51'. KLEMPEKER, M. W. CRONYK, A.H. MAKIAND G. C. PIMENTEL
5846
electron densities are expressed in units of the electronic charge. Equation 1 was then used in the reverse direction to calculate the values of ~ ~ J c Hinduced ~by introduction of substituents into the benzyl anion. Localization energy changes were calculated by equation 2.17
+
+
6L = 6Lo 6 q b a b Cra~sss6~s (21 Here, &Lois the difference in localization energ)- bet\rcerl the substituted and unsubstituted reference structures, it1 this case 6-2-CH.c and CsH5CH2-, aud the 6q, are Y
the difference in electron density a t atom r between the unperturbed non-localized and localized structures, IY and V, respectively. a11 localization energies are expressed in (17) Terms in E@,,
were neglected,
ci
VOl. 76
uiiits of b, the C C resonance integral appropriate for a ring bond. Inductive Effect.-Throughout this paper the inductive effect has been treated in the manner proposed in the earlier papers of this series.6 It xvas there shotvn t h a t the inductive effect is of major importance in the electron density method. This is apparent from equation 1, where the terms in powers of & decrease with n,, but the polarizabilities are largest for = r, and generally the less important the farther and are separated, In the localization method the results do not depend greatly on the assumptions made about the inductive effect. This can be understood since again the powers of & decrease strongly with increasing n,, while all the l'on-vanishing 6gs terms are roughly of the Same order of magnitude.
CHAPELHILL,N. C.
above.
[COSTRIBLTTIUN ICRUhl TIIE I1k.PAKI'MI~N r OF CIIEhlISTRI'
AND CHEMICAL E N G I N E E R I N G , U N I V E R S I T Y O F C A L I F O R S I A , BERKELEY]
Infrared Studies of the Association of Secondary Amides in Various Solvents BY
\\'ILLI;llI
x L E . \ I P G R E K , hI.\RSII.iLL
It-. C R O N Y N ,
;iUGUST
H.
b I X K I .\ND G E O R G E
c. P I X E N T E L
RECEIVED JUSE 18, 1954 The infrared spectra of S-ethylacctamide, S-whutylacetaniide and y-butyrolactatn have been measured in the regions 3500 t o 3000 cm.-' and 1700 to 1600 cm. as a fuiictiou of concentration in carbon tetrachloride, and as a function of solvent a t fixed concentration. Significaiit spectral changes are observed with seemingly similar solvents. It is suggested that changes in the spectrum are caused primarily by variation of the polymerization constant with solvent. Evidence is presented for weak hydrogen bond formation betreen chloroform and the carbonyl group of the amide.
The association of amides has been well known for a number of years' and much infrared spectral study2,3has been devoted to these compounds. Yet the conditions under which dimeric association, rather than higher polymerization, occurs arc not well known. It has been clearly shown that the functional groups responsible for the association are the amino and the carbonyl groups by forination of NH-OC bondsY Beyond this point the situation is less clear. For primary amides there is considerable evidence of polymers higher than dimers.1,4,6It has been suggested that secondary amides associate in cyclic dimers, as do the carboxylic acids, and consequently dimeric units should be favored over higher polymers.6 In apparent support of this suggestion are the studies of d-valerol~ctani,'-~ where only dimeric units were found. In conflict with this suggestion is the definitive work of lIizushinia, et al., l U on X-methylacetamide in carbon tetrachloride solutions. The high dielectric constant indicates chain polymers, and the frequency shift of the bonded N H absorption with concentration shows existeiicc o f ( 1 ) E S l . a s s e t t r r , i h r i i i Rrrms , 20, ".io fl!l37), ( 2 1 f a ) A. hf. R u s w e l l , IT' 11. R o d e l i u s h a n d R I . I'
R . I < . Richarcis and 11. \!'
l ' l i n m p ~ u n ,J . ('he!17.
Roy,
'firis
.SOL., 1248
JOURNAL, ( 4 ) 11.J . Cople?, G . 1'. Zelllioeier ani1 C. S M a r v e l , TIIIS 6 0 , 2666 (19381 ( 5 : hT. Dav1e. ; , , i l l I 1 I:. l l , , l I C , , l , 7 Y a r n d a y .SocL 47, 1170 ( 1 n3 1) ((;I 11 1,c~taw.j r , ,iiiiI A I I (;roli1t, .I ( ' h r i i r . i'hys , 21, 1621 (lOd3). (Iieferencc is giveii t h e r e i n t o enrlicr i\
