Vibrational spectra of benzene derivatives—XXI. Benzoyl fluoride, acetophenone, methyl benzoate and related compounds

Speclrochimica Acta. Vol

33A. pp 5X3 lo 587 Pergamon Press 1977 Prmted m Great Brltam

Vibrational spectra of benzene derivatives-XXI. Benzoyl fluoride, acetophenone, methyl benzoate and related compounds J. H. S. Division

of Chemical Teddington,

GREEN

and D. J. HARRISON

Standards, Middlesex

National

(Received 10 June Abstract-The X = F, CH,, of assignment

Physical

Laboratory,

TWI I OLW, England 1976)

i.r. and Raman spectra are presented and interpreted for the compounds C6HS COX, CD, or OCH, and the assignments are related to those for X = OH. Some details for X = 0C2HS, I or NH2 are also presented and discussed.

INTRODUCTION

basis for the assignment. The Raman spectrum agreed with previous work [6] which it extended, but there were significant differences from the i.r. spectrum [4]. There were not confirmed absorptions strong at 1767, 316, medium at 1727, 1210, 875, 675, 507, or weak at 777, 280, 246 cm-‘. If the usual interpretation (eg [7]) be made of the sum-bands (some are overlapped by vg) then the values are: 1976, 2 x (988); 1932, 938 + (988); 1912, 938 + 964; 1772,,938 + 848. Some evidence is thus secured for the, as usual, illdefined vZ6. The assigned values closely parallel those for benzoic acid and provide substantial independent evidence for the interpretation for the latter.

This paper presents for a group of related compounds C6Hs COX, X = F, CHB, CD, or OCHs, vibrational assignments which are consistent among themselves and with that proposed for X = OH [l]. The principal problem is the identification of the additional vibrations deriving from the -COX group, and their location consistent with the mass of X. As always, the intercomparison of a group of compounds in which X is changed in a regular way is indispensable for elucidation of the complete pattern. For benzoyl fluoride and acetophenone wide range (400&5Ocn-‘) i.r. (with band contours) and Raman data (with depolarisation ratios) for purified materials have been utilised. Available data on acetophenone-d, and -da have been incorporated in the exposition, with some changes in their previous assignments [Z]. The i.r. spectra of methyl and ethyl benzoate have been extended and parts of their assignments are considered, as also are those for benzamide [3] and benzoyl iodide [4] in relation to other benzoyl halides

Acetophenone

The present work adds the evidence of i.r. band contours to previous data [2,8,9]. It was thus shown that the predominant intensity of the strong band at 589 cm-’ derives from a planar vibration, rather than from flC0) [2], or E in the present notation. Assignment of the n’ class may therefore be satisfactorily completed with the value 589 cm- ’ ascribed to vZ1. However, whilst the locations of v3,,, vjI are established by the type C contours of the prominent bands at 761, 693 cm-r, no discrete feature is observed for vs2. Reference to the assignment for benzoyl chloride [S] (Table 3) suggests that vJ2 must be above 650 cn- r for acetophenone, and accidental coincidence with v2r is therefore excluded. Weak absorption for the liquid at 667 cm- ’ [9] is not confirmed; presumably therefore v32 remains unresolved from vjI, but some doubt must remain. Since B is the v(C-CH3) mode, most likely it is coupled with the a’ CH, rocking mode; these two mixed modes are plausibly assigned to absorptions at 1099, 955 CIY-~, the latter has a polarised Raman analogue and type B contour. The a” rocking mode

c51. The planar structure C6Hs COX has 25~’ + lla” vibrations and the modes deriving from the -COX group are conveniently designated a’: A, v(C==O); B, v(C-X); C, 6(OCX); D, S(CCX), rocking; a”: E, y(OCX), wagging; and
ASSIGNMENTS

Benzoyl Jluoride

The observed i.r. band contours, or the Raman polarisation data, or both, comprise the experimental 583

J. H. S. GREEN and D. J. HARRISON Table

I. Vibrational

(cm- ‘) for some C,H,

F

OH

Ill

i.r.

3077

1695 1605 1585 1499 1456 1328 I292 1425 1129 1186 1179 1074 1029 1000 808 668 616 551 422 288 985 974 935 856 812 709 685 428 388 190 s. m. W: strong.

assignments

(-3 Raman

3074SlI 3067m 3038rt 1810r.s A 1601s A

3079.x 3065slt 3042.A 1809rs 1601rs

0.16

0.25 0.50

1587m

1492m B 1454s B 1319m 131 Im 1260s 1245s 1180s A 1163~ 1074w 10381~s 10161~s A 766s B 645s A 615m B 487~ hr 316s A 212m

1493w 0.4 1454W 0.5 1319l.W 0.7 1256~1 1240s 1180m 1163m 1075W 1032~ IoOlrs

769r.s 644~ 615s 49ow

0.17 0.15 0.13 0.72 0.32 0.02 0.03 0.75 0.5

376m

0.15

21 IW

0.55

(988) 964sh

9721~ 940rw 848W 797~ 705W 683~ 423~ 403tW 167~s

Y38w 848W 797m C 699s C 681s C 425~ 402~

medium.

weak;

COX compounds

0.57 0.76 0.7

i.r.

Raman

i.r.

Raman

2290 2274

2290 2272

3064s 3035s

3072m p

1684 1562 1540 1374 1325 1294 1038 1074 1228 865 841 831 798 956 698 530 579 461 376

1684 1562 1539 1374 1328 1294 1034 1086 1228 864 841 829 808 954 678 513 588 438 378 204

1722~ 1601s 1582M 1492~ 1454r.s (1315) (1282) 1315m 1277~s 1178~ 1160m 1068m 1024m 1002W 824s 674s 617~ 360s 336s 213m

1722s p 1603s dp

984sh

VW

(990)

974W 926~ 848~ 761~s C 693~s C

816 768 (698) 660 651 579

792 814 757 678 659 633 546

150

213m

3095w 3063m

3066m

0.6

16851,s 1599s 1582s 1491n 1449s 1311w 1302~ 1102w 1266s 1180m A 11598 1078m

1682s 1597s 1586w 1490~ 1450~ 1314w 1302~

0.38 0.56

1264s 1178m 1158m 1074s 1024s 999s 731s

0.28 0.5 0.7 0.3 0.3 0.1 0.1 0.7 0.7

1025m

A

1OOlH 730m 589s B 618~ 468~ 368~ 225m

0.6 0.8

587m

617s 464~ 365w.p

849Wip 762~ 695~

690sh

0.78

OCH,

PI

-d,

428~ 411W 160~

r. very; sh. shoulder:

406~ 165wdp

hr. broad.

A. B. C: band

contour;

1311s p 1277~s p 1183m p Il60m dp 1028m p 1003cs p 824s p 679m

2 13s d/J

968m 938m 85OM 808m

710r.s 688s 479m

p, dp. polarised.

218s dp depolarised.

( ): inferred value.

Table i.r. 3075W 304OW 1717rs 1602s 1585s 1492~ 145lm (1315) (1280) 1315s 12750s 1176s 1160m 1070s 1029s 1oOlw

2. Vibrational

Raman 3072m.

p

1718s, p 16OOs, dp 1489~ 1453m. dp

1305m. p 1272s, p 1176m, p

1162m,dp 1028s. p 1002us, p

assignment

(cm- ‘) for ethyl benzoate

i.r.

Raman

850s 674m 618~

848s. p 675m 618s. dp 333s. p

332m 272m

l93w

185.7, dp

980sh

(973) 935m (850) 808m

710s 688m 497w 420sh

193w

492~ 420~ 185s. dp

i.r.

ix

W,)

6 (CHJ

4 (CH,) CH2 wag v(C---C) v(C--o) CH3 rock 6 cc0 6 cot us1 6, (CH,) CH2 tw CHa rock CH2 rock v(CCG)

p

618m dp 360s p

1465~ 1460m 1396m 1370s

Raman

1397w. p l370m, p

1245sh

1llOas

lllOm, p 78Ow. p

398m 153w 1460m (1245) 875w 780m 118~

87Ow

Vibrational spectra of benzene derivatives-XXI may afford the weak absorption at 1019cn-‘. The alternative identification has been made [lo], both for acetophenone and some p-substituted derivatives, of the a’ rocking mode at 1076cm-‘. Certainly that polarised Raman line is much more intense than for benzoyl fluoride. The remaining CH3 modes are: 2971. v,,; 2922, v,; 2862, 26,,; 2705, 26,; 1433, 1428, 6,,; 1359, 6,. No assignment is made for the CHJ torsion. Revised assignments for acetophenone-d, and -ds, utilising available data [2] have been included in Table 1; it is important that they are now additionally consistent with those for benzoyl chloride-d, [S]. Merhyl benzoate The present i.r. and available Raman [l l] spectra of methyl benzoate support the interpretation proposed for the preceding. In particular, there are wellresolved absorptions at 674, 688 and 7lOcm-’ the first of which has a polarised Raman counterpart identifying ~1~ 1, thus leaving the two higher values of 808 cm- ’ as available for vjO. vjl. Identification the y(CH) mode vZ9 has been made previously [7,12], and evidence from sum-bands, adduced for the value for vZ6 [7]. Prominent features at 1315, 1277cm-’ are too intense to derive solely from v1 1, vL2 which they likely overlap; with another strong band at 1113 cm-’ they comprise three of the skeletal stretching vibrations previously identified in the ester linkage [3]. (A fourth, at 1174 cm- ’ however, is clearly from Table 1, rather to be assigned to v,~.) The three together involve the present B, q and the additional v(O-CH,) motion; the latter is also likely to be involved with the u’ CH, rocking mode. At least formally for the latter is available absorption at 1194 cm- ’ whilst that at 968 cn- ‘, which seems too strong to derive solely from the y(CH) mode vZ7, may be the a” CH, rocking mode. There is an additional planar skeletal bending motion in the ester linkage which will couple with

585

D, f and U. In addition there will be two a” skeletal torsions: of the CHJ and 0CH3 groups. For the three fundamentals there are available absorptions now observed at 169m, 128~ and 68w, cm-‘, for the first two of which there are corresponding Raman shifts of 175, 134cn-’ [ll]. Calculations [14] give the values a’, I33 ; a”, 170, and 100; together with 58 cm-’ for the phenyl torsion. These give detailed information on the forms of the (mixed) vibrations and most of the calculated wavenumbers agree with those in Table 1. Of particular importance for the present work are the values 809, 713 and 688 cm-’ for three a” modes which can be approximately described as involving E, i and (u + E), successively. Remaining CH3 vibrations are: 2993, v,,; 2952, v,; 2908, 26,,; 2844, 26,; 1448, 6,; 1438, 6,. Ethyl benzoate Data on ethyl benzoate are included to show their regularity with the preceding interpretations. The assignment is in Table 2 with the previous notation. Again, well resolved absorptions at 710, 688, and 674 cm- 1 are distinguished by the polarised Raman counterpart of the latter. Weaker absorptions at 780 and 810cn-’ are candidates for vaO but the former alone has the polarised Raman line, leaving the latter for the y(CH) mode (cf. [7, 121). Additional modes of the 0C2HS group are listed separately, but this is strictly unjustified, particularly for the skeletal vibrations. The tabulation identifies all the fundamentals and accounts for all the observed features; more precise identifications and descriptions can only come from calculations incorporating data from isotopitally substituted species. Remaining features comprising the v(CH) modes, i.r. and (Raman) are: 2980s (298Oqp); 2940m (2945s,p); 2908m (2900~); 2875~ (2875~). Benzamide Some revisions of the assignments [3,8, IS] benzamide can be made through its incorporation

for in

Table 3. Part of the vibrational assignment (cm I) for benzamide i.r.

14NH2 A \I Raman

i.r.

AV

14NHZ i.r. A ~3

i.r.

AV

c31

PI

I31

[31

c31

c31

c31

771(2)

63W

620(2) 530(5)

461(O)

987(1) 968(1)

1

PI 773(3)

l4ND2

738sh

559(2)

1

619(l)

606(3) 480(2)

2

478(1)

V28

2 2

i

1129Y v30/ NH2 wag “31 E y32 u “33 Y

c31

923(1)

849(1) 805(S) 791(3) 705(6) 695(6) 412(4)

14ND,

921sh 1 1 1

798(2) 667(2) 717(5) 692(3)

I

586

J. H. S.

GREFN and

D. J. HARRIWN

Table 4. Parts of the vibrational assignments compounds

(cm- ‘) for some C,H,

Cl do c51 1206 875 673 615 505 418 316 194 989 976 (930) 848 717 692 650 418 400 163

COX

I ds [51

tlk

ix. [4]

649 590 498 392 208 185 (812) 787 71x 688 (650) 536 602 392

1200 851 657 618 486 356 260 162 991 970 93x (845) 772 685 629 416 400 158

1200 830 642 614 40x 325 225

the present scheme. The region 6W900 cm ’ is complicated by the presence of the NH2 wagging mode, but it has now been interpreted consistently with the other compounds, and the i.r. spectra for ---15NH2 and -14NDz compounds provide important supporting evidence. The motions A and B will, with others, comprise the characteristic amide, I, II and III vibrations, assigned previously. Mode q is certainly identified by the prominent Raman line [S] at 1146 cm-’ for the crystalline substance. The remainder of the assignment is in Table 3 where the previous notation has been retained to facilitate comparison. (Some more limited i.r. data [15] for the -NH2 and -ND2 compounds, examined in nujol mulls, are in good agreement with that tabulated and resolve the band compound.) In the a’ at 74Ocm- ’ for the -ND2 by class, both vzO and vz4 are clearly recognised prominent Raman lines, and the participation of the N atom in both bending motions C, D is reflected in the appreciable i5N shifts of v2i and vz3. The NH2 wagging mode is now assigned to the band at 791 cn-’ taken as shifting to 667cm-’ for the -ND2 compound. The ratio of these wavenumbers is 1.2 which is to be compared with values of 1.22 and 1.35 for the NH2 rocking, and amide II bands, respectively [15]. Evidently the NH2 wagging motion is not significantly coupled with adjacent modes, the values for which are all close to those proposed for benzoic acid. The only remaining doubt is the reported [S] opposite dichroism of the bands at 705, 685 cm- I which remains unexplained.

Benzopl

Raman

[I61

826 642 607 401 322 223

(160) (990) (970) 932 (845) 764 680 603 408 (400) 160

chloride,

bromide

and iodide

Parts of the assignments [S] for benzoyl chloride and bromide are re-expressed in Table 4 in the present notation, with due allowance for the shifted positions of X-sensitive modes for the heavier substituents. There are obvious candidates for the a’ modes vzo to both of which will the motions B and v19. Y likely make contributions. Similarly the u” modes v30pv32 are readily identified (though proof from band contours is still unavailable) but, compared with Table 1, it is now the lowest of these which is most likely predominately mode E. Extension to the iodide using available spectra [4, 16) is made in Table 3. Some changes in the previous interpretations [4] are made necessary by that for the other halides, and in order to establish a progression of consistent values. If weak absorptions at 1995, 1902cm-’ are taken (cf. [7]) as 2v,,, and v2, + v2sr respectively, then the tabulated values may be inferred for vz6, vz7.

MATERIALS AND METHODS

Benzoyl fluoride (99% by g.c.) was further purified by vacuum transfer, as were the esters; acetophenone was a certified sample from this Laboratory. 1.r. spectra were recorded using Perkin-Elmer 225 and 180 spectrophotometers, and vapour spectra obtained by use of the latter with a 20m folded path cell heated to 80°C. Raman spectra excited (488 nm) by an ionised argon laser (Coherent Radiation 52B) were recorded using a Spex 1401 spectrophotometer.

Vibrational spectra of benzene derivatives-XXI REFERENCES [l] J. H. S. GREEN, Spectrochim. Acra 33A, 55 (1977). [Z] W. D. MROPS and G. ZUNDEL,Spectrochim. Acta %A, 1097 (1970). [3] R. N. KNISELEY,V. A. FA~SEL,E. L. FARQUHARand L. S. GRAY, Spectrochim. Acta 18, 1217 (1962). [4] P. DELORME,V. L~RENZELLIand A. ALEMAONA,J. Chim. Phys. 62, 3 (1965). [5] D. CONDIT,S. M. CRAVENand J. E. KATON, Applied Spectroscopy

UI, 420 (1974).

H. SEEWANN-ALBERT and L. KAHOVEC,Acra Physica Austriaca 1, 352 (1948). [7] Y. KAKIUTI, R. MATSUMURA,M. EGUCHI and R. SUZUKI,Nippon Kagaku Zasshi 82, 830 (1961).

[6]

587

[S] S. WECKHERLINand W. LUITKE, Z. Elektrochem. 64, 1228 (1960). [9] C. GARRIGOU-LAORANGE, N. CLAVERIE,J.-M. LEBAS and M.-L. JOSIEN,J. Chim. Phys. 58, 559 (1961). [lo] M.-T. FOREL,Thesis, University of Bordeaux (1962). [ll] S. CHATTOPADHYAY,Indian J. Phys. 42, 335 (1968). [12] S. YOSHIDA,Chem. Pharm. Bull. 8, 389 (1960). [13] A. R. KATRITZKY, J. M. LAG~WSKI and J. A. T. BEARD,Spectrochim. Acta 16, 964 (1960). [14] P. CAILLETand M.-T. FOREL,.I. Chim. Phys. 72, 522 (1975). [15] S. Y~~HIDA,Chem. Pharm. EuIl. 11, 628 (1963). [16] E. HERZ, L. KAHOVEC and K. W. F. KOHLRAUSCH, Monatsh. Chem. 74, 253 (1943).