Spectrochimica Acta, Vol. 25A, pp. 1363 to 1374. Pergamon Press 1969. Printed in Northern Ireland

The vibrational spectra of several ethyl chlorides: CH,CH,CI, CH&D$l, CDJ?H2C1, and CD&D&l* t

FOIL A. MILLER and F. E. KIVLAT Department of Chemistry, University of Pittsburghz and Mellon Institute,

Carnegie-Mellon University Pittsburgh, Pennsylvania 152 13

(Received 23 December 1965)

Abstract-The infrared and Raman spectra of CH,CH,Cl, CH,CD,Cl, CD&H&l, and CD&D&l are reported. Vibrational assignments are made for 71 of the 72 fundamentals of the four molecules. The data resolve some discrepancies between earlier work, but two of the funda- mentals are still uncertain.

INTROD UCTION

ETHYL chloride has been shown by microwave studies to have C, symmetry and to be in the staggered conformation [l, 21. Its infrared and Raman spectra have been measured and interpreted on the basis of this symmetry [3, 41. SHIMANOUCHI has recently made a critical survey of these data and has given a preferred set of vibra- tional assignments [5].

For a study of the torsion in ethyl chloride we had obtained samples of CH,CD,Cl, CD&H&l and CD&D&l (hereafter referred to as d,, t13 and d, respectively.) We have taken advantage of their availability to measure their complete infrared and Raman spectra, because these data should help establish the vibrational assignments of ethyl chloride. There are some disagreements among earlier workers [3-51. The parent compound (d,) was also remeasured to make all the data comparable in quality. The only earlier work on the spectra of the deuterated molecules is a report that the C-Cl stretch in d, is at 656 cm-l [6].

EXPERIMENTAL

1. sam(ples . Ethyl chloride of 99.7% minimum purity was obtained from The Matheson

Company, Inc. The samples of d,, d, and d,, all of 98% minimum isotopic purity, were purchased from Merck, Sharp and Dohme of Canada, Ltd.

* From a thesis submitted by F. E. Kiviat in partial ful6llment of the requirements for the degree of Doctor of Philosophy at the University of Pittsburgh.

t This work was supported by the National Science Foundation under Grant GP-7865. $ To which correspondence should be directed.

[l] R. S. WAUNER and B. P. DAILEY, J. Chem. phys. 26, 1588 (1957). [Z] R.H. SCHVVENDEMIAN and G.D. JACOBS,J.C~~WLP~~~. 36,124s (1962).

[3] L. W. DAASCH, C. Y. LIANU and J. R. NIELSEN, J. CIwn. PFjys. 22, 1293 (1954). [4] G. ALLEN’ and H. J. BERNSTEIN, CCML J. Chem. 32, 1124 (1954).

[5] T. SHIBGWOUCHI, T&es of Molecular Vibrational Frequencies, Part I, Bulletin NSRDS- NBSG, p. 40. NBS 6, Washington, D.C. (1967).

[6] I. V. DEMIDENKOVA, Trudy. Gas. Inst. Prikl. Khim. 52, 157 (1964).

1363

1364 FOIL A. MILLER and F. E. Kr~ra~

Prior to measuring the spectra, these compounds, which are gases at room condi- tions, were twice passed through a 36 in. x 0.4 in. column of Linde 3A Molecular Sieves to remove water. They were then passed through a series of four traps on a vacuum line. The first trap was kept at -23°C with CC&dry ice slush, the second and third at -78°C with CCl,CHCl,-dry ice slush, and the fourth at -186°C with liquid nitrogen. Continuous pumping was used throughout the trap-to-trap transfer. The fractions collected at -186°C were then used.

2. Spectroscopic procedure3

Infrared spectra of the vapors were obtained from 33 to 4000 cm-l with Beckman IR-9 and IR-11 speotrophotometers. A Beckman 10 m variable path gas cell with polyethylene windows was used from 33 to 450 cm-l, and a 10 cm gas cell with KBr windows was used from 400 to 4000 cm- l. Sample pressures were varied from 10 to 250 torr. Spectral slit widths were everywhere less than 2 cm-l, and usually less than 1 cm-l.

Infrared spectra of the solids were obtained with a conventional low-temperature cell fitted with KBr windows and a cooled CsI plate [7]. With liquid nitrogen as the coolant, a thermocouple fixed in the CsI plate gave a temperature of 100°K. An appropriate amount of a deuterated ethyl chloride gas was sprayed onto the cold CsI plate. Annealing the solid films did not change their spectra.

Raman spectra of the liquids were measured with a Cary model 81 Raman spectrophotometer using 6328 A radiation from a 50 mW He-Ne laser. The standard Cary co-axial laser excitation optics were used [S]. The samples were contained in sealed capillary tubes. In this arrangement polarization measurements are only qualitative.

Frequencies are believed to be accurate to hl cm-i in the infrared and to f2 cm-l in the Raman spectra unless the bands are very weak and/or broad. Our Raman values are consistently several cm-l higher than those in [3,4], but we checked the calibration carefully and believe our values are correct.

Figures 1 and 2 show the infrared spectra. The Raman and infrared frequencies and their assignments are presented in Tables l-4. Table 5 summarizes our assign- ments. The frequencies for d, are in substantial agreement with the earlier results [3, 41. The polarization measurements also agree with those obtained by the previous authors [3,4] with but two exceptions: (a) We found the 974 cm-l line of d, to be depolarized, whereas both ALLEN and BERNSTEIN and DAASCR et al., report it to be polarized. (b) We found the 1251 cm-l Raman line of d, to be depolarized, in agree- ment with DAASCH et al., but contrary to ALLEN and BERNSTEIN.

These two measurements were made with a new Spex Ramalog apparatus, an Ar+ 4880 A laser, and a right angle illuminating-observing arrangement. We have confidence in them.

BAND CONTOURS

The principal moments of inertia given in Table 6 were calculated from the geo- metrical parameters obtained by SCHWENDEMAN and JACOBS [2]. These parameters

[7] R.C. LoRD,R. S.MODONALD and F. A.MILLER, J.Opt.Soc.Am.42,149 (1952). [8] R.C. HAWES,K.P.GEORQE,D.C.NELSON,~~~R.BECKWITH, AnaZ.Chem.38,1842 (1966).

The vibrational spectra of several ethyl chlorides

I.366 FOIL A. I~GLLER and F. E. KIVIAT

Lc---I---. I

__----__-____-A___

0

-5:

-8 a0

UO!SS!UJSUOJ_L +UXlJad UO!SS!UJSUOJl lUWJ8d

The vibrational spectra of several ethyl chlorides

Table 1. Infrared and Raman spectra of CH,CH,Cl

1367

~~ Infrared Reman

Gas, 296*K Solid, lOOoK Liquid, 295OK ~i~0nt

cm-l Type Inten. cm-1 Inten. cm-l Rel. Polzn. Inti3Zl.

-

2450.6; (Q) 326 336 (&I 345

964 974 (9) 984 I

~~1016 b 1030 (91

1041 1052 (&I ) b 1081 b

1261 (Q) 1279

1289 (Q) 1298

1322 1340

1360 t&l 1362 1378

1385 t&J 1397

1448 t&l fN1470]

1931

1941 (Q) 1952 2026

2035 2046 f&l 1 2237 (&I 2267 b 2445 2462 2737 2747 2757

II

II s

va

m

V8

vs

l-l+S

m-s

N.O.

X0.

631 636 )

646 651 I

783

969 966 980

1

986 1

m

vs

S

VS

W

1074 S

1248 W

1277 m

1282 1 V8

1291 S

1297 )

vs

1304 m,b

1379 m

1428 m

1463 S

1463 S

2831 w-m

337

659

969

1072 1248

1283

1383

1463

2737

2867

27

100

4

17 1

2

Vl8

P VlO

357

dP ve

?

P VS dP 36

P v7

/ 2 x 646; = 1290 2 x 66X= 1302

974 + 336 = 1310 ?

2 x 677 = 1364

dP v,

dP v6* %4

v4

2 x 974 = 1948

12cil+ 786 = 2037

1448 + 786 = 2234 1289 + 974 = 2263 9 1385 + 1081 = 2466

P ?

1453 + 1379 = 2832 ?

8, m, w = strong, medium, weak; v = very; sh = shoulder; b = broad; p, dp = polarized, depolarized. X0 . = Not observed.

[ f Postulated. * Probably impurity, because identical in d, and d,.

1368 FOIL A. MILLER and F. E. KIVIAT

Table 1 (cont.)

Infrared Gas, 295OK Solid, lOOoK

Rlblllan Liquid, 295’K Assignment

cm-’ TYPO Inten. cm-l 1nten. cm-’ Rel. P&n.

2875 2887 m-s 2873 m 2904

2883 3 P V$ 2889 1 2 x 1453 = 2906 2913 1 1453 + [1470] = 2923

2934 9 P %

2967 7 P Vt

2978 3 VlJ

vs 3019 m 3013 1 V11

Table 2. Infrared and Raman spectra of CH,CD,Cl - - Infrared RaIiltUl Assignment

Gas, 295°K Solid, lOOoK Liquid, 295OK

Rel. cm-l REI. Rel. oIlI-* TYJ?e Inten. Inten. (cm-l) Intan. P&n.

247.7 321 331 340

651 663 670

842 851 863 998

1008 1018

1089 1098 1108

1120 1122 1125 1131

1248 1259 1268 1312 1324

(Q)

(Q) I (Q) 1 (Q) I (Q) i (Q) I Ii1 (Q) 1 (Q) I

N.O.

N.O. 333 21 P

631 636

1

641 650 I

814 816 i

852 857

645

815

852

1001 1004

1067

1089

100 P

3 dp

5 P

5 P

Ll

14 P

8 P

1090

1119

1256 1265

1122

Vl8

Vll

*

VlO

V16

VS

1’7

VI6

V8

V6

1008 + 248 = 1256

? P

The vibrational speotra of several ethyl chlorides 1369

Table 2 (cont.)

Infrared RaIXUUl

Gas, 295°K Solid, lOOoK Liquid, 295°K Assignment

cm-’ TYPO

Rel. cm-’ Rel. Ai Rel. Inten. Inten. (am-‘) 1nten. P&n.

1377 1384 1395

(Q)

1442

1469

(Q)

(Q)

1846 1856 1867

-2090 ~2108

2153 2161 2171

b b

(Q)

-2205 2234 2249

b

(Q)

2268 2272

-2399 2506 2737 2746 2758

(Q) (&I

(Q)

2822 (Q) ~2834 b

2846 (Q)

2879 2886 2894

(Q)

2933 2942 2955

2977 2984 2991 2996 3217 3232 3243

(Q)

(Q)

(Q) (Q) (Q) (Q)

1316 1379

1440 1446 I 1462

\ 1468

2156

2187

2249

2275

2733

2861

2933 2938 I 2974

2991

1381

1439

1457

2086

2154

2187

2208

2249

2271

2738

2865

2883

2900

2934

2978

1

2

3

1

15

2

Ll

4

1

2

2

2

2

13

3

dp

dp

dp

P

P

P

dp

P

P

dp

V4

VI4

V4

1008 + 851 = 1859

1098 + 1008 = 2106

VI

1122 + 1067 = 2189 (ii”) ?

1122 + 1089 = 2211 1384 + 851 = 2235 2 x 1122 = 2244 (A’)?

VI1 ? 2 X 1259 = 2618

?

I 1469 1442 + + 1384 1384 = = 2826 2853 2 x 1439 = 2878 (A’)

V8

1457 + 1439 = 2896

(A”)?

Vt

I VlS

2984+ 232 = 3216t 2984 + 248 = 3232 2996 + 248 = 3244

8, m, w = strong, medium, weak; v = very; sh = shoulder; b = broad. p, dp = polarized, depolarized. N.O. = Not observed.

l Probably impurity, because identiael in d, and d,. t 232 is the torsion, 2 t 1 [ 131.

1370 FOIL A. MILLER and F. E. KIVIAT

Table 3. Infrared and Raman spectra of CD&H&l .

Infrared RanMIl Gas, 295OK Solid, lOOoK Liquid, 295’K Assignment

Rel. cm-l Rel. Ae Rel. cm-l Type Inten. Inten. (cm-l) Inten. Polzn.

188.9 290 301 309 620 631 639

(Q)

(Q) II

(Q) I II

-644 ah

677 ~686

834 839 846 8Sb 864 868 876 926 937 943

1053 1062 1123 1136 1142

b

(Q) vs

(Q) vs

(9) vs

1280 1290 1299 1463 1461 1471

(9) 1

(Q) b

(9) 1

(Q) 1

(Q) 1

2082 2090 2099

2128 2133 2142

2229 2240

(Q) 1

(Q) I

b

(&I

II

l_

II

II

II

II t

Ill

2740 2748 2767 2890 2897 2905 2971 2977 2986 3006

(&I I

(Q) I

(Q) I

(Q)

II f

?

I,

VS

W

W

W

607 612

1

659 663

I

vs 618 100

0 -655 /l

841 S 839 14

877 m 862 6

m+3 1051 8 m-s 1064 8

m 1132 S

936 18

1053 3

vs 1286 8

1131 7

1203 1

1287 1

m 1444 1447

1 S 1466 2

2066 3

m 2081 m

m

VS

vs

21’25 2128

1

2230 2240 2264

m

m 91

2082 11

2103 3

2123 29

2230 3 2263 3

m 2875 m 2885 1

vs

V8

2975 m 2971

3008

6

3016 m /l

N.O.

N.O. 302 24 P

P

P

9

P

dP

P

dP

P

dP

P

P

P

P

dP P

P

P

*18

Vll

VlO

v17 (0

t

T

VI

?

v9

Vl4

v69 v16

v4

es

v7

*Ii

1131 + 936 = 2067

(A’)

v8

2 x 1063 = 2106

VS

1 F.R.

1290 + 937 = 2227

VlS 2 x 1131 = 2262

(A’)

1461 + 1290 = 2761

?

*1

v12

s, m, w = strong, medium, weak; v = very; ah = shoulder; b = broad. p, dp = polarized, depolarized. N.O. = Not observed. F.R . = Fermi resonance.

The vibrational spectra of several ethyl chloridw 1371

Table 4. Infrared and Raman spectra of CD&D&l .

Infrared RlMU333 GM, 296OE Liquid, 296OK Assignment

cm-l Type

Rd. A+ Rd. Inten. (cm-l) Inten. Polzn.

184.2 287 297 306 677 616 622 634 721 749 756

761

776 786 796

893 910

1012 1022 1031

1046 1052 1067 1061 1070 1079 1086

1149 116s 1163 1166 1171

1238 1248 1266

2071 2079 2088 2128 2138

2162 2172 2187

(9)

(Q)

(Q)

(Q) 1 (&I (Q) (Q) (&I

(Q) I

(&I i (9) (9) ) (Q)

(Q) 1

(Q) 1 (Q,

If 299 24

II

W

va 612 100

766 (ah)? 6

II m

II vs

786 8

800 (eh) 6

899 24

973 1

1012 10

1060

sh

1074

1135

1164 m

1161

1197 l

W

1277 1382 1943 2017

w-m

W

W

2071

2120 2138 (sh)

W 2161 2189

6

3

/l

3

4

/l

L.1 1

/l 1

12

20 4

12 12

P

dP

P

dP

P

dP

P

P

P

P

P

P

P

P P

Via

vat

v17

VI0

Ii77 + 184 =

F.R,

v1a

V6 622 + 297 = 919

V16

v7

V14

v6

?

vs

899 + 299 = 1198

2 x 622= 1244

973 + 299 = 12721 78s + 612 = 139’7 (A’) 1050 + 899 = 1949 2 x 1012 = 2024 (A’)

va

2 X 1074 = 2148

VI 1022 + 1164 = 2186 (A’)

F.R.

0, m, w = etrong, medium, weak; v = very; ah = shoulder; b = broad. p, dp = polarized, depolarized. N.O. = Not observed. F.R . = Fermi resonance.

1372 FOIL A. MILLER and F. E. KIVIAT

Table 4 (cont.)

Infrared R~IXl&Ii Gas, 296’K Liquid, 295’K Assignment

Rel. Aii Rel. cm-’ Type rnten. (om-‘) Inten. POlZh.

2206 2216 2226 2234 2242 2248 2263 2266 2272

-2346 ~2352

w

m

w

(Q) w 2230 5 dp VI1 w-m

(Q) I

P m 2241 4 dp VU

I w

(Q) 4 m 2262 2 dp ? w

2299 1 P 2 x 1164~ 2308(/l’) 2315 2 P 1161+ 1164 = 2316 (A’)

VW 2172 + 176 = 2348 w 2172 + 184 = 2366

Table 5. Fundamental vibrations of ethyl chloride-&, -d,, -da and -d,

Species Activity Assignments (cm-i)

NO. Schematic description CH,CH,CI CH,CD,Cl CD&H&l CD&D&l

0’ R(P), IR 1 2

(11 and/or I) 3 4

5 6 7 8 9

10

a” 11

R(dp), IR 12 13

LL) 14

15 16

17 CH, rock 18 CH, torsion

CH, str., sym. CH, str., wig. degen. CH, str., sym. CH, deformn., orig.

degen. CH, soissors CH, deform., sym. CH, weg CH, rook LC str. C--Cl str. C-C-Cl bend CH, str., mitisym. CH, str., wig. degen. CH, deformn., orig.

degen. CH, twist CH, rook

2967 Rp

p 2946 11 P 2942 p 2887 p 2161 1 li 2886 p [~I4701 1469 dp

(-1448) 1124 p 1385 dp 1384 dp 1289 11 P 1008 p 1081 p 1098 p

974 dp 11 851 p p 677 II 663 p

336 p 331 p 3014 2272 dp 2986 2996 dp 1448 dp 1442 dp

1251 dp 1067 R 10369 815

R dp

785.5 -

250.6 248

2977 p

2133 p 11 2090 p 1136p II

1461 dp 11 (1062)

1;;;; II 937 p 631 p 301 p 11

3005 2240 dp 1063 dp

2172 p 2128 p

2079 P II 1165~

1203 dp 10629

1155p 1079 p

1022

p 786 p II 893 p

622

p 297 p II

2248 dp 2234 dp 1062 dp

973 dp R 800 dp R

644 R? 577 189 184

[ ] Post&ted. ( ) Used twice. p = polarized. 11 = ptwellel. Valuea are for the gas phase unless marked R; the letter am Reman frequencies.

are as follows: r(C-C) = 1.520 A, r(C-Cl) = 1.788 8, r(C-H of CH,) = 1.091& r(C-H of CR,) = 1.089 A, <(C-C-Cl) = 111”2’, <(H-C-H of CH,) = 108”30’, <(H-C-H of CR,) = 109”12’, and <(C-C-H of CH,) = lll”36’. The A and B inertial axes are in the plane of symmetry, and the C axis is perpendicular to it.

Although these molecules are actually asymmetric tops, they approximate prolate symmetric tops. NIXON’S detailed study of the 785 cm-l band of do demonstrates this, for the contour is that of a perpendioular band of a prolate symmetric top [9].

[9] R. N. NIXON, S~ectrochim. Acta 9, 69 (1957).

The vibrational spectra of several ethyl chlorides 1373

Table 6. Principal moments of inertia and P-R separation of parallel bands of several ethyl chlorides*

Principal moments of inertia APR (amu-As) (cm-l)

IA IB IC (parallel bands)

CH,CH,Cl 16.13 92.22 102.0 19.4 CH,CD,Cl 21.02 94.71 106.2 19.1 CD&H&l 19.61 106.2 116.3 18.1 CD&D&l 24.76 108.3 120.4 18.6

* The atomic weight of Cl used in these calculations is 35.467.

The expected P-R branch separations of the parallel bands were calculated by the formulae of GERHARD and DENNISON [lo, 111, using (IB + 1,)/2 for the two equal moments of inertia. They are included in Table 6. Bands with a clear-cut parallel contour with well developed P, & and R branches, and with a P-R separation of 18-19

cm-l will belong to species a’. Perpendicular bands can be in either a’ or o”, so these contours are not helpful.

Several of the perpendicular bands possess a rich and orderly fine structure. Examples are 785.5 and 1448 cm-l of d,, 1442 and 2272 cm-l of d,, and 1053 and 3005 cm-l of d,. We did not analyze this structure because it does not provide significant new information.

VIBRATIONAL ASSIQNMENTS

Ts,ble 5 summarizes the normal vibrations and our assignments. The 18 funda- mentals of the ethyl chlorides, all of which have C, symmetry, divide into lla’ and 7a” modes. The a’ vibrations give polarized Raman lines and may have either parallel, perpendicular, or hybrid band contours in the infrared spectrum. The a” vibrations give depolarized Raman lines and have perpendicular infrared band contours. Most of the assignments are straightforward, and only the following few comments need be made.

1. The selection rules are rigorously obeyed, where polarizations or band types could be established, except in five cases where depolarized lines are used in a’. (This is permissible.) (a) For the CH, symmetric deform&ions (vJ of d, and d,, 1385 and 1384 cm-l are used in spite of being depolarized because these are highly char- acteristic group frequencies in the infrared. (b) A similar reason leads to assigning 1469 (dp) in a?, to va, and 1461 (dp) in d, to Ye. (c) In d,, 974 cm-l (dp) has been attributed to the C-C stretch (Q). It hss the expected parallel band contour, and there is no other good candidate for this mode.

2. On the whole there is good numerical agreement between the frequencies of: (a) CH, modes in d, and d,, (b) CH, modes in d, and d,, (c) CD, modes in d, and d,, and (d) CD, modes in d3 and d,. These comparisons help to establish most of the assignments. They also show that most of the modes do not mix.

[lo] S. L. GERHARD and D. M. DENNISON, Phys. Rev. 43, 197 (1933). [ll] IV. A. S. PAUL and G. DIJKSTRA, Qectrochim. Acta 23A, 2861 (1967).

4

1374 FOIL A. MILLER and F. E. KMAT

3. There is one striking case of mixing-the C-C stretch in d,. It ws,s expected around 950 cm-l, but there is no band within 50 cm-l of this. We suggest that it has mixed with the CD, wag (Y,) and been pushed to the abnormally low value of 851 cm-l. In o& both modes are back near their original values in d,. This would account for the strange sequence 974-851-937-893 cm-l in going from d,, to d,.

4. The originally degenerate CH, deformation (YJ of do is postulated as occurring at ~1470 cm-l. The band at 1448 cm-l shows a. cluster of sub bands on the high wave number side that are of considerable intensity, with ~1470 cm-1 as the center. This assignment is supported by the 1463 cm-l infrared band present in the spectrum of the solid, and also by the band at 1469 cm-l in the infrared spectrum of gaseous d,. For similar reasons we believe that 1448 of d, is not only yi4, but also Q.

5. We tentatively assign the 1036 cm-l band of d, to the CH, rock (YJ instead of the 785.5 cm-l band chosen by all the previous authors [3-51. The evidence for this assignment is that d, has a corresponding band at 1062 cm-l whereas it has no band within at least 100 cm-l of 785.5 cm-l. We then assign the 785.5 cm-l band of d,, to the CH, rock (vi,). The assignments for yXB and vi7 are the least satisfactory of the entire lot.

6. The asaignments for the C--Cl stretch (vi&, C-C-Cl bend (Q), and the tor- sion (YJ are absolutely certain. We have studied the torsion in d,, earlier [12]. For all four molecules, transitions between higher torsional levels (l-2, 2-3, . . ,) have

now been observed. The results will be reported in detail separately [13]. 7. In d, the presence of the two polarized lines at 839 and 862 cm-l is a problem.

Only one can be a fundamental. The one at 839 can be explained as 655 + 189 = 844, but it is the stronger of the two and would seem to be the fundamental.

8. Explanations for the sum tones are not as satisfactory as usual.

CONCLUSION

Assignments are made for 71 of the 72 fundamentals of ethyl chloride-d,, -d,, -d, and -d,. All but about 12 of these are reasonably certain. For d, there is still doubt about two of the fundamentals. Our results verify the assignments of SHIUNOUCHI

[5] except for a minor interchange of his v1 and v2 and for rather different choices for

y16 and Ye,.

Note added in proof

F. WINTEER and D. 0. HUMMEL have recently published an assignment for the C-H stretching modes of de which differs from ours. [Spectrochha Acta 25A, 425 (1969).]

[IL?] W. G. FATELEY and F. A. MILLER, Spectrochim. Acta 19, 611 (1963). [13] W. G. FATELEY, F. E. KIVIAT and F. A. MILLER, to be published.