Aldehydes in physics

7/28/2019 Aldehydes in physics

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C H A P T E R 1 3AldehydesReferences 270Figures TablesFigure 13-1 271 (268)Figure 13-2 272 (268)Figure 13-3 273 (268)Figure 13-4 274 (269)Figure 13-5 275 (269)Figure 13-6 276 (269)Figure 13-7 277 (270)Figure 13-8 278 (270)Figure 13-9 279 (270)Figure 13-10 280 (270)Figure 13-11 281 (270)

Table 13-1Table 13-1aTable 13-2Table 13-3Table 13-4Table 13-5Table 13-6

282 (267)282 (268)282 (268)283 (269)284 (269)285 (270)286 (270)

*Numbers in parentheses indicate in-text page reference.A ldehydes a r e eas i ly ox id ized to the co r r es pond ing ca rboxy l ic ac id . There fo re , the r eader i scau t ioned to look for the p res ence o f ca rboxy l ic ac id impu r i t i e s wh en in te rp re t ing the IR o rRam an s pec t r a o f a ldehydes . S evera l pub l i s h ed s pec t r a o f a ldehydes con ta in ac id impur i ty , andt h e i m p u r i t y i s n o t m a r k e d o n t h e I R s p e c t r u m .

A l d e h y d e s c o n ta i n t h e O = C - H g r o u p ; t he e m p i r ic a l s t r u c tu r e f o r t h e a li p h a ti c f o r m s isR - C ( = O ) H , f o r t h e c o n j u g a t e d f o r m i t i s C = C - C ( - - O ) H , a n d f o r t h e a r o m a t i c f o r m i t i sC6 Hs C (=O )H. Charac te r i s t i c v ib ra t ions o f the a ldehyde g roup a re :

a) C-- -O s t re tch ing ( IR, s t rong ) ;b ) the f i rs t over tone o f C- -O s t r e tch ing ( IR ve ry weak) ;c ) C - H b e n d i n g ( IR , m e d i u m ) ; a n dd ) C - - H s t r e tc h i n g in F e rm i r e so n a n c e w i t h C - H b e n d i n g ( IR , w e a k - m e d i u m b a n d s ) .Tab le 13 . 1 compares IR da ta and as s ignmen ts fo r s ome noncon juga ted a ldehydes r eco rded in

d i f f e r en t phys ica l phas es . In a l l cas es the vC- -O f r equency occur s a t h igher f r equency in the


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268 Aldehydesin the o rde r o f Br, C1, and F s ubs t i tu t ion . The ind uc t ive pow er o f the ha logen a tom a l so inc reas esin th is same order .

T h e a ld e h y d i c i n - p la n e ( O = C - H p l a n e ) b e n d i n g m o d e o c c u r s i n t h e r e g i o n 1 3 5 0 -1400 cm -1 , and i t s f ir s t over ton e (2c5CH) in F erm i r es onanc e w i th v C - H occur s in the r eg ions2 8 0 0 - 2 8 6 0 c m - 1 a n d 2 6 8 0 - 2 7 2 2 c m - 1 . U s u a ll y t h e h i g h e r f 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 it ythan the lower f r equency band in the F ermi r es onance doub le t . However , s omet imes the twobands have nea r ly equa l o r equa l in tens i ty . Where bo th bands o f the F ermi doub le t have equa li n te n si ty , b o t h b a n d s r e s ul t f ro m e q u a l m i x t u r e s o f v C - H a n d 2 6 C - H . I t i s n o t t h e o r e t ic a l lyc o r r e c t to a s si g n t he s t r o n g e r o f t h e t w o b a n d s t o o n l y th e v C - H f u n d a m e n t a l .

Tr ich lo roace ta ldehyde does fo rm a hydra te , and in i t s hydra te fo rm i t i s no longer ana ldehyde . I t ex i st s a s a d ihydrox ide , CC13CH(OH) 2.

Tab le 13 . 1a l i s t Raman da ta and as s ignmen ts fo r s evera l a ldehydes . The Raman da ta weretaken f rom Refe rence (4 ) , and the as s ignmen ts were made by Nyqu is t . Da ta in the pa ren thes esind ica te the r e la tive Rama n band in tens i t i e s and p i s po la r i zed . Thes e da ta s h ow tha t the r e la t iveRam an band in tens i ty fo r vC =O i s l e ss than tha t fo r the band in tens i t i e s fo r v C -H and 2c5CH inF ermi r es onance .

A c ro l ei n is a co n j u ga t e d a ld e h yd e , C H 2 = C H - C ( = O ) H a n d t h e R a m a n b a n d s a t 1 6 8 8 c m - 1and 161 8cm -1 a r e as s igned to vC= O and v C= C, r espec tive ly . Benza ldehyde , C 6H s C( - -O )H , i sa l so con juga ted , and i t s vC= O mo de oc cur s a t 1701 cm -1 in the cond ens ed phas e . In the case o fs a li c y la l d e hy d e , o r 2 - h y d r o x y b e n z a l d e h y d e , t h e O H g r o u p i s i n t r a m o l e c u l a r ly h y d r o g e n b o n d e dt o t he C = O g r o u p , a n d i ts v C = O m o d e o c c u r s a t 1 6 33 c m - 1 i n t h e c o n d e n s e d p h a s e .

Table 13.2 lis ts IR data for 4-X-be nzald ehyd es in the vap or , CC14, and CHC13 solu t ion p hase s( 5 ). M a n y o f t h e v C = O f r eq u e n c ie s h a v e b e e n c o r re c t e d f o r F e r m i r e s o n a n c e ( v C = O i n F e r m ires onance w i th 2~C-H) . As s hown in F ig . 13 . 1 , the vC=O f r equenc ies genera l ly dec reas e as theHa mm et t o'p va lues dec reas e . Th i s f igu re s hows p lo t s o f vC =O fo r 4 -X-benz a ldehydes vsHam met t ' s typ va lue fo r the 4 -X a tom o r g roup . T he po in t s on each l ine co r r e s pond to vC =Ofrequenc ies a s s igned fo r the 0 -1 00 m ol % CHC13/CC14 s o lu t ions (5 ). F igu re 13 .2 s hows p lo t s o fvC =O fo r 4 -X-benza ldehyd es co r r ec ted fo r F e rmi r es onance in CC14 s o lu t ion vs the f r equencyd i ff e re n c e b e t w e e n v C = O c o r r e c te d f o r F e r m i r e s o n a n c e i n C C 1 4 s o l u t i o n m i n u s v C - - Ocorrected for FR for each of the mole % CHC13/CC14 solut ions for each of the 4-X-benzalde-hydes (5 ) . Thes e p lo t s aga in demons t r a te the e f f ec t o f the 4 -X s ubs t i tuen t upon vC=O as we l las the e f f ec t o f the s o lven t s ys tem. The mathemat ica l t r ea tmen t o f the exper imen ta l da tap res en ted he re a lways y ie lds a l inea r r e la t ions h ip .

F i g u r e 1 3 .3 s h o w s p l o t s o f v C = O a n d a n o v e r t o n e i n F e r m i r e s o n a n c e a n d t h e i r c o r r e c te df r equenc ies vs mole % CHC13/CC14 fo r 4 - ( t r i f luo romethy l ) benza ldehyde . Af te r co r r ec t ion fo rF R, i t can be r ead i ly s een tha t the co r r ec ted vC=O and OT f r equenc ies a r e c los e r in f r equencythan the i r uncor re c ted obs e rved f r equenc ies . F igu re 13 . 4 s how s p lo t s o f vC =O and O T in F ermires onance and the i r co r r ec ted f r equenc ies vs mole % CHC13/CC14 fo r 4 -b romobenza ldehyde . Inth i s case i t is no ted tha t the co r r ec ted vC =O and OT f r equenc ies conv erge a t - -~45 mol %


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Variables in Data Interpretation 2 6 9th e b u lk d i e l ect r ic e f fec t o f th e so lv en t sy s t em to g e t h e r w i th i n t e rmo lecu l a r h y d ro g en b o n d in g o ff o r m C = O - - . H C C 1 3 .

Table 13 .3 l i st s the unpe rtur bed vC-- O frequencies of 4 -X-b enzaldehyd es in var ious so lventsy s t ems (6 ) . Th e 4 -X-b en za ld eh y d es d e s ig n a t ed wi th an a s t e r i sk (* ) l i s t t h e v C=O f req u en cyco r rec t ed fo r Fe rmi re so n an ce . Th e o v e ra l l v C=O f req u en cy ran g e fo r 4 -X-b en za l d eh y d es i s1 6 6 4 .4 -1 7 1 8 .1 cm -1 . T h e h ig h es t v C =O f req u en cy i s ex h ib i t ed b y 4 -n i t ro b en za ld eh y d e i nh ex an e an d t h e l o wes t v C=O f req u en cy i s ex h ib i t ed b y 4 - (d i me th y l amin o ) b en za ld eh y d e i nso l u t i o n i n m e t h y l a l co h o l.

F ig u re 1 3 .4 sh o ws p l o t s o f t h e v C=O f req u en cy fo r each o f t h e 4 -X-b en za l d eh y d es i n aso lv en t v s t h e v C= O f req u en cy d i ffe ren ce b e tween t h e v C =O f req u en cy in h ex an e so lu t i o n an deach of the o ther so lvents . These p lo ts a re s imi lar to the p lo ts shown in Fig . 13 .2 .

F ig u re 1 3 .5 sh o ws a p l o t o f v C=O fo r each o f t h e 4 -X-b en za ld eh y d es i n d ime th y l su l fo x id eso lu t ion vs Ham met t ' s crp va lues. O ther p lo ts o f vC =O for each of the 4-X-b enzaldehy des in eacho f t h e o t h e r so lv en t s sh o w s i mi l a r p l o t s wi th 4 -OH, 4 -CH3 -O, an d 4 -CH3 S an a lo g s n o tcorre la t ing as wel l as the o ther 4 -X analogs .

F ig u re 1 3 .6 sh o ws a p lo t o f v C- -O fo r 4 - (d i me th y l amin o b en za l d eh y d e v s t h e so lv en tacceptor number (AN) for each of the so lvents . So lvents a re l i s ted sequent ia l ly 1 th rough 17star t ing wi th hexane as 1 and 17 for methyl a lcohol . Two essen t ia l ly l inear re la t ionsh ips a renoted in th i s f igure . The p lo t 12 , 15 , 16 , and 17 represen ts vC=O.- .HOR frequencies for te r t -bu ty l a lcohol , i sopropyl a lcohol , e thy l a lcohol , and methyl a lcohol , respec t ive ly . The 4-( d i m e t h y l a m i n o ) b e n z a l d e h y d e w o u l d b e e x p e c t e d t o f o r m t h e s t r o n g e s t C = O . . - H O R b o n d ,because the (CH3)N grou p i s the m ost bas ic and the weak est i s the case of the 4-N O 2 analog .The lower l inear re la t ionsh ip i s fo r vC=O frequencies . Other 4-X-benzaldehydes in these sameso lv en t s sh o w s imi la r p lo ts wi th so me wh a t mo re sca t t e red d a t a p o in t s ( see (6 ) fo r o th e r p lo t s) .Th i s led t o t h e co n c l u s io n t h a t t h e so lu t e / so lv en t i n t e rac ti o n s a re co m p l ex b ecau se t h e so lv en ta l so in terac ts wi th cer ta in 4-X groups as wel l as w i th the zc system of the ph eny l g roup . The A Nvalues g ive a rough pred ic t ion of vC--O and vasym NO2, bu t do no t take in to account a l l o f theso lu te / so lvent in terac t ions (e .g . , s te r ic fac tors , re la t ive basic s i tes in the so lu te , in te rmolecularh y d ro g en b o n d in g b e tween so lv en t mo l ecu l e s v s b e tween so lu t e an d so lv en t mo lecu l e s ) .

In genera l , the Ha mm et t ~rp va lues for the 4-X a tom or group for 4 -X-b enzaldehy des ap pear tocorre la te wi th the v C= O frequencies . How ever , due to sca t te r ing of the da ta po in ts in the p lo ts ineach of the o ther so lvent sys tems (6) , these va lues do no t appear to take in to accounti n t e rmo lecu l a r h y d ro g en b o n d i n g , t h e re l a t i v e b a s i c i t y o f t h e C- -O g ro u p , an d t h e i n t e rac t i o nof the so lvent wi th o ther s i tes in the 4-X-benzaldehydes .Th e m o l ecu l a r g eo me t ry o f b o t h so lv en t an d so lu t e mo lecu l e s , t h e b a s ic an d / o r ac id i c s it e s inb o t h so lu t e an d so lv en t mo l ecu l e s , t h e d i p o l a r i n t e rac t i o n s b e t ween so lu t e an d so lv en tmolecules , the s te r ic fac tor o f so lu te molecules , and the concent ra t ion of the so lu te mostl ike ly de termine the overa l l so lu te / so lvent in terac t ion . Therefore , parameters such as AN valuesand H am m et t ~rp va lues can no t be expe cted to exhib i t un iversa l l inear re la t ionsh ips be tw een IR


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2 7 0 Aldehydesk n o w n t h a t t h e a l d e h y d i c C H s t r e t c h i n g m o d e , v C H , a n d t h e f i rs t o v e r t o n e o f t h e a l d e h y d i c C Hi n - p l a n e b e n d i n g m o d e , 2 ~ C H , a r e i n F e r m i r e s o n a n c e ( 8 - 1 2 ) . B e c a u s e ~ C H f r e q u e n c i e s a r ed e p e n d e n t u p o n t h e so l v e n t s y s t e m , o n e m i g h t e x p e c t t h a t th e a m o u n t o f F e r m i r e s o n a n c ei n t e r a c t i o n b e t w e e n v C - H a n d 2 ~ C H w o u l d a l s o b e d e p e n d e n t u p o n t h e s o l v e n t s y s t e m . T a b l e1 3 .5 l i s t s t h e c ~CH , c a l c u l a t e d 2 c ~CH , a n d 2 c ~CH f r e q u e n c i e s c o r r e c t e d f o r Fe r m i r e s o n a n c e i nb o t h C C | 4 a n d C H C 1 3 s o l u t i o n s . T h e a g r e e m e n t b e t w e e n t h e c a l c u l a t e d a n d c o r r e c t e d 2 ~ C Hf r e q u e n c i e s v a r ie s b e t w e e n ~ 0 . 4 t o 1 5 c m - 1 .

T a b le 1 3 . 6 li st s I R d a t a a n d a s s i g n m e n t s f o r t h e p e r t u r b e d a n d u n p e r t u r b e d v C - H f r e q u e n c i e sf o r t h e 4 - X - b e n z a l d e h y d e s ( 7 ) . T h e u n p e r t u r b e d v C - H f r e q u e n c i e s f o r 4 - X - b e n z a l d e h y d e s i nC C 1 4 s o l u t i o n o c c u r i n t h e r a n g e 2 7 6 8 . 7 - 2 7 8 9 . 7 c m - 1 a n d i n CH C1 3 s o l u t i o n i n t h e r a n g e2 7 7 6 . 6 - 2 8 0 8 . 9 c m - 1 .

F i g u r e 1 3 .7 s h o w s p l o t s o f h a l f o f th e F e r m i d o u b l e t f o r e a c h o f th e 4 - X - b e n z a l d e h y d e s i n t h er a n g e 2 7 2 6 - 2 7 4 6 c m - 1 v s mo l e % CH C1 3 /CC1 4 a n d F i g u r e 1 3 . 8 s h o w p l o t s o f h a l f o f t h e Fe r mid o u b l e t i n t h e r a n g e 2 8 0 5 - 2 8 4 5 c m - 1 v s m o l e % C H C 1 3 /C C 1 4. F i g u r e 1 3 .9 s h o w s p l o t s o fu n p e r t u r b e d v C H f o r e a c h o f t h e 4 - X - b e n z a l d e h y d e s v s mo l e % CH C1 3 / CC1 4 . T h e s e p l o t s s h o wt h a t t h e F e r m i d o u b l e t a n d t h e u n p e r t u r b e d v C H f r e q u e n c i e s i n c r e a s e i n f r e q u e n c y a s t h emo l e % CH C3 / CC1 4 i s i n c r e a s e d . H o w e v e r , t h e v C - H o r 2 c~ C H f r e q u e n c i e s a p p a r e n t l y d on o t c o r r e l a t e w i t h H a m m e t t ~rp v a l u e s b e c a u s e t h e p l o t s s h o w t h a t t h e f r e q u e n c i e s d o n o ti n c r e a s e o r d e c r e a s e i n t h e o r d e r 1 t h r o u g h 1 3 .

S u b m a x i m a a r e a l so n o t e d f o r 4 - X - b e n z a l d e h y d e s i n th e r a n g e 2 7 2 6 - 2 8 1 6 c m - 1 , a n d t h e s eb a n d s a r e a s s i g n e d t o c o m b i n a t i o n t o n e s .

B e n z a l d eh y d e a n d 4 - p h e n y l b e n z a l d e h y d e a r e e x a m p l e s o f h o w t h e u n p e r t u r b e d v C H a n du n p e r t u r b e d 2 ~ C H c r o s s ov e r w i t h c h a n g e i n t h e m o l e % C H C 1 3 /C C 1 4. I n t h e c a s e o fb e n z a l d e h y d e t h e c r o s s o v e r i s a t ~ 5 5 m o l % C H C 1 3/ C C1 4 a n d f o r 4 - p h e n y l b e n z a l d e h y d e t h ec r o s s o v e r i s a t ~3 5 mo l % CH C1 3/ CC1 4 ( s e e F i g u r e s 1 3 . 1 0 a n d 1 3 . 1 1 ).

R E F E R E N C E S1. Bellamy, L. J. a nd W illiams, R. L. (1958 ). J. Chem . Soc. London, 3645.2. Nyq uist, R. A. (1984). The Interpretation of Vapor-Phase Infrared Spectra: Group Frequency Data, Philadelphia: SadtlerResearch Labo ratories, Div. of Bio-Rad Inc.3. Lin-V ien, D., Co hhu p, N. B., Fately, W. G., and G rasselli, J. G . (1 991 ). The Handbook of Infrared and R aman Char-acteristic Frequencies or Organic Molecules, Boston: Academ ic Press, Inc.4. Schrader, B. (1989). Raman/Infrared Atlas of Organic Compounds, 2nd ed., Weinheim, Germany: VCH.5. Ny quis t, R. A., Settineri, S. E., and Lu om a, D. A. (1991 ). Appl. Spectrosc., 45, 1641.6. Nyq uist, R. A. (1992). Appl. Spectrosc., 46, 306.7. Nyq uist, R. A. (1992). Appl. Spectrosc., 46, 293.8. Pozefsky, A. and Cog geshall, N. D. (19 51) . Anal . Chem., 23, 1611.


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Aldehydes in physics