The vibrational spectra of penta-deutero-chlorobenzene

Spectrochimica Acta,1965,vol. 21,pp.1495to 1504.Pergamon PressLtd. Printed inNorthern Ireland

The vibrational spectra of pents-deutero-chlorobenzene* T. R. NANNEY, R. T. BAILEY and E. R. LIPPINCOTT Department of Chemistry, University of Maryland, College Park, Maryland (Received

14 December 1964)

Abstract-The Raman spectrum of the liquid and the infrared spectrum of the liquid and gas phases of penta-deutero-chlorobenzene are reported. An assignment of the vibrational modes which is consistent with the Redlich-Teller product rule and the inequality rule of STEELEand WHIFFEN is proposed. INTRODUCTION THE vibrational spectra of the monosubstituted benzenes have been the subject of several investigations in recent years [l-6]. In view of the considerable interest in the vibrational frequency assignments for these compounds it seems desirable to extend the work to the deuterated monosubstituted benzenes. The vibrational analysis of these compounds provides a check on the assignments previously The vibrational spectra of penta-deuteromade for the related compounds. fluorobenzene have been previously reported [l]. In this paper the infrared and Raman spectra of penta-deutero-chlorobenzene are reported and assigned. EXPERIMENTAL was prepared by the method of BAK, SCHOOLERY and Chlorobenzene-d, WILLIAMS [7] by bubbling DC1 through chlorobenzene in the presence of aluminum chloride as a catalyst. The reaction was assumed to be complete when the C-H stretching bands were no longer visible and no further changes in the spectrum were observed. A gas chromatographic analysis of the product gave no indication of impurities. The infrared spectra of the liquid were obtained in the region 4000-250 cm-l using a Perkin-Elmer 421 grating spectrometer equipped with a low frequency interchange. The vapor spectra were obtained in the region 4000-450 cm-l using a heated gas cell with KBr windows. The Raman spectra of the liquid were excited by the Hg 4358 A line from a low pressure Toronto arc and recorded on Eastman Kodak 103a E photographic plates. A two prism Huet spectrograph, model A II (f/8), with a dispersion of 18 A/mm at 4358 A was used in all the Qualitative polarization measurements were made using the measurements. * This work was supported in part by the U.S. Public Health Service, Xational Institute of Dental Research and the U.S. Atomic Energy Commission. [l] D. STEELE, E. R. LIPPINCOTT and J. XAVIER, J. Chem. Phy8. 33, 1242 (1960). [2] D. H. WHIFFEN,J. Chem.Sot. 1350 (1956). [3] E. K. PLYLER, H. C. ALLEN, JR., E. D. TIDWELL, J. Research Nat. Bur. Standards 58, 255 (1957). [4] M. L. JOSIEN and J. M. LEBAS, Bull. Sot. Chim. Fr. 53 (1956). [5] R. D. KROSS and V. A. FASSEL, J. Am. Chem. Sot. 77, 5858 (1955). [6] R. J. JAKOBSEN, Wright Air Development Division Technical Report No. ASD TR61-722, Wright-Patterson Air Force Base, Ohio, March (1962). [7] B. BAK, J. N. SCHOOLERY and Y. A. WILLIAMS, J. Mol. Spectrosc. 2, 525 (1958). 1495

‘I?. R.

1496

NANNEY,

R). T.

BAILEY and E. R. LIPPINCOTT

method of polarized incident light,. Assignment of frequency values to the Raman lines was made using a Joyce Automatic Recording Microdensitometer, model MK IIIC, and standard techniques. For many of the overtones and combination bands several possibilities exist especially for the higher frequencies. In these cases not all the possibilities are listed.

2500

2000

1500 FREQUENCY

1000

500

(cm-‘)

Fig. 1. Densitometer twcing of Raman spectrum of C,D,CI.

DISCUSSION will belong to the C,, point Assuming a planar structure, chlorobenzene-d, of MULLIKEN [8] in assigning axes, the group. Following the recommendations fundamental vibrations will be distributed among the symmetry classes as follows. In-plane

vibrations

class a,: class b,:

Out-of-plane

11 vibrations, Raman active (polarized) and infrared active (type A, weak to moderate Q branch, band separation 9 cm-l) 10 vibrations, Raman active (depolarized) and infrared active (type B, band separation 7 cm-l) vibrations

6 vibrations, Raman active (depolarized) and infrared active (type C, strong to very strong Q branch, band separation 7-8 cm-l) class a2: 3 vibrations, Raman active (depolarized) only.

class b,:

(81 R. MULLIKEN,J. Chew&.Phys. 23, 1997 (1955).

I800

I600

1400

Fig. 2. Representative infrared spectra of liquid C,D,Cl 4; attenuator speed, 1100; scan time 40 min; suppression

2000

I _

, -

I -

1000

KM-‘)

600

600

400

200

2000-250 cm-l. A. NaCl windows, capillary film; slit program 1000; gain, 4. B. C&r windows, 0.1 mm path; slit program, 1000; gain 5; attenuator speed, 1100; suppression 4.

FREQUENCY

1200

1498

T. R. NANNEY, R. T. BAILEY and E. R. LIPPINCOTT

(lN33Ud)

33NVllRSNVU

The vibrational spectra of penta-deutero-chlorobenzene

1499

Table 1. Observed vibrational spectrum of C&D&l Infrared Vapor

403 8 422 sh, m

Liquid

282 367 398 412 420 430

m m sh, m vs sh, w w

544 “B, c

546 vs 563 w

614 m, C?

618 m

67la,A

669 680 690 707 747 760 800 816 842 865 922

748 m, C

814 m, B? 860 w

953

w

vs w w VW m VW sh, VW m w w VW

959 w 970

VW

RMllEUl

Assignment

182 m 280 w

408 m (P)

591 w 613 VW 642 VW 667 m(P)

~837 ~865

w overlap m (P) 1

956 “8 (P) 968 sh, m

1000 w 1022 1042 1080 1130 1162

sh, m v*, A m w w

1290 w 1315 w 1350 vs, A 1398 m, B? -1550

8

1600 w 2289 s 2297 2925 3062 3235

B VW w w

1038 “8 1080 m 1166 VW 1193 VW 1277 VW 1260 VW 1292 w 1322 m 1346 vs 1367 m 1399 m 1543 9 1563 s 1602 w 1633 VW 2288 8 2294 sh 2299 sh

10319 (P) 1077 VW

~1273

vvw

1545 m 1567 m (P)

2294 8 (P) 1

b, fundementcl b, fundemontcl aa fundamentsl 816 - 420 = 396 a, fundementcl b, fundamentel 1022 - 591 = 431 or 842 - 412 = 430 or 1292 - 865 = 427 b, fundamental 2 X 282 = 564 b, fundamental b, fundamental 1260 - 618 = 642 or 282 + 367 = 649 a, fundamental a2 fundamental 282 + 408 = 690 282 + 420 = 702 b1 fundamental a* fundamental b, fundement,al al, b, fundamentals 6, fundamental a, fundamental 1543 - 618 = 925 or 1346 - 420 = 926 a, fundamental 546 + 420 = 966 or 1563 - 591 = 972 182 + 816 = 998 b, fundamental a1 fundamental 800 + 282 = 1082 1543 - 412 = 1131 618 + 546 = 1164 591 X 2 = 1182? 865 + 412 = 1277 b, fundamental b, fundamental (P) b, fundamental (9) aI fundamental 747 + 618 = 1365 800 + 591 = 1391 b, fundamental a, fundamental 800 X 2 = 1600 865 X 2 = 1277 a, and b, CD stretching fundtnnentels

The classification of the band shapes as A, B or C and the estimrtted band shapes are based on the work of BADGER and ZTJMWALT [9].In these calculations, a planar regular hexagonal structure was assumed with rCc = l-40A, rCD =

l-08A and reel= 1.67A. [9]R. M.

BADGER

and L. R. ZUMWALT,J. Ckm.

Phys. 6, 711 (1938).

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T. R. NANNEY, R. T. BAILEY and E. R. LIPPINCOTT

In addition to symmetry properties very useful in making the assignments. Comparison

with C,D,H,

C,D,

two other approaches were found These will be considered in turn.

to be

and C,D,F

Assignments of these molecules have been made previously and are included for comparison in Table 2. Using these assignments and the inequality rule of STEELE and WHIFFEN [lo] an upper and lower limit for each vibrational frequency can be established. The interpretation of the spectra was considerably simplified using this technique. Comparison

with C,H,F-C,H,CI

and C,D,F

The difference in the observed vibrational frequency for a given mode for the pair CGH,F-C,H,Cl and for the pair C,D,F-C,D,CI should be similar, since in both cases the cha,nge in potential energy is entirely due to the substitution of Cl for F. Exact similarity between the pairs is not expected due to the difference in mass of the two pairs. This relationship was useful in several instances. It should be noted that the success of the listed comparison methods depends upon the validity of previously made assignments. Consequently, whenever it was possible the assignment of the vibrational modes of C,D,Cl was based on other evidence. IN-PLANE

VIBRATIONS

Class ai Eight of the eleven frequencies expected in this class are readily identified. The polarized Raman lines at 408, 667, 865, 956, 1031, 1567 and 2294 cm-l are immediately assigned to the a1 class; and on the basis of the inequality rule and comparison with C,D,F, they are identified as the ring deformation, a mixed ring deformation and Cl stretch, highest C-D deformation, ring breathing, C-Cl stretch, highest C-C stretch and highest C-D stretch, respectively. A strong infrared band at 1350 cm-i having type A contour is assigned to the remaining C-C stretching mode. Other observations tend to confirm these assignments: (1) The Raman lines at 667 and 1031 have corresponding infrared lines in the gas phase that possess type A contours. (2) The most intense infrared absorption should be associated with the C-Cl stretching vibration since it involves the greatest change in dipole moment during oscillation. The strongest line in the infrared spectrum was assigned previously on other grounds to the C-Cl stretching mode. (3) The Raman lines at 865 and 956 cm-l have been assigned to modes derived from the forbidden infrared bands of C,D, at 945 and 970 cm-l (a,,), and consequently would be expected to be only weakly infrared active. Both lines are observed to be weak in the infrared. The remaining two C-D stretching modes are apparently hidden by the strong absorption at 2294 cm-l and are estimated for product rule calculations in Table 2. [lo] D. STEELEand D. H. WHIFFEN, Trans. Faraday Sot. 55, 369 (1959).

1501

The vibrational spectra of penta-deutero-chlorobenzene Table 2. Comparison of vibrational assignments C,H,Fa

C,H,CP

C,D,H”

C,D,D”

C,D,F1

C,D,Cl

-

Approximate description of mode

3065 3049 3036 1692 1492 1219 1156 1020 1009 806 519

(3071) (3050) (3029) 1680 1477 1085 1174 1026 1003 701 415

3050 2291 2275 2276 1664 1341 980 950 859 814 (579)

2293 2276 2275 2266 1653 1330 970 945 869 812 579

2295 (2275) 2270 1578 1389 1163 959 880 817 753 505

2295 (2275) (2270) 1563 1346 1038 959 865 816 667 412

CD stretch CD stretch CD stretch CC stretch CC stretch CX stretch Ring breathing /ICD deformation ,%D deformation Ring deformation Ring deformation

3095 3072 1592 1457

3071 3052 1580 1445

(2288) (2275) 1564 1388

2276 2266 1553 1330

(2276) (2266) 1564 1311

CD stretch CD stretch CC stretch

1324 1282 1155 1065 615 406

1326 1271 1157 1068 618 297

1289 1175 984 840 815 584

1282 1055 869 823 812 579

1281 1035 843 806 590 388

(2276) (2266) 1543 1322 01‘ 1292 1260 1022 842 800 591 282

bt

982 896 752 682 499 242

985 902 740 682 467 196

928 818 711 613 514 367

830 789 664 599 497 351

(825) 717 627 563 438 229

816 747 618 546 420 182

yC!D doformation YCD deformation $D deformation Ring deformation Ring deformation C-X deformation

%

955 831 (400)

965 830 (400)

(789) 664 (351)

789 664 351

(789) 682 350

760 680 367

I/CD deformation I/CD deformation Ring deformation

a1

ba

CC stretch CC stretch fiCD deformation j3CD deformation DCD deformation Ring deformation CX deformation

In this regard the Raman line at 2294 cm-l exhibits definite indications of being formed by overlap of four or more lines. Unfortunately, resolution of these lines was insufficient for assignment of frequency values to them. The remaining a, fundamental, a C-D deformation is predicted by the inequality rule to be in the frequency interval 812 -=c a, -=c 817 cm-l

The infrared band at 816 cm-l

is assigned to this mode.

Class b, The C-D stretching frequencies in this class should appear near 2276 and 2266 cm-l and will be hidden by the strong band in this region. For the purpose of Redlich-Teller calculations both frequencies are estimated in Table 2. Of the three C-C stretching vibrations expected in this class, the highest is assigned to the line at 1543 cm-l by comparison with C,D,F. This assignment is supported by the infrared spectrum which shows a strong band at about 1550 cm-l which has the appearance of a type A band overlapping a type B band. This is 5

1502

T. R. NANNEY, R. T. BAILEY and E. R. LIPPINCOTT

exactly the expected behavior in the vapor phase if the lines observed for the infrared and Raman spectra of the liquid at 1543 and 1567 cm-l are modes of the b, and a, classes, respectively. The assignment of the two remaining C-C stretching modes is the least satisfying in the b, class. On the basis of predicted values of 1299 and 1283 cm-l, the observed lines at 1292 and 1260 cm-l are tentatively assigned to these modes although the line at 1260 cm-l appears to be anomalously low. These assignments are in agreement with the inequality rule which places these vibrations in the regions defined by 1289 < b, < 1311 and 1175 < b, < 1281 cm-l. The closeness of the predicted frequencies for these vibrations suggests the possibility of interaction between the modes. Indeed, this could explain the low value of the 1260 cm-l mode, but if interaction occurs the higher C-C mode may occur at a value higher than the predicted 1299 cm-l value. Consequently, the moderate line at 1322 cm-l becomes B distinct possibility for this mode. No decision appeared possible on the basis of the available data. In C,D,F the three C-D deformation modes of this class occur at 1035, 843 and 806 cm-l. A comparison of C,D, and C,D,F reveals that these frequencies are not particularly mass sensitive. Furthermore, the change in the frequency of these modes for the pair C,H,F and C,H,Cl leads to predicted values of 1024, 845 and 811 cm-l for C,D,Cl. The application of the inequality rule also results in frequencies in these regions. Two possibilities exist for the highest frequency mode, namely, the observed lines at 1022 and 1000 cm-l. The line at 1022 cm-l appears to be the better choice on the basis of the above considerations and also on the basis of intensity considerations. The lines at 842 and 800 cm-l have been assigned to the other two C-D deformations. The ring deformation mode is not expected to change greatly from the value observed for C,D,F with the predicted value being 591 cm-l. The Raman line at 591 cm-l has been assigned to this vibration. The only other line in this region is the weak infrared line at 563 cm-l which has no corresponding Raman line. There appears to be no doubt regarding the superiority of the assigned 591 cm-l line relative to the 563 cm-l line since for all other similar compounds the Raman shift was much stronger than the infrared absorption. The remaining frequency in this class, a C-Cl deformation, should occur at a lower frequency than the corresponding mode in C,D,F at 388 cm-l. This frequency drops 109 cm-l in going from C,H,F to C,H,Cl leading to a predicted value of about 279 cm-l for C,D,Cl. The only band in the expected region is that found at 282 cm-l which is assigned to this mode. OUT-OF-PLANE

VIBRATIONS

Class b, Three C-D deformations occur in this class with the highest expected near 820 cm-l, but all the bands in this region have been previously assigned. The vapor phase band at 814 cm-l has a complete band head contour which indicates band overlapping. Consequently, this band is assigned to both the a, and b, classes. Assuming the ttssignment of C,D,F to be correct gives an inequality rule prediction for the next C-D deformation of 711 < b, < 71’7 cm-l. However,

The vibrational

Table 3. Redlich-Teller Symmetry Class % 4 b1 a2

1503

spectra of penta-deutero-chlorobenzene product ratios

Theoretical

Observed

5.53 5.28 2.68 1.82

5.23 5.36* 2.65 1.7

* Assuming 1322 cm-l for the intermediate CC stretching mode.

there seems to be no doubt the type C band at 748 cm-l belongs to this mode. This indicates that the speculative assignment of the corresponding mode in C,D,F at 717 cm-l is in error. The lowest C-D deformation predicted to be in the region 613 < b, < 627 cm-l is readily attributed to the type C band at 618 cm-l. The highest ring deformation mode is immediately assigned to the very strong type C band at 546 cm-l. The remaining ring deformation, predicted to be in the is associated with the weak band at 420 cm-l region 367 < b, -=c 438 cm-l, although the band at 430 cm-1 remains a possibility. The Redlich-Teller rule favors the assignment of the 420 cm-l line. The Raman line at 182 cm-l is readily assigned to the remaining mode in this class. Class a2

The fundamental frequencies in this class should closely resemble the corresponding frequencies in C,DB and C,D,F. On the basis of this work no definite assignments can be made, but since some relaxation of the selection rules is probable in the liquid, the forbidden bands at 760, 680 and 367 cm-l are tentatively assigned to this class. None of these bands was detected in the vapor phase, although the band of lowest frequency was below the range of our measurements. APPENDIX Since the completion of this paper, a set of force field calculations by SCHERER [12] for the in-plane modes of C,D,Cl has come to the attention of the authors. Agreement between the calculated absorption frequencies and those assigned in this paper is quite good. For the a, class a difference of 3.2 per cent is observed between the calculated and the assigned values for the lowest CC stretching mode at 865 cm-l. For all other modes for the a, class this difference is approximately one per cent. For the b, class the calculations indicate that the line at 1322 cm-l probably should be assigned to the intermediate CC stretching mode. If this choice is made, the calculated and assigned values for the b, class differ by approximately one per cent. [ 111 S. BRODERSON [12]

and A. LaNasETH, Kgl. Danske,Videnskab. Selsknb. Mat.-fys. (1959). J. R. SCHERER,S~~&~~~~WL. Acta 20, 345 (1964).

Skr

1,No.7

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T. R. NANNEY, R. T. BAILEY and E. R. LIPPINCOTT

It is noted that the modes calculated by SCHERER, based on a valence force field, agree better with the assigned values than those modes obtained using a Urey-Bradley force field. This point was stressed by Scherer for a number of other chlorinated benzenes. Acknowledgemnt-The

t,he compound.

authors sre great,ly indebted to Dr. JUSTINHAMERfor preparation of