A SCF MO Treatment of Some Tropone Derivatives*

C R O A T I C A C H E M I C A A C T A 42 (1 97 0) 1

<CCA-565 539.19:547.5Original Scien tific Paper

A SCF MO Treatment of Some Tropone Derivatives*

M. J. S. D ew ar and N. Trinajstić**

D epartm ent of C hem istry, The U niversity o f Texas, A ustin , Texas 78712, U.S.A.

R e c e iv e d A u g u s t 9, 1969

Recent w ork in these laboratories has led to the developm ent of a sem iem pirical SCF MO trea tm en t w hich seems to give extrem ely good resu lts fo r ground States of conjugated molecules of ali kinds composed of carbon, hydrogen, n itrogen and oxygen.We have now applied th is trea tm en t to a problem of cu rren t in terest, nam ely the structu res of tropolone and tropone derivatives. The calculations lead to th e conclusion th a t n e ither of these ring system s is in itself arom atic, w hile tropone is now re - cognized to be polyenoid, tropolone still seems to be generally regarded as arom atic. This belief, how ever, arose from the behavior of tropolone derivatives in strong acid solution, w here they exist as hydroxy tropylium derivatives, o r in alkali w here they form m esom eric anions. C alculated heats of form ation, resonance energies, and bond lengths are reported.

IN T R O D U C T IO N

Some tim e ago one of u s1 concluded on th e basis of availab le Chemical <evidence th a t s tip ita tic acid and colchicine m u st contain a novel arom atic system , tropolone (I), contain ing a seven-m em bered ring . Subsequen t w ork not only confirm ed th is conclusion b u t also led to th e syn thesis of tropo lone2 itself, and of th e re la ted tropone3 (II); bo th these com pounds seem ed to show s tab ility characteristics of typ ica l arom atic system s, an d i t w as qu ick ly realized th a t th is m igh t be due to th e fac t th a t b o th I and II can be reg a rd ed as d e rivatives of th e tropy lium ion, C7H 7+, w hich H iickel4 in 1931 h ad p red ic ted to b e arom atic, a p red iction w hich has been fu lly confirm ed.5 H ow ever a lthough an enorm ous am ount of exp erim en ta l w ork has been ca rried ou t since th en on th e synthesis and p roperties of num erous tropone and tropolone derivatives, v e ry few th eo re tica l stud ies seem as y e t to have been reported . The only published investigations of g round State p ro p erties have been based on th e HMO m ethod,6’7 and a little w ork has also been rep o rted on exciteđ States.8

W hile th e HMO m ethod is know n to be q u ite u n re liab le fo r com pounds con ta in ing heteroatom s, m ore sa tisfac to ry procedures, based on th e Pople SCF MO trea tm en t, have been described in recen t years. The best of them , in so fa r as g round States a re concerned, is a sem iem pirical SCF MO tre a tm e n t th a t has been developed in these laboratories*1-12. In its c u rre n t form , th is

* This w ork w as supported by the A ir Force Office of Scientific Research th rough G ran t num ber AF-AFOSR-1050-67.

** Robert A. W elch Postdoctoral Fellow; on leave of absence from the »Ruđer Bošković« Institu te , Zagreb, Croatia, Yugoslavia.

2 M. J. S. DEWAR AND N. TRINAJSTIĆ

enables th e h ea ts of fo rm ation of a v e ry w ide v a rie ty of con jugated m o le- cules, bo th arom atic and non-arom atic , and contain ing n itrogen and /o r oxygen as w ell as carbon and hydrogen , to be calcu lated w ith in th e lim its of experim en ta l e rro rs in th e availab le therm ochem ical data. We th ere fo re though t it w ould be of in te re s t to apply th is technique to a v a rie ty of tropone and tropolone derivatives; th e p resen t pap er describes th e resu lts of these calculations.

T H E O R E T IC A L A P P R O A C H A N D C H O IC E O F P A R A M E T E R S

U sing th e H iickel a, n approxim ation, the hea t of atom isation (AH.,) of a con jugated system can be w ritte n in th e form :

- A H a = 2E,;b + F„b + 2 Ex_h (1)

w h ere E^b is th e bond energy of a p a rtic u la r X—Y a bond of leng th r, E„b is th e to ta l jt b ind ing energy, calcu lated b y a su itab le MO procedure, and E x H is th e bond energy of X—H bond (X being C, N or O). In th e p resen t w ork, E„b w as calcu lated by a SCF MO procedure based on the Pople tre a tm e n t13, in w hich th e F -m a trix is g iven by:

F ii = w i + V* q, (ii, ii) + 2 ^ ) (qj — Cj) (ii, jj) (2)

F ii = Pii — Va p u (ii, jj) (3)

H ere W; is th e valence State ionisation p o ten tia l of the p AO of a to m i and (ii, ii) the corresponding one-cen ter repulsion in teg ra l; (ii, jj) is the usual repu lsion in teg ra l b e tw een AOs of atom s i and j and pfj the corresponding ćore resonance in teg ra l; and q, and p,j a re respectively the jt e lectron density of atom i and th e bond o rd e r be tw een atom s i and j.

The q u an tities W, and (ii, ii) w ere found by th e m ethod of P a rise r and P a r r 14, using th e valence s ta te ionization po ten tia ls of H inze and Ja ffe 13,. T ab le I show s values fo r carbon, py rro le - and p y rid ine-type n itro g e n and ke tone- and e th e r - ty p e o x y g m .

t a b l e i

O ne-center Integrals

Atom or Ion Valence S tate Wi (eV) (ii, ii) (eV)

C trtrtr .T — 11.16 11.13N* tr tr trn ( > N —) — 28.59 16.63O tr 2t r 2trjr ( > C = O) — 17.70 15.23O" t r 2trtr ji ( > O) — 33.90 18.60

The tw o -een te r repu lsion in teg ra ls w ere found as befo re9 12 from the- follow ing expression (cf. O hno10):

(ii, jj) = e2 [rij2 + (R; + Rj)2]"* (4)

2R; = e2 / (ii, ii); 2R, = e- / (jj, jj)w here:

(5)

MO TREATMENT OF TROPONE DERIVATIVES 3

The ćore resonance in teg ra l |3?j w as evalu ted from th e therm ocycle p ro cedure of D ew ar and Schm eising17’18, as ind icated in Eq. (6):

R ' C' R E*b R — C" R "X—Y ----> X—Y -----^ X = Y ------ X = Y (6)

1_______________ __________________ t

(D —D")

H ere R ' and R " a re th e equ ilib rium bond lengths, and D ' and D " the bond energy, of pure XY single and double bonds respectively , w hile C ' and C" are com pression energies eva lua ted from M orse p o ten tia l functions. The jt b ind ing energy (E„b ) is equal to m inus th e jt bond energy of th e X = Y bond s tre tch ed to leng th R and in ou r case is given by the fo llow ing expression:

E„b = qx/Wx + >/4qx (xx, xx)/ + q y/W y + V4qy (yy, yy)/ + 2pxy(3xy +

+ (Qx — cx) (qy — cy) (xx, yy) — ‘/2p xy (xx, yy) — Wx — Wy (7)

F rom Eqs. (6) and (7):

P Xy = / (1 — qx)Wx + (1 — qy)Wy — V4q x (xx, xx) — V4qx (yy, yy) —^Pxy

— (qx — cx) (qy — Cy) (xx, yy) + V*pxy (xx, yy) + D ' — D " — C' + C "/ (8)

In our procedure (variab le fl-procedure10) (3 |j and (ii, jj) a re recalcu lated fo r each bond a t each stage in th e ite ra tiv e tre a tm e n t of th e m olecule w e a re considering. In o rd er to estim ate (3fj w e need to know six q u an tities: R ', R", D ', D ", a' and a"; a' and a" being th e M orse constan ts fo r a CC sigma bond and fo r a CC double bond, respectively . These qu an tities can be estim ated qu ite easily in th e case of hydrocarbons9_n, b u t d ifficu lties a riše12 in th e case of bonds involving n itrogen or oxygen. A p art from th e d e a rth of exp erim en ta l data, double bonds involv ing p y rro le -ty p e n itrogen or e th e r-ty p e oxygen in - volve charged species (e. g. R 2N+ = CR,, RO+ = CR,); n o t only it is im possible to estim ate th e h ea t of atom isation of such ions in th e gas phase, w ith suf- fic ien t accuracy, b u t it is also questionab le if p a ram e te rs de te rm ined in th is w ay can leg itim ate ly be used to describe n e u tra l m olecules such as p y rro le o r fu ran . The p a ram ete rs fo r bonds of th is ty p e w ere th e re fo re de te rm ined from sem iem pirical re la tions betw een bond len g th and o th e r bond p roperties; viz.:

(a) A lin ea r re la tio n w as assum ed (cf. 9— 12) betw een bond o rd er and bond length :

r ;j = F —• Gpjj (9)

(b) A t r a t r ix re la tio n 18 w as assum ed b e tw een bond energy and bond length :

B r = A ln [A + (A2 — D 2),/!] — AlnD — (A2 — D2),/2 (10)

(c) A n inverse pow er šeries re la tio n 18 w as assum ed betw een force constan t (k) and bond length :

k = Cr"2 + Dr 4 + Er# (11)


V alues fo r th e p a ram ete rs A—E w ere found by f ittin g su itab le experim en ta l d a ta and used to estim ate th e qu an tities D, R, and a; the re su lts a re lis ted in T able II.

T A B L E I I

Therm ocycle Data

Bond D"(eV)

D'(eV)

R"(A)

R'(A)

a"(A-1)

a'(A-1)

F(A)

G(A)

CC 5.5600 3.9409 1.338 1.512 2.3177 2.0022 1.512 0.174CN 5.1766 3.3463 1.270 1.448 2.5161 1.9209 1.448 0.178CO 7.1011 3.9987 1.230 1.395 2.1787 1.7870 1.395 0.165

A s b efo re12, w e found it necessary to allow fo r the effects of po la rity of th e 0

bonds link ing d issim ilar atom s (i. e. C and N, or C and O). We assum ed th a t re su ltin g charges (q;) on th e atom s form ing a heteroatom ic bond to be pro - p o rtio n a l to the d ifference in e lec tronegativ ity betw een th e atom s concerned, and the corresponding changes in th e valence s ta te ionization po ten tia ls w ere th e n calcu la ted from th e parabolic re la tion :

Wj = a + bq, + cqs2 (12)

H ere a, b, and c a re p a ram ete rs found b y f ittin g th e valence s ta te ionization p o ten tia ls of a n e u tra l atom and tw o ions derived from it. Table III shows v alues of Wj and (ii, ii) fo r various atom s and bonds, a f te r correction for 0

polarization .T A B L E I I I

O ne-center Integrals A fte r a Polarization Corrections

Type of Bond Atom Ćore Charge W; (eV) (ii, ii) (eV)

1U

C 1.035 — 11.5516 11.3236N 1.926 — 27.4161 16.2842

O II O C 1.100 — 12.2872 11.6786O 0.900 — 16.0190 14.4871

c — 0 C 1.093 — 12.2075 11.6406O 1.814 — 30.5989 17.6709

T h e 0 bond energ ies (E„ ) a re found au tom atica lly in the calcu lation of (3fj b y th e therm ocycle, being g iven by:

E o = D ' — C ' (13)

w h ere C ' is found from the M orse function:

C ' = D ' {1 — exp [a' (R' — R)2]} (14)

T he X—H bond energ ies w ere also estim ated during th e p aram etriza tio n p rocedure; th ey a re lis ted in T able IV.


T A B L E IV

X — H Bond Energies

Bond Bond Energy (eV)

C—H 4.4375N—H 4.0418O—H 4.7700

R E S O N A N C E E N E R G Y

We have đefined9-11 th e resonance energy (EK) of con jugated h y d rocarbons as the d ifference in h ea t of atom isation betw een it and corresponding classical polyene, the la tte r value being found by sum m ing ap p ro p ria te bond energies. This defin ition is superio r to o thers th a t have been proposed, fo r tw o reasons.

F irst, th e q u an tity in w hich chem ists are p rim arily in te rested concerning a conjugated m olecule is no t its s tab ility re la tiv e to some idealized s tru c tu re w ith pure single and double bonds, b u t ra th e r its s tab ility re la tiv e to an open chain analog. Since th e la tte r is a classical polyene, th e q u an tity in question is precisely the one w e have defined as resonance energy.

Secondly, our defin ition is independen t of theory ; fo r th e polyene bond energies could (and should) be estim ated from therm ochem ical data . In o u r w o rk u we have estim ated th e ir bond energies from calcu la ted hea ts of a tom isation of classical polyenes only because th e necessary therm ochem ical d a ta are s till lacking; w hile it is to be hoped th a t such d a ta w ill becom e av a ilab le in th e n ea r fu tu re , th e availab le evidence sup p o rt th a t th e values based on th eo ry are not fa r from the t ru th 19.

This defin ition of resonance energy can be carried over to com pounds con tain ing heteroatom s only if a sim ilar add itiv ity can be estab lished fo r bond energ ies in corresponding classical com pounds. H ere th e s itu a tio n reg a rd in g therm ochem ical d a ta is even m ore d isastrous th a n in th e case of h y d ro - carbons, b u t recen t theo re tica l stud ies20’21 in th is lab o ra to ry seem to suggest th a t the necessary add itiv ity does indeed hold w ith su ffic ien t accuracy. The h ea t of atom isation of classical con jugated com pounds contain ing n itrogen or oxygen and calcu lated by our SCF MO m ethod a re w ell rep resen ted by sum s of ap p ro p ria te bond energies. The values used in th e p re sen t w ork a re lis teđ in Table V.

t a b l e v Bond Energies

Bond Bond Energy (eV)

C—C 4.3499C = C 5.5378C—0 4.1594c= o 7.1575C—N 3.5903C = N 5.1654

6 M. J. S. DEWAR AND N. TRINAJSTIC

R E S U L T S A N D D IS C U S S IO N

The com pounds stud ied h e re are show n in Fig. 1 and th e ir calcu la ted to ta l a and jt b ind ing energies, hea ts of atom isation, and resonance energies a re lis ted in T able VI. Since m ost of th e com pounds are e ith e r s till unknow n, o r have only recen tly been p repared , h a rđ ly any therm ochem ical d a ta are available. Indeed, th e only experim en ta l hea t of atom isation so fa r repo rted is fo r tropo lone22; i t d iffers from our calcu lated value by only 0.056 eV or 1.3 kcal/m ole.

F ig . 1. A to m ic s k e le ta l s t r u c tu r e fo r in v e s t ig a te d m o le c u le s .

T he resonance energ ies in the la s t colum n of T able VI a re in te restin g and su rp rising , im ply ing th a t tropone, tropolone, and th e corresponding n itrogen derivatives, a re non-arom atic. The only com pounds w ith large resonance energ ies are those contain ing benzene or nap h th a len e rings and th e ir re sonance energies are alm ost iden tica l w ith those estim ated11 for the benzenoid com pounds. This conclusion is of course d iam etrica lly opposed to th e c u rren t


T A B L E V I

Calculated Total Energies, Heats o f A tom isation and Resonance Energies

Compound-(Total Energy) (eV) -(H eat of

A tom - ResonanceEnergy

(kcal/mole)- Ercb - E abisation)

(eV)

a-Tropolone (I) 11.8420 33.3665 72.266“ — 0.5Tropone (II) 11.7355 23.4678 67.828” 0.8A zatropone (III) 10.5739 28.7376 69.968 2.8p-Tropolone (IV) 11.9189 33.4748 72.351 1.57-Tropolone (V) 11.9162 33.4765 72.350 1.5a-A m inotropone (VI) 11.9481 32.8390 75.058 0.6p-Am inotropone (VII) 11.9679 32.8258 75.065 0.87-Am inotropone VIII) 11.9497 32.8288 75.050 0.44,5-Benzotropone (IX) 17.9436 48.1617 101.605” 18.73,4-Benzotropone (X) 17.3294 48.1142 100.944 3.42,3-Benzotropone (XI) 18.0038 48.1884 101.692 20.64,5-Bentropolone (XII) 18.0471 52.1574 106.037 17.35,6-Benzotropolone (XIII) 17.4343 52.1139 105.381 2.23,4-Benzotropolone (XIV) 17.4320 52.1152 105.380 2.16,7-Benzotropolone (XV) 18.1071 52.1826 106.122 19.34,5-Naphthotropone (XVI) 23.8694 66.7903 135.035” 28.63,4-Naphhotropone (XVII) 22.9013 66.7694 134.046 5.82,3-N aphthotropone (XVIII) 23.9953 66.8217 135.192 32.22,3,6,7-Dibenzotropone (XIX) 24.2700 66.9211 135.566 40.82,3,5,6-Dibenzotropone (XX) 23.6011 66.8101 134.786 22.82,3,4,5-Dibenzotropone (XXI) 24.2201 66.9055 135.501 39.3

a E x p e r im e n ta l h e a t o f a to m is a t io n f o r t r o p o lo n e is 72.21 eV (R ef. 22)b E x p e r im e n ta l h e a t s o f a to m iz a t io n f o r t r o p o n e , 4 ,5 -b e n z o tro p o n e a n d 4 ,5 -n a p h th o tro p o n e a r e 67.43 eV , 101.44 eV , a n d 135.03 eV , r e s p e c t iv e ly . ( P r iv a te c o m m u n ic a t io n f r o m P r o f e s s o r E . H e il- h ro n n e r ) .

assum ption th a t tropolone, and perhaps also tropone, a re arom atic ,23 an assum ption th a t is strong ly supported by HMO calcu lations7’23; th e availab le Chemical and spectroscopic evidence does, how ever, seem to suggest th a t it is w rong24. Thus tropone very read ily undergoes D iels-A lder reactions25, u n d er n e u tra l or basic conditions, and a recen t s tru c tu re analysis26 of 4,5-benzotropone show s th a t th e bonds in th e seven m em bered ring a lte rn a te strong ly and indeed approx im ate closely to th e values expected for single and double honds in classical polyene (1.46 A and 1.35 A).

The idea th a t tropolone is arom atic arose from its ab ility to undergo facile arom atic substitu tions (e. g. diazo coupling), and its s tab ility to strong acids. These reactions are, how ever, ca rried ou t u n d er basic or acidic conditions w here the com pound ex ists as a sym m etrical anion C7H ,0,~, o r cation C7H 70 2+. B oth these m ust be h igh ly resonance-stab ilized ; th u s th e la tte r m ust approx im ate in s tru c tu re to a d ihydroxy deriva tive of th e arom atic trop y liu m ion. S im ilar reasons apply of course to the s tab ility of tropone in s trong acid, w here it exists as hydroxy tropy lium ; u n d er these conditions th e rin g is very inert. One m igh t add th a t the fact th a t tropone is qu ite strong base m ust


im ply th a t th e con jugated acid has a v e ry m uch la rg e r resonance energy th an tropone itself; th e p a re n t base m ust th e re fo re be m uch less arom atic than tropylium .

The theo re tica l p rocedure9-1'2 used h ere leads au tom atica lly to estim ates of bond leng ths; these, and corresponding n e lec tron densities, a re p resen teđ in d iag ram atic form in Fig. 2. U n fo rtu n a te ly no adequate s tru c tu re de te rm i- n a tio n have as y e t been reported , except fo r th e 4,5-benzotropone (IX)26 and even h e re th e possible e rro rs in th e experim en ta l bond lengths, a re ra th e r large. In v iew of th is, th e ag reem ent be tw een them and our calcu lated values m ust be reg a rd ed as satisfactory . In th e case of tropone and tropolone, e lectron d iffrac tio n stud ies27-31 have lead to th e conclusion th a t th e rings in them a re

1 .0 0 6 9 0 .9 8 5 4 0 .9 8 6 8

1.389 X 1 0 9 4 9 0 ^ > / ] 0 1 9 8

H O1.9988 1.258 *■

( I )

0 .9 4 6 4

1.0092

0 .9 5 9 4

T 0 .6 6 3 0 J 0 .6 4 6 21 .259*—| 1.2 9 5 * 4

0 , .1.4720 ( U )

1.9985

NH1.3658

H O 1.390 X 1 .9990 V o 926 4 1,0314

6*?/fb.6455 1.259 X-

1.4963 (N )0 |TT,

1.4763 ( Y )

0 .9 6 4 3 1.0113

1.00731 .3 6 0 *

1.406* i ? - 9878

H 2N y 5051.9432 1 .260*-

1 .0 0 5 0 0 .9 7 2 0 ,

1 .4 0 8 * /&>, , ’ i 1.357H N - 'L v ' V 1n 2 ^ T O . 9 2 9 4 > 0 .9 5 8 3

1.359 X 1 .3 5 4 *

1 .0 6 3 5 ^ „ caV o .9973

1 .9 5 5 4 \ 0 9 6 3 2 1 0 3 9 2

0 .9 6 6 2

m)1.259 X-

014746 ( M )

F ig . 2. M o le c u la r o r b i t a l d ia g ra m s (b o n d le n g th s a n d c h a r g e d e n s it ie s ) f o r m o le c u le s I —X X I. F r e l i m in a r y d e te r m in a t io n o f t h e s t r u c tu r e o f 4 ,5 -b e n z o tro p o n e ( in b ra c k e t s ) b y X - r a y in v e -

s t ig a t io n f r o m R e f . 26.


1 .4 0 3 8[1.384)1] 0 .9831

1 .3 9 0 8tov. 1.4085 8],

1 .4 6 0 8 [av. 1.4875 8 ] /

> 0 .9 8 8 0 1 .4 0 5 8

[1 .3 8 9 & J/1-0''. 1.44858]

M oil^10'30

0 .9 7 8 0 0 .9770

1.451 8 \ 1 .3 5 6 8 ' 1

^ .0 0 8 91 .4 5 6 8 ,1 4 5 7 8

0.91

0 .9 5 9 2 1.(5113

/ l . 3 9 8 8 \1 .3958 1,394 8

^.016®> )o .8 9 9 3

1 .4 0 0 8 ,1 .4 0 6 8

0 .9 4 0 0

1 .3 5 2 8 I 1.444’8

tov. 1.378 8 ] \ . 0 2 4 8 0 .9534M 5s < ^ 0 6561

•« ? < 7 ^ .o 5 !6 3 6 1 0 .9999 1.261 £ 01 1.48

0 (IX)1 .4 6 6 2

0 .9 8 2 2 0 .9909

) l . 4 0 3 8 ^1 .3 9 0 8 ' 1.3908

0 .9 9 0 6 ^

1.406 8\ l . 4 0 2 8 /

0 .9 9 9 9 )— —--- < 39

0 .9 8 8 0 0 .9 7 5 5

1.3528

0 .9 6 66 )4 9S„ . ft6 ^ 1 . 0 3 0 5

H O 1,3898 [ 0 6 5 2 9 -1 .2 5 7 8

01.4520 ( J E )

1.3568 '1 .0 0 1 9 ^

/1 .4 5 1 8 \/ 1.33 5 6 8

\ l . 0 0 6 0

1 .4 5 6 8 „ 1 .4 5 6 8‘ 1.451 8 /

0 .9 5 0 4

0 .9 6 2 9 r

1.4458

i.ooo8V ^ o ! ! ! , 26,x0

1.4740

OH1.389& -

1.9986 (xm)0.9944

- ,i3548^ , ^ 0 . 9 7 2 6 ^ ~ \ 0 ,9 9 0 8

\ , 4 5 7 8

13908OH.9 9 8 9

(X2)

F ig . 2b

p lan a r w ith average CC bond d istances of 1.40 A; it could no t how ever be estab lished w h e th e r or no t th e bond leng ths a lte rn a te . The rep o rted C = 0 (1.26 A) and C—O (1.36 A) bond leng ths ag ree v e ry w ell w ith our ca lcu la ted values.

If tropone and tropolone are indeed non-arom atic one w ould expect gross d ifference in behav iou r betw een polycyclic com pounds fo rm ed from them by annela tion in various positions32. Thus (IX) and (XI) should be arom atic, th e benzene rings being unaffec teđ by a ttach m en t a t th e polyenoid C5 moiety,.


w h ere as (X) should have a non-arom atic quinonoid stru c tu re . L ikew ise the position of the h y d roxy l p ro ton in annela ted tropolones should be unam bi- guous, one isom er in each case being arom atic and the o ther non-arom atic (cf. (XII) w ith (XIII) or (XIV) w ith (XV). These in tu itiv e conclusions are fu lly confirm ed bo th by the calculations rep o rted here (Table VI and Fig. 2), w hich im ply th a t th e non-arom atic anne la ted com pounds should have low resonance energies and strong ly a lte rn a tin g bonds, and also by the availab le experi- m e n ta l evidence32. Thus none of the non-arom atic tropones has as ye t been

MO TREATMENT OF TROPONE DERI VATI VES 11

synthesized, a lthough a num ber of the arom atic isom ers are know n and a re stable. N ote also th a t th e jt electron d is trib u tio n in tropolone, and arom atic anne la ted derivatives, corresponds closely to th a t expected fo r a classical s tru c tu re w ith localized single and double bonds; th u s th e rt charges on carbon a re close to u n ity and on oxygen close to two. On th e o th e r h an d th e non- arom atic benzotropone (X) show s re la tiv e ly la rg e d e p a rtu re from th is classical p icture , due to the despera te efforts of the benzene ring to recover some a t least of its arom aticity .

SU M M A R Y A N D C O N C L U S IO N S

The m ost im p o rtan t conclusion from th e w ork rep o rted here is th e defi- n itiv e pred iction th a t n e ith e r tropone n o r tropolone is arom atic, in d irec t contrad ic tion to the resu lts of HMO calculations. Since the procedure used h ere has proved un ifo rm ly sa tisfac to ry fo r a li system s w hich p roperties are know n experim entally , its p red ic tive pow er seem s strong; tropone and tro polone th ere fo re seem likely to prove add itional nails in th e coffin of HMO theory , rep resen tin g y e t tw o m ore cases w hen HMO erroneously p red icts non-arom atic com pounds to be arom atic.

We hope th a t th e p resen t com m unication m ay stim u la te fu r th e r experim en ta l w ork to se ttle th is point, in p a rticu la r a syn thesis of (X); though if w e are righ t, (X) should not only be d ifficu lt to synthesize b u t p robab ly im - possible to iso late in v iew of facile polym erisation .

R E F E R E N C E S

1. M. J. S. D e w a r , N ature 155 (1945) 50, 141, 479; 166 (1950) 790.2. a. J . W. C o o k , A. R. G i b b, R. A. R a p h a e 1, and A. R. S o m e r v i l l e ,

Chem. Ind. (London) 1950, 427.b. J. W. C o o k , A. R. G i b b, R. A. R a p h a e 1, and A. R. S o m e r v i l l e , J.

Chem Soc. 1951, 503.c. T. N o z o e, S. S e t o , Y. K i t a h a r a , M. K u n o r i, and Y. N a k a y a m a ,

Proc. Japan Acad. 26 (1950) 38.d. W. v o n E. D o e r i n g and L. H. K n o x, J. Am . Chem. Soc. 72 (1950) 2305.

3. a. W. v o n E. D o e r i n g and F. L. D e t e r t , J. Am . Chem. Soc. 73 (1951) 876.b. T. J . D a u b e n and H. J. R i n g o 1 d, J. Am . Chem. Soc. 73 (1951) 876.c. T. N o z o e, Y. K i t a h a r a , T. A n d o, and S. M a s a m i n e , Proc. Japan

Acad. 27 (1951) 415.4. E. H ii c k e 1, Z. Physik. 70 (1931) 204.5. a. W. v o n E. D o e r i n g and L. H. K n o x, J. A m . Chem. Soc. 76 (1954) 3203.

b. M. J . S. D e w a r and R. P e 11 i t, Chem. Ind. (London) 1955, 199.c. M. J. S. D e w a r and R. P e 11 i t, J. Chem. Soc. 1956, 2021, 2026.

6. L. K 1 a s i n c, Z. M a j e r s k i, and N. T r i n a j s t i ć, Z. Naturforschg. 23a (1968) 192.

7. D. R. B u r n h a m and M. J. C o o k, Tetrahedron Letters 1968, 3771.8. a. E. K l o s t e r - J e n s e n , N. T a r k o y , A. E s c h e n m o s e r , and E. H e i l -

b r o n n e r, Helv. Chim. Acta 39 (1956) 786.b. D. M e u c h e, H. S t r a u s s, and E. H e i l b r o n n e r , Helv. Chim. Acta 41

(1958) 2220.c. E. W e 11 i n, E. H e i l b r o n n e r , and H. L a b h a r t, Helv. Chim. A cta 46

(1963) 2041.d. K. I n u z u k a and T. Y o k o t a , J . Mol. Spectry. 21 (1966) 272.

9. A. L. H. C h u n g and M. J . S. D e w a r, J. Chem. Phys. 42 (1965) 756.10. M. J. S. D e w a r and G. J . G 1 e i c h e r, J. Am . Chem. Soc. 87 (1965) 685.11. M . J. S. D e w a r and C. d e L l a n o , J. Am . Chem. Soc. 91 (1969) 789.12. M. J. S. D e w a r and T. M o r i t a, J. Am . Chem. Soc. 91 (1969) 796.13. J. A. P o p 1 e, Trans. Faraday Soc. 49 (1953) 1375.14. R. P a r i s e r and R. G. P a r r, J. Chem. Phys. 21 (1953) 466, 767.

12 M. J. S. DEWAR AND N. TRINAJSTIČ

15. J . H i n z e and H. H. J a f f e, J. A m . Chem. Soc. 84 (1962) 540.16. K. O h n o, Theoret. Chim. A cta 2 (1964) 219.17. M. J. S. D e w a r and H. N. S c h m e i s i n g , Tetrahedron 5 (1959) 166.18. M. J. S. D e w a r and H. N. S c h m e i s i n g , Tetrahedron 11 (1960) 96.19. M. J. S. D e w a r, Tetrahedron Suppl. 8 (1966) 75.20. M. J. S. D e w a r and N. T r i n a j s t i ć , J. Chem. Soc. A 1969, 1754.21. M. J. S. D e w a r , A. J. H a r g e t , and N. T r i n a j s t i ć , J. A m . Chem. Soc_

91 (1969) 6321.22. W. N. H u b b a r d, C. K a t z , G. B. G u t h r i e , and G. W a đ đ i n g t o n , J.

Am . Chem. Soc. 74 (1952) 4456.23. a. G. M. B a d g e r, Arom atic Character and A rom aticity , U niversity Press, Cam -

bridge 1969, p. 85 and 86. b. R. D. B r o w n, J. Chem. Soc. 1951, 2670.

24. a. D. J. B e r t e l l i and T. G. A n d r e w s , Jr., J. A m . Chem. Soc. 91 (1969)-5280.

b. D. J. B e r t e 11 i, T. G. A n d r e w s, Jr., and P. O. C r e w s, J. Am. Chem. Soc. 91 (1969) 5286.

25. a. S. 11 6, Y. F u j i s e, and M. C. W o o d s, Tetrahedron L etters 1967, 1059. b. S. I to , Y. F u j i s e , and M. S a t o, Tetrahedron Letters 1969, 691.

26. T. H a t a, H. S h i m a n o u c h i , and Y. S a s a d a, Tetrahedron L etters 1969, 753.

27. E. H e i l b r o n n e r and K. H e d b e r g, J. A m . Chem. Soc. 73 (1951) 1386.28. M. K i m u r a and M. K u b o , Buli. Chem. Soc. Japan 26 (1953) 250.29. M. K u b o and K. K i m u r a, Buli. Chem. Soc. Japan 27 (1954) 455.30. K. K i m u r a, S. S u z u k i , M. K i m u r a, and M. K u b o , J . Chem. Phys. 27

(1957) 320.31. K. K i m u r a , S. S u z u k i , M. K i m u r a, and M. K u b o , Buli. Chem. Soc.

Japan 31 (1958) 1051.32. a T. N o z o e, in N on-Benzenoid Arom atic Hydrocarbons, Edited by D. G i n s~

b u r g, Interscience Publishers, New Y ork 1959, p. 339.b. D. L 1 o y d, Carboxylic N on-Benzenoid Arom atic Compounds, Elsevier, Am

sterdam 1966, p. 117.

IZVOD

Račun SCF MO za neke derivate tropona

M. J. S. Dewar i N. Trinajstić

Račun SCF MO je p rim ijen jen na izračunavanje svo jstava osnovnoga s ta n ja (toplina atom iziranja, to ta lna energ ija m olekule, energ ija rezonancije, dužina veze, n-elek tronska raspodjela) tropona, tropolona i njihovih derivata. N ajvažniji zak lju čak rada je st to da tropon i tropolon n i s u arom atske molekule, suprotno ran ijim p redviđanjim a baziranim na HMO računim a. Z načajan je i zak ljučak rada da postoji osnovna razlika između m olekula dobivenih p ripajan jem benzena troponu (ili tropo- lonu) u položaju 2,3- ili 4,5- (to su onda arom atske molekule), ili p rip a jan jem benzena u položaju 3,4- (to je onda ne-arom atska, k inoidna molekula).

C H E M 1ST R Y D E P A R T M E N T U N IV E R S IT Y O F T E X A S

A U S T IN , T E X A S 78712 U .S .A .P r im l je n o 9. k o lo v o z a 1969.

Documents

A SCF MO Treatment of Some Tropone Derivatives*