arising from rotational orientation of the alkoxy groups. The measurements on solutions of decyl alcohol in carbon tetrachloride give critical wave length values much shorter than the high frequency region value tabulated by Brot, Magat and Reinisch.13 I t is reasonable to suppose t h a t the single molecules existing in the solutions are responsible for the short critical wave length, and the viscosities of the moderately dilute solutions in carbon tetrachloride are so much lower than that oi the pure alcohol that the critical wave lengths should be much lower. The critical wave lengths in the highly viscous Kujol solution are much higher than those in carbon tetrachloride, although the increase in critical wave length from one solvent to the other is much less than the increase in viscosity. The general behavior of the high frequency critical wave length of decyl alcohol in the pure state and in solution seeins to parallel that of the alkyl bromide critical wave lengths, l7 in particular, that of tetradecyl bromide, which has been inLVestigated in the same.solventslhas well as in the pure state. li However, the apparent critic.tl wave length values for decpl alcohol are somewhat shorter than would be expected for a molecule of this size and the values oi the distribution coetfcient a are very large, probably as a result of the persistence of molecular association in the solutions. l 3 The seemingly curious absence of any considerable distribution of relaxation times for the low frequency dispersion region of the pure alcohols is fli) E.J . Hennelly, \V. AI. Heston, J r . . and C P S m y t h , THIS 7 0 , 4102 (1948). (18) A. J . Curtis, P. I,. RIcGeer, G. B. R a t h m a n n a n d C . P. S m y t h , i b i d . , 7 4 , 644 (1952). (19) C. P. S m y t h , "Dielectric Behavior and Structure," I I c G r a n Hill Book Co., S e w I-ork, N. Y., I Q Z Z , p p , 80-84. JOURNAL,
[COSTRIBUTIOS FROX THE CHEMICAL
possibly explicable ii the rate controlling process is the destruction of quasi-crystalline complexes by the breaking of hydrogen bonds. In the calculation of the critical wave lengths of dodecyl and tetradecyl alcohol in Table IV the distribution of relaxation times was arbitrarily neglected because of the uncertainty introduced by the probable contributions of two different dispersion regions. The effect of two dispersion regions may possibly account for the large values of the distribution parameters a (Table 11:) given by the Cole and Cole arc plots for cetyl and octadecyl alcohols. The dielectric constant and loss values for t-butyl, octyl and decyl alcohols in Table I1 appear to be fairly accurate, b u t they are too far from the low frequency dispersion region to give information concerning the critical wave lengths corresponding to this region and contain contributions from this region which make calculation of the high frequency critical wave lengths too uncertain for inclusion in Table IV. The values for pure octyl and decyl alcohols have been analyzed in detail elsewhere. "O As previously stated, the apparent critical wave lengths calculated for long chain alcohols from the measurements of dielectric constant and loss in the microwave region reported in this paper must be regarded as approximate because oi the absence oi measurements a t somewhat lower irequencies. However, the results are consistent with the explanation of measurements on shorter chain alcohols by other investigators as in\wlving a low irequency dispersion region arising froin hydrogen bonds and a high-frequency region arising from rotational orientation of the alkoxy groups. ( 2 0 ) G . B R a t h m a n n . P h . D Thesis, Princeton University, l ! l , j l .
PRISCETOS, SE\V JERSEY
LABORATORY, FACULTY
O F SCIESCE, T O K Y O L-NIVERSITY]
Internal Rotation in N-Methylchloroacetamide BY
,%N-IC€IIRO
ICHISHIX\, T.ZTSL-0 NAKAG.~WA A N D TSUNEO -IRAKI
~ I I Z U S H I M A , TAI~EI-IIKO SHIR1.4~OUCH1, IS.\O
~~IY.\ZA\V.Z, ICIIIRU
RECEIVED A P R I L 18,1955 Infrared and Kanian spectra and dipole iiioriieiits of S-nietli~-lcliloroacetalriidehave beeii observed. From the experimental results it has been concluded t h a t in the liquid state the molecules are in both the trans and gauche forms, of which only the gauche form persists in the solid state. I n solutions the trans molecules become less in number with decreasing dielectric constant of the solvent until they become hardly detectable spectroscopically in non-polar solutions and in the gaseous state, Based on these experimental data, a s well as those previously obtained for halogenoacetpl halides and chloroacetonc, the nature of.the hindering potential t o internal rotation about the CH,-CO axis is discussed.
In a series of investigations we have been interested in the determination of the configuration of the polypeptide chain in relation to the internal rotation about single bonds as axes. The present experiment has been rllacie with the object of de. termining the Irlolecular structure ~ . ~ ~ chloroacetamide in order to obtain more inforination on the internal rotation about the CHz-CO axis, which is one of the three internal rotation axes contained in the main chain of polypeptides.
Experimental S-Meth~-lchlor(,acetamide was prepared by adding aqueous sodium hydroxide solution and chlornacetyl chloride tc~ the aqueous solution of methylamine.* T h e reaction product was cstracted with chloroform and the pure sample was obtained u~m distillation, m . p . x". ~ The ~ Raman ~by vh: mspectra. l were - measured in the solid state :it room :lnd in liquid state a t ~ 0 0 .TIle result is show11 in Table I , Saturated aqueous solutio11 of sodium nitrite and carbon tetrachlnride solution o f iotlitie were used as filters in the measurement in the solid state. ~~
( I ) For t h e s u m m a r y see S. RIizushima, "Advances i n Prr,tein Chemistry." Vol. IX, Academic Press, New I'ork. N.Y.. 19.54.
~~~~~~~~
( 2 ) \V
8,lQ 13).
.k. Jacobs a n d 11. Heiriclbergrr. .I.
Bic!
(hc.iii
, 21, I 4 >
INTERNAL ROTATION IN N
X a y 20, 1956 TABLE I
RAMAN ASD ISFRARED SPECTRA OF CICH?COSHCH3 -Raman Liquid 185(3b) 25?(2) 308(3) 395(3j 410(5) SSO(4b) fi27(?) 700(d) 783(8) 7SG(7) S91(6j 925(31 1062(3)
spectraSolid
--Infrared Vapor
spectraQ-Liquid Solid
Assignment b
190(3b)
L
313(3)
L
420(41 583:l) 034(2)
L L I,
M M M
51 763(&)
75S(m)
SQ5(4)
108.211)
1I j i ( 7 b )
1157(2)
1?96(Bb) I289(4b) 1331(6b)
126713) 1290 ( 4j
141 l(6)
141314) 1457(1)
14BOfs)
l451(3b) IXjO(1b)
1500!lb)
1315(s;
125Ofs)
703(s) 786(m) S95(vw) 92'2(w) 1057(u) 107i(w) ll57(s) l24l(m) 125S(s)
132S(w)
ili54(0b) l(j44(5J 1'795(3) .2948(10b) 2953(10) 301'2(4) 3017(3) 3300(1b)
1710(vsl
1413(s) 1441(sh) l530(sh) 1580:~s) l570(sh) lIjOO(vs)
?800(vw ) 292O(m)
?94O(m) 3080iw) 3300(vs)
762(s)
L
890(w) 92(j(m)
L L
iOSd(w) 1127(sh)
L I.
115O(s)
L
1265(s) 1290(m) 131B(vwj 1342(vwj 1412(s) 1449(w)
L L I, L I,
M
l565(vs)
I,
M
1643(vs) I. 2SIO(v~) 295O(m) 3100(w) 3300(vs)
M
M Lf
M
M M
L
3470(w)
vs, very strong; s, strong; m , medium strong; w, weak; L, the less polar form; M , the more polar vw, very weak. form. a
The infrared spectra were recorded in the region 2 to 14 by the Baird spectrometer in the gaseous state a t 180" (path length 4 cm., vapor pressure about 20 mm.), in the liquid state a t 60" (very thin film) and in the solid state a t room temperature (see Table I ) . The change of relative intensity with solvent (carbon disulfide, carbon tetrachloride acetone, nitromethane and acetonitrile) was observed for some absorption bands in a cell of the thickness of 0.1 mm. The concentration in each case was so chosen t h a t the absorption of the stronger band amounted to about 50%. The dipole measurement was made a t 25' in carbon tetrachloride solutions. The apparent moments calculated by the use of Debye's equation from the experimental results a t different concentrations are shown in Table 11. p,
TABLE I1 APPAREKT AhfOMENTS O F CICHsCOA-HCH3 IS CClra Orientation .~ .~.~.
Wt. fraction
0 01422 0089 1 00507 00205
Dielectric constant
2 2 2 2
5223 3673 2949 2559
Density
1 1 1 1
5793 5811 5822 5835
polarization (cc.)
190 141 127 127
Dipole moment
(D) 2 84 2 38 2 25 2 25
The sum of the electronic and atomic polarizations was assumed to be equal t o the sum of atomic refractions (25 cc.).
Discussion The molecule of N-tnethylchloroacetaniide has two axes of internal rotation, CO-XH and CHz-CO. The rotation about the former axis can be expected to be similar to that of N-methylacetamide, which was shown to be in the planar trans form
">-,
CHI
/CHI \H
by the measurement of the Raman, infrared, ultra-
-
I
X
~
2039 ~
violet spectra and dielectric ~ o n s t a n t . ~Actually N-methylchloroacetamide shows absorption peaks a t 3300, 3100, 1650 and 1550 cm.-' characteristic of the trans peptide bond. If this were in the alternative form or the cis form,4the substance would show peaks a t 3200, 3100 and 1650 cm.-', just as in the case of 6-valerolactam. Since there is only one configuration ( i . e . , the trans form) for the peptide bond, the rotational isomerism of N-methylchloroacetamide should be explained with regard to the internal rotation about the CH2-CO bond as axis. As to the internal rotation about this axis, we have studied that of ClCHZ-COC1, BrCH2-COC1, BrCH2-COBr and ClCH2-COCH3.j In all these molecules the X-CH, stretching frequency of one isomer (X = C1 or Br) was found to have a different value from t h a t of the other, both appearing in the frequency region predicted by the normal vibration calculation. From the comparison of the spectra of these compounds with t h a t of N-methylchloroacetamide, the two peaks observed a t 763 and 786 cm.-' can be assigned to the C1-C stretching frequencies. The fact t h a t these two peaks have almost the same intensity in the liquid state and that one of them disappears completely in the solid state shows that there are two rotational isomers in the liquid state agd only one of them persists in the solid state, since only one Cl-C stretching frequency is expected for one rotational isomer. This conclusion is confirmed by the experimental result that in the frequency region below 800 cm.-l we observed ten Raman lines in the liquid state and only six lines in the solid state; we can expect six Raman frequencies in this repion for one isomer: i . e . , CH; one Cl-C stretching, one out-of-plane O=C< v
NH -
and four skeletal deformation frequencies. The solvent effect to be described below provides further experimental evidence for the view stated above. The relative intensities of the bands a t 763, 786, 1241 and 1258 cm.-' have been measured in various solvents. According to the result of our previous measurement the more polar form becomes more stable than the other (or the less polar form) in a solvent of higher dielectric constant.6 The calculated dipole moment of N-methylchloroacetamide depends considerably on the azimuthal angle of internal rotation: 4.3 D a t 0 ' and 30°, 4.0 D a t 60°, 3.5 D a t 90°,2.8 D a t 120', 2.2 D a t 150' and 2.0 D a t 180'. Therefore, the two rotational isomers differ considerably in polarity from each other and we can expect the apparent solvent effect for this substance. In fact the intensities of the bands a t 786 and 1241 cm.-' become weaker with decreasing dielectric constant of the solvent until these bands (3) S. RIizushima, T. Shimanouchi, S. Nagakura, K . K u r a t a n i , M. Tsuboi, H. Baba a n d 0. Fujioka, THISJOURNAL, 72, 3490 (1950). (4) F r o m t h e partial double bond character of t h e C-N bond only t h e lYans a n d t h e cis forms are conceivable as t h e rotational isomers of this molecule. See reference 3. (5) (a) I . Nakagawa, I. Ichishima, K . K u r a t a n i , T. Miyazawa, T. Shimanouchi a n d S . Mizushima, J . Chem. Phys., 20, 1720 (1952); lb) S. Mizushima, T. Shimanouchi, T. Miyazawa, 1. Ichishima, K . K u r a t a n i , I . Nakagawa and N . Shido, i b i d , 21, 815 (1953). (6) I . W a t a n a h e , S. Mizushirna a n d Y . Masiko Sci. P a p . I m l . Phys. Res. Tokyo, 40, 4'25 (1943); Y . Morino, S . Mizushima, K . Kurhtani and M. K a t a y a m a , i b i d ... 18,754 (1950).
~
~
COMPARISON OF
Van der Waals radius of R , -4. PL(COR), D Stability in the gaseous state Stability in the liq state Ptwm
-
Pgaucher
D
THE
TABLE 111 MOLECULES OF THE TYPEC1CH2COR
1.8 0 5 trans > gauche trans = gauche
2 0 2 0
trans
