - O b o n d ,which cause s i t s vC- -O mode to v ib ra t e a t l owe r f r equency .

O T H E R C H E M I C A L A N D P H Y S I C A L E F F E C T ST a bl e 1 4. 6 s h o w s a c o m p a r i s o n o f t h e v C - - O f r e q u e n c ie s f o r 2 % w t . / v o l , k e t o n e i n 0 - 1 0 0 m o 1 %(CH3) 2 SO/CC14 s olu t io ns . F igure 14.4 sho ws plot s of vC--- -O vs m ole % (CH3) 2 SO/CC14 for thesame s ix ke ton e s a s sho wn in Tab le 14 .6 . A l l s ix cu rve s dec r ease in f r equ enc y in a l i nea r ma nn e ras mo le % (CH3) 2 S O/CC14 i s i nc r eased f rom ~ 30 to 1 00 m o l% (CH3)2S O/CC14. Th i s i s i n theorde r o f the inc r eas ing po la r i ty o f the so lven t sy s t em . A ll s ix ke ton e s a ppear t o be a ff ec t ed in thesame ma nn e r be cause the l i nea r po r t io n o f the cu rve s i s pa ra l le l . The vC----O f r equenc ie s dec r easei n t h e o r d e r a c e t o n e , 2 , 4 , 6 - t r i m e t h y l a c e t o p h e n o n e , 4 - n i t r o a c e t o p h e n o n e , a c e t o p h e n o n e , 4 -m e t h o x y a c e t o p h e n o n e , a n d b e n z o p h e n o n e . T h e e f fe c t o f c o n j u g a t i o n w a s d is c u s s e d p re v i o us l y .I n t h e c a s e o f 2 , 4 , 6 - t r i m e t h y l a c e t o p h e n o n e , t h e c a r b o n y l g r o u p a n d t h e p h e n y l g r o u p a r e n o tc o p l a n a r ; t h e r e f o r e , t h e C = O g r o u p i s n o t c o n j u g a t e d w i t h t h e p h e n y l g r o u p . T h u s , t h e C = Og r o u p i s h i g h e r i n f r e q u e n c y t h a n t h a t e x h i b i t e d b y a c e t o p h e n o n e b y 1 3 c m - 1 , b u t l o w e r i nf r e q u e n c y t h a n a c e t o n e b y 1 4 c m - 1 . H a m m e t t crp v a l ue s f o r 4 -n i t r o a n d 4 - m e t h o x y b e n z o p h e -none cause the vC~-O mode to be h ighe r and lowe r in f r equency , r e spec t ive ly , than vC- -O fo ra c e t o p h e n o n e .

O T H E R C O N J U G A T E D C A R B O N Y L C O N T A I N I N GC O M P O U N D SI t i s i n t e r e s t i n g t o c o n s i d e r t h e p o s s i b l e m o l e c u l a r c o n f i g u r a t i o n s o f c o n j u g a t e d c a r b o n y lc o n t a i n i n g c o m p o u n d s . L i n - V i e n e t a l . ( 1 3 ) h a v e r e v i e w e d t h e p u b l i s h e d s t u d i e s o f t h e s ec o m p o u n d s ( 1 4 ), a n d t h e y r e p o r t t h a t a p l a n a r c o m p o u n d s u c h a s 3 - b u t e n - 2 - o n e e x i s t s i n s - tr a n s


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2 9 2 Ketonesa n d s - c is c o n f i g u r a t i o n s i n C C 1 4 s o l u t i o n . T h e s e t w o c o n f o r m e r s f o r 3 - b u t e n - 2 - o n e a r ei l l u s t r a t ed he re :

0

s - t m n s s - c i sCC1_4soln , (c rn "1) CC l~ so ln . (c rn "1)C = O s t r e t c h in a C = O s tr et ch in _ a1 6 8 7 v s 1 7 0 7 v s,C = C s t r e tc h i n a C = C s t r e tc h i n a1 6 4 8 w 1 6 1 8 m , s h( C = O s t r . ) - ( C = C s t r , ) ( C = O s t r . ) - ( C = C str.)3 9 8 9

T h e s e t w o c o n f o r m e r s r e s u l t f r o m 1 8 0 ~ r o t a t io n o f t he C = C g r o u p a b o u t t h e C 2 - C 3 s in g l eb o n d . T h i s n o t a t i o n a d e q u a t e ly d e s c r ib e s t h e m o l e c u l a r co n f i g u r at i o n s i n t h e f o r e m e n t i o n e d c a s e( 1 3 - 1 5 ) .

I n t h e v a p o r p h a s e t h e C = O s tr . a n d C = C s tr . f r e q u e n c i e s a re a s s ig n e d a t 1 7 1 5 a n d1627 c m - 1 , r e s p e c t i v e l y ( 1 6 ) . T h e f r e q u e n c y s e p a r a t i o n b e t w e e n t h e s e t w o m o d e s i s 8 8 c m - 1 .C o r r e s p o n d i n g m o d e s f o r t h e s - t r a n s i s o m e r a r e n o t d e t e c t e d i n t h e v a p o r p h a s e a t e l e v a t e dt e m p e r a t u r e . T h e r e f o r e , 3 - b u t e n e - 2 - o n e e x i s t s o n l y a s t h e s - c i s c o n f o r m e r a t e l e v a t e d t e m p e r a -t u r e i n t h e v a p o r p h a s e . T h e I R b a n d s a t 9 8 6 a n d 9 5 1 c m - 1 c o n f i r m t he p r e s e n ce o f th e C H = C H 2g r o u p .

S i m i l a r l y , a c o m p o u n d s u c h a s 3 - m e t h y l - 3 - b u t e n - 2 - o n e c a n a l s o b e a d e q u a t e l y d e f i n e d a ss - t r a n s a n d s - c i s c o n f o r m e r s a s i l l u s t r a t e d h e r e :

O O

H -C ~ \H H

I n t h e v a p o r p h a s e a t e le v a t e d t e m p e r a t u r e t h e I R b an d s a t 1 7 0 0 c m - 1 a n d 1 6 3 9 c m - 1 a r ea s s ig n e d t o C - O s t r e t ch i n g a n d C = C s t r e tc h i n g , re s p e c ti v e ly ( 1 6 ). T h e f r e q u e n c y s e p a r a ti o nb e t w e e n t h e s e t w o m o d e s i s 6 1 c m - 1 . T h e r e f o r e , 3 - m e t h y l - 3 - b u t e n - 2 - o n e e x i s t s o n l y a s t h e s - c i sc o n f o r m e r i n t h e v a p o r - p h a s e a t e le v a t e d t e m p e r a t u r e . T h e I R b a n d a t 9 2 9 c m - 1 c o n f i r m s t h ep r e s e n c e o f t h e C = C H 2 g r o u p .


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Variables in Data Interpretation 293L e t u s n o w c o n s i d e r t h e n u m b e r o f p o s s ib l e c o n f o r m e r s f o r 4 - m e t h y l - 3 -b u t e n - 2 - o n e "

. / \H3 C X X H C H 3 H C H ,H C H 3s-trans s-trans s-cis s-cis[s-trans, cis CH3] [s-trans, trans CH3] [s-c is , c is CH3] [s-c is , t rans CHa]

H e r e w e n o t e t h a t s - t r a n s a n d s - ci s d o n o t d e f i n e t h e s p a t ia l p o s i t i o n o f t h e C H 3 g r o u p .T h e r e f o r e , t h e a d d i t i o n a l t e r m t r a n s C H 3 a n d c is C H 3 m u s t b e u s e d t o a d e q u a t e l y s p e c if y e a c h o ft h e f o u r p o s s ib l e c o n f o r m e r s f o r 4 - m e t h y l - 3 - b u t e n - 2 - o n e a s s h o w n i n b r ac k e t s i n t h e c o n f o r m e r ss h o w n h e re .

T h e C - - O a n d C = C s t r e t ch i n g f r e q u e n c ie s f o r 4 -m e t h y l - 3 - b u t e n - 2 - o n e i n C C I 4 s o l u t i o n a r eg i v e n h e r e :

. s -t rans conformer (cm ~ )C=O s t r. (vs ) C=C s t r. (m,sh)1 6 7 4 1 6 54

( C = O s t r . )- ( C = C s t r, .) ( c m 1 )2 9

s-cis c onfo rmer (cm 1)C= O s t r . (s ) C= Cs tr . (s )1 6 9 2 1 6 3 2 6 0T h e s e d a t a s u p p o r t o n l y t h e p r e s e n c e o f t h e s - ci s o r s - t ra n s p a r t o f th e c o n f o r m e r . N M R d a t a

a r e n e e d e d t o h e l p e s t a b l i s h t h e p r e s e n c e o f a c is o r t r a n s C H 3 g r o u p , a n d t h e s e d a t a w e r e n o ta va il ab le . S im i la r c o m p o u n d s c o n t a i n i n g t h e t r a n s C H = C H g r o u p e x h i b i t a w e a k - m e d i u m b a n di n t h e r e g i o n 9 7 4 - 9 8 0 c m - 1 .

A s a l re a d y s h o w n , t h e C = C a n d C = O s t r e t ch i n g f r e q u e n ci e s f o r s -c is a n d s - t ra n s c o n f o r m e r sa r e v e r y d if f e re n t . T h e q u e s t i o n t o a n s w e r i s w h y t h e y a r e d if f e re n t . I t is p o s s i b le t h a t i n o n e c a s et h e C = C a n d C = O s t r e t ch i n g v ib r a t io n s c o u p l e i n t o i n - ph a s e a n d o u t - o f - p h a s e s t re t c h i n g m o d e si n o n e c o n f o r m e r a n d n o t i n t h e c as e o f t h e o t h e r c o n f o r m e r .

I n t h e c as e o f 3 - m e t h y l - l , 3 - p e n t a d i e n e t h e t w o C = O C - C = C g r o u p s ar e c o u p l e d i n t o an i n -p h a s e ( C = C ) 2 v i b r a t i o n a n d a n o u t - o f - p h a s e ( C = C ) 2 v i b r a t i o n a s d e p i c t e d h e r e :

. ?H3CH3

H Hin -p h a se (C = C )2 s t r . o u t -o f -p h ase (C = C )2 s t r .

I n t h e ca s e o f 3 - m e t h y l - l , 3 - p e n t a d i e n e , t h e i n - p h a s e s t r . m o d e o c c u r s a t 1 65 0 c m - 1 a n d t h eo u t - o f - p h a s e s t r . m o d e o c c u r s a t 1 6 1 0 c m - 1 i n t h e v a p o r p h a s e . I n c as e s s u c h a s 2 - m e t h y l - 2 -p e n t e n e a n d 2 , 4 , 4 -t r i m e t h y l - 2 -p e n t e n e t h e C = C b o n d is n o t c o n j u g a t e d a n d t h e C = C s t r e t ch i n gm o d e o c c u r s a t 1 6 6 5 a n d 1 6 5 8 c m - 1 , r e s p e ct iv e l y . T h e r e fo r e , i t a p p e a r s t h a t t h e i n - p h a s e ( C = C ) 2s t r e t c h i n g v i b r a t i o n o c c u r s n e a r t h a t e x p e c t e d f o r i s o l a t e d C = C s t r e t c h i n g v i b r a t i o n s w h i l e t h eo u t - o f -p h a s e ( C = C ) 2 s t r e t ch i n g v i b r at i o n s o c c u r c o n s i d e r a b ly l o w e r t h a n i s o la t e d C = C s t re t c h -i n g v i b r a t i o n s .


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294 KetonesT h e s a m e b e h a vi o r fo r th e C = O a n d C - C s t r e t c hi n g m o d e s w a s a lr e a d y n o t e d h e r e f o r th e s -

c i s con fo rmers . Th e C=O s t r . mod e occu r red a t a f r eq u ency ex p ec t ed fo r a con j u g a t ed ca rb ony lc o n t a i n i n g c o m p o u n d , w h i le t h e C = C s tr . m o d e o c c u r r e d a t a lo w e r f r e q u e n c y t h a n e x p e c t e d f o ran i s o l a t ed C-C d ou b l e b ond . On t h e o th e r h and , t h e s - t r an s con fo rmers ex h ib i t ed f r eq u enc i e sf o r C = O a n d C = C s t r e t ch i n g e x p e c te d f o r c o n j u g a te d c a r b o n y l c o n t a i n i n g c o m p o u n d s w h i le t h eC=C s t r e t ch ing f r eq u ency occu r red a t f r eq u enc i e s comp arab l e t o t h o se ex h i b i t ed b y comp ou nd scon t a i n i ng i s o l a t ed t r an s CH--CH g rou p s . On t h i s b a s i s , we b e l i ev e t h a t t h e s e mod es a re b es td esc r i b ed a s i n -p h ase and ou t -o f -p h ase C- -C-C--O s t r e t ch i ng v i b ra t i on s i n t h e ca s e o f t h e s -c i scon fo rm ers , and a s C= O and C - -C s t r e t ch ing mo d es i n t h e ca s e o f t h e s - tr an s con fo rm ers .C o m p o u n d s s u c h a s 3 - m e t h y l - 4 - p h e n y l - 3 - b u t e n - 2 - o n e a n d ~ - h e x y l c i n n a m a l d e h y d e c o n t a i n t h eC--C H g rou p , an d we a re on ly abl e t o e s t ab l ish t h a t t h ey a re in t h e s -ci s con f ig u ra t i on . Th e c is[H , C H 3 ] and c i s [H, C 6 H l l ] a r e one o f t h e two p os s ib il it i e s fo r t h e s e two co mp o u nd s . Th eb and s i n t h e r eg i on 8 6 7 -8 7 0 cm -1 su p p o r t t h e p re s e nce o f t h e C- -C H g rou p .

Table 14 .7 a lso l i s ts IR vapor -phase da ta for cha lcone and i t s der iva t ives . The IR da ta i sr eco rd e d a t e lev a t ed t emp e ra tu re , and a ll o f t h e d a t a ind i ca t e t h a t t h e s e co mp ou n d s ex i s t on l y ast h e s -c i s , t r an s CH=CH con fo rmer .

C H A L C O N E SCh a lcones h av e t h e fo l l owing emp i r i ca l p l ana r s t ru c tu re :

o H

Th e p h eny l g rou p o f t h e s t y ry l g rou p i s nu mb ered 2 t h rou g h 6 , and t h e p h eny l g rou p o f t h eb enzoy l g rou p i s nu mb ered 2 ' t h rou g h 6 ' . Su b s t i t u t i on i n t h e 2 ,6 -p os i t i on s wi th C1 2 o r ( C H 3 ) 2wou ld s t e r i ca l l y p rev en t t h e s t y ry l p h eny l g rou p f rom b e ing cop l ana r wi th t h e r e s t o f t h emolecule . Moreover , subs t i tu t ion of C12 o r ( C H 3 ) 2 i n t h e ~ ,2 -p os it i on s on t h e s t y ry l g rou p w ou lda lso s t e r i ca l ly p rev en t t h e s t y ry l p h en y l g rou p f rom b e i ng co p l ana r wi th t h e r e s t o f th e m o l ecu l e .Subs t i tu t ion of C12 o r ( C H 3 ) 2 i n t h e 2 ' , 6 ' -p o s i t i on s wou l d s t e r i ca l l y p rev en t t h e p h eny l g rou p o ft h e b enzoy l g rou p f rom b e ing cop l ana r wi th t h e r e s t o f th e mo l ecu l e . Th e s i x ch a l cones s t u d i ed ,( s ee Tab le 1 4 .6) ex h ib i t v C=O in t h e r eg ion 1 6 7 0 -1 6 8 4 c m -1 , and ex h i b i t v C=C i n t h e r eg ion1 6 0 5 - 1 6 2 0 c m - 1 . T h e f r e q ue n c y s e p a ra t io n b e t w e e n v C = O a n d v C = C v a ri e s b e t w e e n 5 9 a n d7 3 c m -1 (1 6 ). T h ese d a t a i nd ica t e t h a t t h e s e ch a l cones ex i s t in p l ana r s -c is con f i g u ra t i on s .Noncop l ana r ch a l cones were no t av a i l ab l e fo r s t u d y .

Tab le 1 4 .7a li s ts s ome fu nd am en t a l v ib ra t i on s fo r t h e con j u g a t ed k e t ones s t u d ied . Th e se g rou pf req u enc i e s a i d i n i d en t i fy i ng t h es e comp ou nd s b y ad d i t i ona l sp ec t ra - s t ru c tu re i d en t i f i c a t i on .

I N T R A M O L E C U L A R H Y D R O G E N B O N D I N GTab le 1 4 .8 l is t s IR d a t a fo r 2 -h y d rox y -5 -X-ace t o p h en one i n CC14 so lu t i on (3 8 0 0 -1 3 3 3 cm -1 ) andC S 2 s o l u t io n ( 1 3 3 3 - 4 0 0 c m - 1 ) . T h e i n t r a m o l e c u l a r v O H . . . O = C a n d 7 O H . . . O = C v i b ra t io n s f o r2 - h y d r o x y - 5 - X - a c e t o p h e n o n e w e r e p r e s e n t e d i n C h a p t e r 7 .


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V a r i a bl e s i n D a t a I n t e r p r e t a t i o n 295T h e v C = O . . . H O f r e q u e n c i e s f o r 2 - h y d r o x y - 5 - X - a c e t o p h e n o n e s o c c u r i n t h e r a n g e 1 6 4 1 -

1 6 5 8 c m - 1 ( 17 ). T h e s e c o m p o u n d s e x h ib i t v C = O - . . H O a t lo w e r f r e q u e n c y b y 40 4 - 1 0 c m - 1c o m p a r e d to n o n h y d r o g e n b o n d e d a c e t o p h e n o n e s d u e to th e s t r e n g t h o f t h e C = O . . . H O b o n d .I n t h e s o li d p h a s e ( N u j o l m u l l ) t h e v C = O - . - H O m o d e o c c u r s 1 3 to 1 7 c m - 1 l o w e r i n f re q u e n c yth an i n CC1 4 so lu t i on .

T h e 2 - h y d r o x y - 5 - X - a c e t o p h e n o n e s e x h i b i t c h a r a c t e r i s t i c v i b r a t i o n s i n t h e r a n g e 9 5 4 -9 7 3 c m - 1 [ C - C ( = ) - C s t r e tc h in g ] , 1 2 8 3 - 1 3 8 0 c m - 1 [ p he n y l -0 s t r e t c h in g ] , a n d 1 3 5 9 -1 3 80 c m - 1 [ s y m m e t r i c C H 3 b e n d i n g ] .

C Y C L O A L K A N O N E SI n t h e v a p o r p h a s e c y c l o a l k a n o n e s e x h i b i t v C = O f r e q ue n c i e s i n t h e ra n g e 1 7 1 9 - 1 8 1 6 c m - 1 ( 2 ).T h e f r e q u e n c i e s d e c r e a s e as t h e n u m b e r o f c a r b o n a t o m s i n t h e c y c l o a l k a n o n e r i n g in c r e a s e f r o m4 to 8 and 10 (1816 , 1765 , 1732 , 1721 , 1720 , and 1719 c m - 1 , r e sp ec t iv e ly ) . T h e b eh av io r o f t h ev C - O f r e qu e n c y i s a t t ri b u t e d to c h an g e s i n th e C - C ( = ) - C b o n d a n gl e . D u r i n g a c y cl e o f C - - Os t r e t c h in g , m o r e o r le s s e n e r g y i s r e q u i r e d t o m o v e t h e c a r b o n y l c a r b o n a t o m a s t h e C - C ( = ) - Cb o n d a n g le b e c o m e s s m a l le r o r l ar ge r th a n t h e n o r m a l C - C ( - - ) - C b o n d a n g le f or a n o p e n c h a i nk e t o n e s u c h a s d i m e t h y l k e t o n e ( a c e t o n e ) . T h i s i s b e c a u s e d u r i n g a c y c le o f C = O s t r e t c h i n g , t h eC - C ( = ) - C a n g le m u s t in c re a s e , a n d a s t h e s iz e o f t h e c y c lo a l k a n o n e C - C ( = ) - C a n g led e c r e a s e s f r o m n o r m a l b o n d a n g l e s ( c y c l o h e x a n o n e f o r e x a m p l e ) , t h e m o r e d i f f i c u l t i t i s f o r an o r m a l C = O v i b r a t io n t o o c cu r. C o n v e r s e ly , i n c a se s w h e r e t h e b o n d a n g l e is la r ge r t h a n n o r m a l ,t h e ea s i e r i t i s f o r t h e v C= O v ib r a t i on t o occu r .

T a bl e 1 4 .9 l is t s IR v a p o r - p h a s e d a t a a n d a s s i g n m e n t s f o r c y c l o b u t a n o n e a n d c y c l o p e n t a n o n e .T h e v C = O f r e q u e n c ie s w e r e a l r e a d y d i s c u s s e d h e r e . I t s h o u l d b e n o t e d t h a t v a s y m . C H 2, v s y m .C H 2 , C H 2 t w i s t in g , t h e r i n g d e f o r m a t i o n , a n d t h e f i rs t o v e r t o n e o f v C = O a ls o d e c r e a s e i nf r e q u e n c y w h i l e t h e C H 2 b e n d i n g m o d e i n c r e a s e s i n f r e q u e n c y a s t h e r i n g s iz e i s i n c r e a s e d f r o mf ou r t o f i v e ca r b on a tom s .

T a bl e 1 4. 10 li s ts t h e C = O s t r e t c h i n g f r e q u e n c ie s f o r c y c l o p e n t a n o n e a n d c y c l o h e x a n o n e i nth e v ap o r , n ea t , and so lu t i on p h a ses ( 1 8 ) .

C y c l o p e n t a n o n e e x h i b i ts v C = O a t 1 7 65 ( v a p o r ) a n d 1 7 3 9 . 2 c m - 1 i n n e a t p h a s e a f t e rc o r r e c t io n f o r F e r m i r e s o n a n c e ( 1 8) . I n a ll s o l u t i o n s , v C - - O h a s b e e n c o r r e c t e d f o r F e r m ir e s o n an c e . C y c l o p e n t a n o n e e x h i bi t s v C = O a t 1 7 5 0 . 6 c m - 1 i n n - h e x a n e s o l u t io n a n d a t1 7 2 8 . 8 c m -1 i n w a t e r s o l ut io n . C y c l o h e x a n o n e e x h ib i ts v C = O a t 1 7 2 3 c m - 1 i n n - h e x a n eso lu t i on and a t 1 7 0 1 c m - 1 i n e t h y l a l c o h o l s o l u t i o n . A f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e ,v C - - O f o r c y c lo p e n t a n o n e d e c r e a s e s i n f re q u e n c y b y a p p r o x i m a t e l y 1 7 .1 c m - 1 p r o g r e s s i n g i n t h es e r ie s o f s o l v e n t s h e x a n e t h r o u g h m e t h y l a l c o h o l ( 1 8 ). P r o g r e s s i n g i n t h e s a m e s e r i e s o f s o l v e n t s ,v C = O f o r c y c l o h e x a n o n e d e c r e a s e s i n f r e q u e n c y b y a p p r o x i m a t e l y 2 2 c m - 1 . T h e C = O g r o u p f o rc y c l o h e x a n o n e i s m o r e b a s i c t h a n t h e C = O g r o u p f o r c y c l o p e n t a n o n e , a n d t h i s i s g i v e n a s t h er e a s o n t h a t t h e r e i s m o r e o f a s o l u t e - s o l v e n t i n t e r a c t i o n i n t h e c a s e o f c y c l o h e x a n o n e t h a n i n t h ec a se o f c y c l o p e n t a n o n e ( 1 8) . T h e v C = O f r e q u e n c ie s f o r t h e s e t w o c y c l o a l k a n o n e s d o n o tc o r r e la t e w e l l w i t h t h e s o l v e n t a c c e p t o r n u m b e r s ( A N ) , a n d t h i s is a t t r i b u t e d t o s t e r ic f a c to r s o ft h e s o l v e n t s t h a t h i n d e r s o l u t e - s o l v e n t i n t e r a c t i o n .

F i g u r e 1 4 .5 s h o w s a p lo t o f v C = O f o r c y c o h e x a n o n e v s m o l e % CHC13/n-C6H14.Def in i t eb r e a k s i n t h e p lo t a r e n o t e d a t ~ 2 . 5 t o 1 , ~ 6 t o 1 , ~ 5 0 t o 1 , a n d ~ 6 2 . 1 t o 1 m o l o f C H C 1 3 t oi m o l c y c l o h e x a n o n e . T h e c a u s e o f th e s e v C = O f r e q u e n c y s h i ft s i s m o s t l i k e l y a re s u l t o f


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296 Ketonesdifferent hydrogen bonding complexes between C - O and CHC13 which changes with increasingCHC13 concentration, that is,

(CH2)sC=O...HCCI3(C H2)sC= O ' ' " H C C 13(HCCI3)nCHCCI3(HCCIs)n

(CH2)sC=OCHCCI3(HCCI3)n

The general decrease in the vC=O frequency most likely is the result of continual change insolvent dielectric effect. Figure 14.6 shows a plot of vC=O for cyclohexanone vs mole %CC14/n-C6H14. This linear plot decreases in frequency as the mole % CC14/n-C6H14 increases.The dielectric effect of this solvent mixture increases as the mole % CC14/n-C6H14 increases,causing vC--O to occur at lower frequency in a linear manner. Unlike CHC13, there are nodifferent CC14 solute complexes as noted.

Figure 14.7 show a plot of vC= O for 0.345mo1% acetone in CHC13/CC14 solut ion vs themole % CHC13/CC14 (19). This plo t shows that it is linear over the mole % CHC13/CC14 rangeof ~1 7-100% . Extrapolation of the linear plot to zero mol% CHC13 indicates that the vC=Ofrequency for acetone in the range 0-17% ratio CHC13/CC14 varies from linearity by ~1 cm -1.The mole fraction of CHC13 is in excess of the 0.345mo1% acetone present, even at the1.49 mol % ratio CHC13/CC14 where the CHC13 protons forms weak hydrogen bonds between C1atoms of other CHC13 molecules and CCI4 molecules as well as with the carbonyl oxygen atom( 1 9 ) .

F i g u r e 1 4 . 8 s h o w s a p l o t o f t h e v C - O f r e q u e n c y f o r a c e t o n e v s t h e r e ac t i o n f i el d f o r e a c h o fthe mole % CHC13/CC14 solutions. Comparison of Fig. 14.7 with Fig. 14.8 shows that the

( e - 1) with e the dielectric constant of eachurves are identical. The reaction field JR] 2e + n 2'solvent, and n the refractive index of each solvent. A plot of mole % CHC13/CC14 vs the reactionfield yields a linear curve (19). Therefore, it appears as though the refractive index of the solventas well as the dielectric value of the solvent system together with intermolecular hydrogenbonding with C=O of the solute affects the induced frequency shift of vC=O in solution withCHC13/CC14. In summary, the frequency behavior of the solvent-induced ketone carbonylstretching vibration, vC=O, is affected by the reaction field, inductive effects, and solute-solventintermolecular hydrogen bonding (29).

Table 14.11 lists IR data for 14H-dibenzo[a, j]xanthen-14-one in CHC13/CC14 and in varioussolvents (20). This ketone has the following empirical structure:

"~ o / / "

I


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Variables in Data Interpretation 2 9 7F o r s i m p li ci t y, t h i s c o m p o u n d i s g i v e n t h e n a m e D X - 1 4 - O . T h e m a x i m u m s y m m e t r y fo rD X - 1 4 -O i s C 2v . T h e v C - - O m o d e b e l o n g s t o t h e A 1 sp ec i e s i f it h a s C2v sy m m et r y . T h e DX-1 4 -O h a s t w o s i g n i f ic a n t I R b a n d s i n t h e r e g i o n e x p e c t e d f o r v C - -O , a n d a s o l u t i o n s t u d y i nC H C 13 /C C 14 s o l u t i o n w a s u s e d t o h e l p e x p l a i n t h e p r e s e n c e o f th e s e t w o I R b a n d s . I n o r d e r f o rv C = O t o b e in F e r m i r e s o n a n c e i n t h e c as e o f D X - 1 4 -O b o t h t h e c o m b i n a t i o n ( C T ) o r o v e r t o n e( O T ) a n d v C - - O m u s t b e l o n g t o t h e A 1 s y m m e t r y sp e c ie s . In a d d i t io n , t h e C T o r O T w o u l d h a v et o o c c u r in t h e r a n g e e x p e c t e d f o r v C = O . I t i s o b v i o u s f r o m t h e k e t o n e s t r u c t u r e g i v e n h e r e t h a tt h e I R d o u b l e t c o u l d n o t b e d u e t o t h e p r e s e n c e o f r o t a t i o n a l i s o m e r s .

F ig u r e 1 4 .9 sh o ws I R sp ec t r a o f DX- 1 4 - O in t h e r eg ion 1 5 5 0 - 1 8 0 0 c m - 1 . Sp ec t r u m ( A) i s f o ra s a t u r a t e d s o l u t i o n i n h e x a n e , s p e c t r u m ( B ) i s f o r a s a t u r a t e d s o l u t i o n i n c a r b o n t e t r a c h l o r i d e ,a n d s p e c t r u m ( C ) i s f o r a 0 . 5 % s o l u t i o n i n c h l o r o f o r m . I n h e x a n e t h e I R b a n d s o c c u r a t 1 6 5 1. 9a n d 1 6 3 6 . 8 c m - 1 , i n c a r b o n t e t r a c h l o r id e t h e b a n d s o c c u r a t 1 6 4 8 .9 a n d 1 6 3 4 . 9 c m - 1 , a n d i nch lo r o f o r m th e b and s occu r a t 1 6 4 5 .4 and 1 6 3 3 .1 c m - 1 . I n s p e c t i o n o f t h e i r IR s p e c t ra s h o w s t h a tt h e a b s o r b a n c e r a t i o o f t h e l o w f r e q u e n c y b a n d t o t h e h i g h f r e q u e n c y b a n d i n c r e a s e s i n t h es o l v e n t o r d e r n - C 6 H 1 4 , C C 1 4 , CHC1 3 . F ig u r e 1 4 .10 sh ow s a p lo t o f v C- - O and th e OT o r CT inF e r m i re s o n a n c e , a n d v C = O a n d O T o r C T c o r r e c t e d f o r F e r m i r e s o n a n c e . T h e c o r r e c t e d d a tas h o w t h a t u n p e r t u r b e d v C - - O o c c u r s a t h i g h e r f r e q u e n c y t h a n u n p e r t u r b e d O T o r C T a t m o l e %C H C 13 /C C 14 b e l o w ~ 28 % ; a t m o l e % C H C 13 /C C 1 4 a b o v e ~ 2 8 % u n p e r t u r b e d v C = O o c c u r s ata l o w e r f r e q u e n c y t h a n u n p e r t u r b e d O T o r C T . W i t h o u t F R c o r r e c t i o n , e a c h I R b a n d r e s u l ts f r o ms o m e c o m b i n a t i o n o f v C = O a n d t h e O T o r C T. A t th e ~ 2 8 m o l % C H C 1 3/ CC 1 4, b o t h I R b a n d sr e s u l t f ro m e q u a l c o n t r i b u t i o n s o f v C = O o r O T o r C T .

F i g u r e 1 4 .1 1 s h o w s p l o t s o f v C - - O a n d O T o r C T a n d t h e i r c o r r e c t e d f r e q u e n c i e s v s t h es o l v e n t a c c e p t o r n u m b e r ( A N ) f o r e a c h o f t h e e i g h t s o l v e n t s , n u m b e r e d 1 - 8 , a n d l is t e ds e q u e n t i c a l l y . T h e s e p l o t s s h o w t h a t i n g e n e r a l t h e t w o m o d e s i n F e r m i r e s o n a n c e a n du n p e r t u r b e d v C = O d e c r e a s e i n fr e q u e n c y a s t he A N o f t h e s o l v e n t i s i n c r e a s e d . T h e s c a t t e r in go f d a t a p o in t s su g g e s t s t h a t t h e AN v a lu es d o n o t t ak e i n t o acco u n t t h e s t e r i c fac to r o f t h es o l v e n t , w h i c h c a u s e s v a r i a n c e i n t h e s o l u t e - s o l v e n t i n t e r a c t i o n . I t s h o u l d b e n o t e d t h a tu n p e r t u r b e d v C = O o c c u rs a t l o w e r f re q u e n c y t h a n t h e O C o r O T in o n l y c h lo r o f o r m a n db e n z o n i t r i l e s o l u t i o n s .

S U B S T I T U T E D 1 , 4 - B E N Z O Q U I N O N E ST h e k e t o n e 1 , 4 - b e n z o q u i n o n e h a s t h e f o l l o w i n g p l a n a r s t r u c t u r e :

I t h a s t w o C - - O g r o u p s , a n d t h e s e c o u p l e i n t o a n i n - p h a s e ( C - - O ) 2 s t r e t c h i n g v i b ra t i o n ,r ip ( C- - O) 2 , and a n ou t - o f - p h a se ( C- - O) 2 s t r e t ch in g v ib r a t ion , Vop (C= O) 2. I n CC1 4 so lu t i o n , 1 ,4 -b e n z o q u i n o n e e x h i b i t s a s t r o n g I R b a n d a t 1 6 7 0 c m - 1 a n d a m e d i u m s t r o n g b a n d a t 1 6 5 6 c m - 1 .W i t h o u t c o n s i d e r at i o n o f t he m o l e c u l ar s y m m e t r y o f 1 ,4 - b e n z o q ui n o n e , i t w o u l d s e e m r e a s o n -ab l e t o a s s ig n th e 1 6 7 0 c m - 1 b and t o Vop (C-- O) 2 and th e 1 6 5 6 c m - 1 b a nd t o Yip(C--O)2.H o w e v e r , 1 , 4 - b e n z o q u i n o n e h a s a c e n t e r o f s y m m e t r y a n d i t h as V h s y m m e t r y . T h e 3 0f u nd a m e n ta l s a r e d i s t r i b u t e d a s 6 A g , 1 Big 3 B2 g , 5 Blu , 52 u , and 3 B u. On ly th e u c l a s s e s a r e I R


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298 Ketonesac t iv e , and on ly t h e g c l a s s e s a r e Ram an ac t iv e . T h e Vop ( C= O) 2 m od e b e long s t o t h e b lu sp ec i e s ,a n d th e Vip( C=O) 2 m o d e b e lo ng t o t h e Ag sp ec i e s . Of cou r s e , 1 ,4 - b en zoq u in one can no t h av er o t a t i o n a l c o n f o r m e r s . T h e r e f o r e , o n e o f t h e f o r e m e n t i o n e d I R b a n d s e i t h e r re s u l t s f ro m t h ep r e s e n c e o f a n i m p u r it y , o r e ls e i t m u s t r e s u l t f ro m a B lu c o m b i n a t i o n t o n e i n F e r m i r e s o n a n c ew i t h the ~,op(C=O)2, b lu f u n d a m e n t a l . I t c o u l d n o t b e i n F e r m i r e s o n a n c e f r o m a n o v e r t o n e o f al owe r l y ing f u nd am e n ta l , b ecau se a f ir s t ov e r t one wo u ld b e lo ng t o t h e Ag sp ec i e s . T h e Ram anb an d a t 1 6 6 1 .4 cm - 1 i n CC1 4 so lu t i o n i s a s s ig ned t o t h e r i p ( C- - O) 2 , Ag m o d e .

F ig u r e 1 4 .1 2 sh ows p lo t s o f Vop (C= O ) , b lu and th e C T B lu m od e s i n F e r m i r e son ance , andt h e i r u n p e r t u r b e d f r e q u e n c i e s a f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e f o r 1 , 4 - b e n z o n o n e i n 0 . 5 %w t . / v o l , o r le s s i n 0 - 1 0 0 m o 1 % C H C 13 /C C 14 . T h e t w o o b s e r v e d I R b a n d f r e qu e n c i e s i n F e r m ir e sonance i n t h i s c a s e i nc r ea se i n f r eq u ency a s t h e m o le % CHC1 3 /CC1 4 i s i n c r ea sed . Howev er ,u n p e r t u r b e d Vop(C--O)2 decrease s i n f r eq u ency a s t h e m o le % CHC1 3/CC14 inc r ea ses , and th i s i sa lway s t h e ca se f o r o th e r c a r b ony l con t a in ing co m p ou nd s a s t h e m o le % CHC1 3/CC14 isi n c re a s e d . I t i s n o t e d t h a t t h e u n p e r t u r b e d C T b lu m o d e i n c r e a s e s i n f r e q u e n c y a s t h e m o l e %CHC1 3/CC14 is i n c r ea sed f r om 0 - 1 0 0 % . I n t hi s c as e , a t ~ ,2 5 m o l% CHC1 3/CC14 b o th I R b and sr e s u l t f r o m e q u a l c o n t r i b u t i o n s f r o m Vop(C--O)2 an d t h e C T blu m o d e .

T ab l e 1 4 .1 2 l is t s I R and R am an d a t a f o r s ev e r a l 1 ,4 - b en zoq u in one s i n C C I 4 and CHC1 3s o l u t i o n s ( at 0 . 5 % w t / v o l , o r l e ss d u e t o s a t u r a t io n ) . T h e p o i n t g r o u p p e r t a i n i n g t o t h e i rm o l e c u l a r s y m m e t r y i s g i v e n fo r e a c h o f t h e s e k e t o n e s . N o n e o f t h e o t h e r 1 , 4 - b e n z o q u i n o n e ss h o w I R e v i d e n c e f o r th e Vop ( C= O) 2 m od e b e ing i n Fe r m i r e sonance . The Vop(C=O)2 mode fort h e s e 1 , 4 -b e n z o q u i n e s o c c u r s i n t h e r a n g e 1 6 5 7 - 1 7 0 2 . 7 c m - 1 i n C C 1 4 s o l u t i o n a n d a t s l ig h t lylowe r f r eq u en cy i n CHC1 3 so lu t i on . I n CHC1 3 so lu t i on , V ip( C=O) 2 occu r s i n t h e r ang e 1 6 6 6 .9 -1 6 9 7 .7 cm - 1 . T h e i nc r ea s ing i n d u c t iv e e f fec t o f t h e h a log e n a tom s ( p r og r es s i n g i n t h e o r d e r Br ,C1 , F) together wi th thei r f ie ld ef fec t increase bo th Vop(C=O)2 and Vip(C=O)2 f r eq u enc i e s ( 2 2 ) .

T a bl e s 1 4 . 1 3 - 1 4 . 1 7 l i st IR da t a f or t e t r a f l u o r o - l , 4 -b e n z o q u i n o n e , t e t r a c h l o r o - l , 4 - b e n z o q u i -n o n e , t e t r a b r o m o - 1 , 4 - be n z o q u i n o n e , c h l o ro - 1 , 4 - b e n z o q u i n o n e , a n d 2 , 5 - d i c h l o r o b e n z o - q u i n o n ein t h r ee d i f f e r en t s o lv en t sy s t em s .

I n t h e I R, t e t r a f l u o r o - l ,4 - b e n z o q u i n o n e e x h i b it s s t r o n g I R b a n d s a t 1 7 0 2 .7 a n d 1 6 6 7 . 6 c m - 1in CC 1 4 so lu t i on and a t 1 7 0 1 .4 and 1 6 6 8 .4 cm - 1 i n CHC1 3 so lu t i on . I n a l l c a s e s t h e h ig h e rf r e q u e n c y b a n d h a s m o r e i n t e n s i t y t h a n t h e l o w e r f r e q u e n c y b a n d . T h e s e t w o I R a r e a s s i g n e d t oVop(C=O)2 and Vop(C=C ) , r espec t ively . Figu re 14 .13 sho ws p lo ts of Vop(C--O)2 and Vop(C=C)2f o r 1 ,4 - t e t r a f lu o r o b en zoq u in on e v s m o le% CHC1 3 /CC1 4 . T h e Vop (C= O)2 m o d e d ec r ea ses i nf r eq u ency a s ex p ec t ed a s t h e m o le% CHC1 3 /CC1 4 i s i n c r ea sed . T h e Vop ( C= C) 2 r i ng m od einc r ea ses i n f r eq u en cy a s t h e m o le% CHC1 3/CC14 is i n c r ea sed .

T h e f r e q u e n c y b e h a v i o r o f t h e o t h e r s u b s t i t u t e d 1 , 4 - b e n z o p h e n o n e s i s d i s c u s s e d i n d e ta i l i nRef e r ence 2 1 , and th e r ead e r i s r e f e r r ed t o t h i s p ap e r f o r f u r th e r i n f o r m a t i on on th es e i n t e r e s t i ngs o l u t e - s o l v e n t i n t e r ac t i o n s .

T ab l e 1 4 .18 l is t s I R d a t a f o r 3 , 3 ' , 5 , 5 ' - t e t r a a lk y l - l , 4 - d ip h e no q u ino ne s i n CHC1 3 so lu t i o n andi n t h e s o l i d p h a s e ( 2 2 ) . T h e 3 , 3 ' , 5 , 5 ' - t e t r a a l k y l - l , 4 - d i p h e n o q u i n o n e s h a v e t h e f o l l o w i n gem p i r i ca l s t r u c tu r e :

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13/44

Var iables in Data In terpre ta t ion 2 9 9W h e n t h e 3 , 3 ' , 5 , 5 ' p o s i t i o n s a r e s u b s t i t u t e d w i t h i d e n t i c a l a t o m s o r g r o u p s , t h e c o m p o u n d sh a v e D 2h s y m m e t r y ( 2 2 ) . T h e s e m o l e c u l e s h a v e a c e n t e r o f s y m m e t r y , a n d o n l y t h e V o p ( C - O ) ,B3u fun dam en tal i s IR act ive . Th e Vop(C----O)2, Ag fun da me nt al i s on ly R am an act ive . Th eV o p( C- -O )2 m o d e f o r t he 3 , 3 ' , 5 , 5 ' - t e t r a a l k y l - l , 4 - d i p h e n o q u i n o n e s o c c u r s i n t h e r a n g e 1 5 8 6 -1 6 0 2 c m - 1 i n t h e s o l i d p h a s e a n d i n t h e r a n g e 1 5 8 8 - 1 5 9 9 c m - 1 i n C H C 1 3 s o l u t i o n . T h ec o m p o u n d 3 , 3 ' - d i m e t h y l , 5 , 5 ' - d i - t e r t - b u t y l - l , 4 - d i p h e n o q u i n o n e h a s C z v s y m m e t r y , a n d i n t h i scase bo th V ip(C=O)2 a re IR act ive a s we l l a s Ram an ac t ive . I n th i s case the IR ban d a t 1603 c m - 1i s a s s igned to bo th Vop(C-O)2 and r ip (C-O)2 . The f r equenc ie s in b racke t s i n Tab le 14 . 18 a r eca lcu la t ed . A l l o f the se f ive 3 , 3 ' , 5 , 5 ' - t e t r aa lky l - l , 4 -d iph en oqu ino ne s exh ib i t a wea k IR band int h e r a n g e 3 1 6 8 - 3 2 0 4 c m - 1 i n t h e s o l i d p h a s e a n d i n t h e r a n g e 3 1 7 5 - 3 2 0 0 c m - 1 i n C H C1 3so lu t ion . The se bands a r e a s s igned to the combina t ion tone Vop(C- -O)2 + r ip (C- -O)2 . Us ing theo b s e r v e d V o p (C - -O ) 2 a n d c o m b i n a t i o n t o n e f r e q u e n c i e s f o r t h e s e c o m p o u n d s , t h e r i p ( C - O ) 2f r equenc ie s a r e ca lcu la t ed to occu r in the r ange 1579-1601 c m - 1 i n t h e s o l i d p h a s e a n d i n t h er a n g e 1 5 8 3 - 1 6 0 2 c m - 1 C H C 1 3 s o l u t i o n ( 2 2) . T h e s e d a t a c o n f i r m a p r e v i o u s c o n c l u s i o n t h a td i p h e n o q u i n o n e s e x h i b it a s t r o n g I R b a n d n e a r 1 6 0 0 c m - 1 , w h i c h m u s t i n c l u d e s t r e t c h i n g o f t h eC - - O b o n d ( 2 3 ) . T h u s , i t i s p o s s i b l e t o d i s t i n g u i s h b e t w e e n 4 , 4 ' - d i p h e n o q u i n o n e s a n d 1 , 4 -b e n z o q u i n o n e s , s i n c e t h e l a t t e r c o m p o u n d s e x h i b i t c a r b o n y l s t r e t c h i n g m o d e s 3 0 t o 8 0 c m - 1h ighe r in f r equency (21 ) .

C O N C E N T R A T I O N E F F E C T ST a bl e 1 4 .1 9 li s ts d a t a t h a t s h o w t h e d e p e n d e n c e o f t h e v C = O f r e q u e n c y o f d i a lk y l k e t o n e s u p o nt h e w t . /v o l . % k e t o n e i n s o l u t i o n w i t h C C 1 4 o r CHC13 (10) . In C C 1 4 s o l u t i o n , t h e v C = O m o d ef o r d i i s o p r o p y l k e t o n e d e c re a s e s m o r e i n f re q u e n c y i n g o i n g f ro m ~ 0 . 8 % t o 5 . 2 5 % t h a n i t d o e sf o r d i - t e rt - b u t y l k e t o n e a t c o m p a r a b l e w t . / v o l , k e t o n e i n C C 1 4 s o l u t i o n ( - 0 . 1 9 t o - - 0 . 0 8 c m - 1 a t5 . 2 5 % w t . / v o l . ) . I n C H C 13 s o l u t i o n , t h e s h i ft o f v C - O i s i n t h e o p p o s i t e d i r e c t i o n t o t h a t n o t e dfo r C C 1 4 s o l u t i o n s . A t 5 . 8 9 % w t . / v o l , i n C H C 1 3 s o l u t i o n , v C = O i n c r e as e 0 . 3 8 c m - 1 fo rd i i s o p r o p y l k e t o n e a n d a t 5 . 7 8 w t . / v o l . i n C H C 1 3 f o r d i - t e r t -b u t y l k e t o n e t h e i n c r e a s e is0.1 r - 1 . T h e s m a l l e r v C - O f r e q u e n c y s h i f t s i n t h e c a s e o f t h e d i - t e r t - b u t y l a n a l o g c o m p a r e dto the d i i so p ropy l an a log i s a t t r ibu te d to s t e r ic f ac to r s o f the a lky l g roup . T he s t e r i c f ac to r o f thet e r t - b u t y l g r o u p s d o e s n o t a l l o w a s m u c h s o l u t e - s o l v e n t i n t e r a c t i o n b e t w e e n C - O a n d t h eso lven t a s i t doe s in the case o f the d i i sop ropy l ana log . Wi th inc r ease in the w t . /vo l , o fke ton e /CHC 13 v C= O in c r ease s in f r equency , i nd ica t ing th a t the s t r eng th o f the C- - -O .. .HCC12C 1 - - . ( H C C l z C 1 ) n i n t e r m o l e c u l a r h y d r o g e n b o n d b e c o m e s w e a k e r a s n b e c o m e s s m a l l e r .

R E F E R E N C E S1. Schrader, B. (1989). Raman/Infrared Atlas of Organic Compounds, 2nd ed., Weinheim , German y: VCH.2. Nyquis t, R. A. (1984). The Interpretat ion of Vapor-Phase Infrared Spectra: Grou p Frequency D ata, Philadelphia: SadtlerResearch Laboratories, a Division of Bio-Rad Labortories, Inc.3. Hallam , H. E. (1963). Infra-Red Spectroscopy and Molecular Structure, p. 420 , M. Davies, ed., New York: Elsevier.4. Kirkwood,J. G ., West, W., and Edwards , R. T. (1937).J . Ch em. Phys . , 5, 14.5. Baue r E. and M agot, M. (1938).J. Phys. Radium, 9, 319.


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3 0 0 K e t o n e s6. Jos ien M. L . and Fuson , N . (1954) . J. C hem . Phys. , 22, 1264.7. Bellamy, L. J. , Hallam , H. E., and William s, R. L. (1959). Trans. Farad. So c. , 55, 1677.8. Nyquist, R. A. (1989). Appl. Spectrosc., 43, 1208.9. Nyquist, R. A. (1994). Vib. Spectrosc., 7, 1.

10. Nyq uist, R. A. , Putzig, C .L. , and Yurga, L. (1989). Appl. Spectrosc., 43, 983.11. Nyquist, R. A. (1986). Appl. Spectrosc., 40, 79.12. Nyq uist, R. A. , Chrz an, V., and Ho uck, J. (1989). Appl. Spectrosc., 43, 981.13. Lin-Vien, D. , Coh hup , N. B. , Fatelely, W. G. , and Grasse lli , J. G. (199 1). The Handbook of Infrared and RamanCharacteristic Group F requencies of Organic Molecules, San Diego: Academic P ress , Inc .14. B owles, A. J. , George, W. O. , and Ma ddam s, W E (1969) J. Chem. Soc., B, 810.15. Cotte e, E H., Straug ham, B. P., Tim mo ns, C. J. , Forbes, W E, and Shilto n, R. (1967). J. Chem. Soc. , B, 1146.16. (1982) Sadtler Standard Infrared Vapor phase Spectra, Phi lade lphia: Sadt le r Research Laborator ies , a Divis ion o f B io-

Rad, Inc.17. Nyquist, R. A. (1963). Spectrochim. Acta, 19, 1655.18. Nyquist, R. A. (1990). Appl. Spectrosc., 44, 426.19. Nyquist, R. A. , Putzig, C. L. , and Hasha, D. L. (1989). Appl. Spectrosc., 43, 1049.20. Nyq uist, R. A. , Luo ma, D. A. , and W ilken ing, D. , (1991). Vib. Spectrosc., 2, 61.21. Nyq uist, R. A. , Luo ma, D. A., and Putzig, C. L. (1992). Vib. Spectrosc., 3, 181.22. Nyquist, R. A. (1982). Appl. Spectrosc., 36, 533.23. Gord on J. M. and Fo rbes , J . W (1968) . Appl. Spectrosc., 15, 19.


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