Vibrational spectra of benzene derivatives—XV

Vibrational spectra of bemene derivatives-XV !l!he dimethylphenols, 2,6-, 2,53 and 3,44ichlorophenol J. H. S. GREEN,D. J. H~RISON and W. KYNASTON Division of Chemical Standards, National Physical Laboratory, Teddington, Middlesex (Eec&e.d 10 December1970) Al&r&-The i.r. (366~50 em-l) and F&man speotra of the six ~e~ylpheno~ (xykmols), and the infmred spectrum of 2,6-, 2,5- and 3,~-~c~o~phenol, are reported and interpretedwith the aid of the i.r, spectra of the 0-deuterated derivatives of four of the compounds. Values are proposed for the majority of the fundamental vibrations of the nine compounds.

IN THISpaper are presented the results of an investigation of the vibrational spectra, of the six dimethylphenols (xylenols) and of 2,6-, 2,5- and 3,4dichlorophenol. Infrared spectra (3650-50 cm-l) of these compounds in the solid, liquid snd solution states have been measured, together with the Ramsn spectra of the dimethyl compounds as liquids or ssturated solutions. The interpretations were made utilising the results of previous studies of several trisubstituted bezenes [I, 21 and monosubstituted phenols [3]. With the aid of these end of additional infrared spectrrt of the O-deu~r&~ derivatives of four of the compounds, the majority of the f~d~rnen~~ of all the compounds could be located without ambiguity. Acco~~gly, in the following presenta%ion the discussion is confined to consideration of some dif&ulties which arise with the interpretation, and to the identification of the OH in-plane, 6(OH), and out-of-plane (torsional), y(OH), bending vibrations. All the tabulated i.r. data relate to the monomeric phenols in the dilute solutions state, the Raman data are for the liquids or saturated solutions, as indicated. 1. DIMETHYLPHENOLS

The assigned fund~ment&~ are given in Table 1, apart from those pr~cip&lly associated with the OE and CH, groups wbioh are given in T&ble 2. A molecular symmetry of C,, is a sstisftotory basis for the presentation but, as for l-fluoro-3,5dimethylbenzene, the interpretation is facilitated by relsting the fundamentals to those for X,3,5+imethylbenzene under D Blisymmetry [l]. The e’ and e” fundamentals of the latter, the degeneracy of which will be lifted in 3,5dimethylphenol, can be recognised in Table 1. Thus, there sre two prominent i.r. bands at 1103 and 1149 cm-l of which the latter is the stronger: the polarisation of the Ram&n lines establishes that the former is the 4 component of the e’ vibration at 1164 cm-’ for 1,3,5 trimethylbenzene; the [I] J. H. S. C-X, D. J. J~~~RISON and W. K==~oN, S~~~~. Acta87A,793 (1971). [Zj J.H. S. GOES, D.J. IIaaarso~ and W. Km-ON, S~t~~~.A~ 2?A,807 (1971). [3] J. H. 5. CREZES, D. J. RaaRrso~ and W. KYNAST~N,S~ectroc?G~.ActaWA, 2199 (1971). 3

33

J. H. 8. GREEN, D. J. HARRISON and W. KYNASTON

34 Table

1. Wavenumbers (cm-l) of the fundamental vibrations for 3,6&methylphenol; trimethylbenzene; and l,-fluoro-3,5&methylbenzene

X*

n.(cf. f41)0

2034 3024 1694 1473 1320

a1 Vl Vl V6 V6 V6 V6 VT V8 vB

3019

1317p 1161p 997p 949 678p 680dp 274

1163 1000 960

VlO Vll

aa

OH

1.r.t

622 274

VI, VI4

b1 ~16 VI6 Vl? VlB V19 VI0

b, VII VPS VI: %6 v66 VI6 V67 VI6 VI6 VI)6

1.r.%

R% 3020

3017 1613 1472

930 616 276

276

(636)

(6361

1616 dp

1438dp

183

881 843 677 674 249 138

224

3028 1624 (1449) 1291 1263 1166 926

3017

1613 1472

(1290)

607dp

(1260) 1166 930 617 (4961 276

1309 p 1007 p 948 661 p 616 dp

278

(966) (630)

224

1164 930 617

492 301

276

R% 3062 3030 1692

273

880 836 686 242dp 193

F PI

3067 3028 1690 1473 1306 1131 1008 946 667 614

1299 1164 997 p 930 679 617

1166

226 dp

870 827C 683C 632 263 189 3024 1618 1443 1311 1287 1149 946 608 492 306

CH, PI

880

(870) (630)

VI2

1.r.%

1,3,6-

233

263 3030

1160 607 306

* X in 1, X-3,Sdimethylbenzene. t Dilute solution. $ Saturated solution in methanol. 0 Liquid. ( ) inferred value; C, band contour of vapour speotrum; p, polarised; dp, depolarised.

band

at 1149 cm-l

benzene

the Raman

is then data

attributed were

to the b, component.

inconclusive

[l]

and

(Por

the present

l-fluoro-3,5-dimethylresults

suggest

that

for us and yzs for that compound in Table 1 might be interchanged.) Similarly, there is a shoulder at -950 cm-l on the band at 946 cm-l with which the Raman line at 949 cm-l is evidently coincident and is thus taken to identify the a, component of the e’ fundamental at 930 cm-l for 1,3,5-trimethylbenzene. The band at 946 cm-l is then attributed to the b, component. (Assignment of this absorption to an en vibration [5] is erroneous.) A third pair of bands at 522,508 cm-r is assigned to rn,(al) and ~a&,) derived from a third e’ fundamental. The a, y(CH) mode is taken to be coincident with the b, mode affording the absorptions at 870 cm-l, since the combination bands follow the usual pattern [l]1652: 2 x 827(8,); 1712: 827 + (870)(A,); 1735: 2 x (870)(&)-andprovideno the

values

[4] K. W. F. KOHUWJSUH,Monatah. 76,213 (1947). [S] D. H. WH~~PBIN, Spectrochillz. Acta; 7, 253 (1955).

Vibr&tio~

tspectfaof bemxme deriv&ivea--XV

Table 2. Wavenumbers (cm-l) of the OHfOT)) and CH8 fundamtmti IBOZIEG

Lr.

v (OHI 6 K-W Y (OH)

3.6

3816 1187 310

R.

Ix.

f&8

8624 1104 298

R.

1.r.

2,3

2,3(OD) 8,4 1.r. 1.~. R.

R.

3602 1176 298

for the dimethylphenols*

295 1.r. R.

I.?.

2.4

R.

2,4W') Lr.

2seq 020 233

3617 1188 298

3616 1179 293

3602 1133 301

2867t 062 226

2970

2067

2979

2971 2971

2968

2938 2919 2367 2728

2936 2949 2913 2918 2926 2368 2861 2731 2733 2738 1481 1481 1454 1336 1383 1381 1373 1376 1006 999

2947 2946 2918 2919 2920 2865 2869 2736 2733 2736 1462

2940 2916 2867 2730 1484

1381 1381 1373

1377

1012 983

1010

v,(CH,) &?&H,) ~*~CH~)

2976 2973 2977 2988 2970 2943 2943 2916 2919 2918 2924 2918 2922 2868 2865 2861 273‘1 2736 2743 2732 2739

Lc=J

1443

&(CHa)

1376 1378~ 1381 1381 1385 1334

1380

CH, rook

1042 1042 1021 1022 1019 1023 1000 990 1027 987 985 901 912

1017 986

v&=,)

36

1447 1444 1446

900

* Dilute edution values in carbon tetrechloride. t Diluta eolutionvslusainoerbondisulphide.

evidence for another Take. A prominent Raman line at 225 cm-l certainly identifies r14(a& and although there is very weak absorption at 226 cm-r there is no evidence in either spectrum for the location of Q, whioh may be obscured by Q. Strong absorptions at 1349, 1240 and 1220 cm-l for the solid compound are removed on dilution, and in dilute solution an entirely new band is observed at 1187 cm-l. The latter is therefore reliably assigned to the predominately S (OH) mode for unassociated molecules. This motion is likely also to contribute to one or both of Y,, and ,$(i. Absorption attributed to y30is observed at 312 cm-l for the solid compound; it becomes a shoulder at 305 cm-r on the new strong band at 310 cm-l for a cyclohexane solution, and in benzene aloution is clearly resolved at 306 cm-r since the broad absorption is displaced to 37’6 cm- I. This behaviour identifies the y (OH) vibration (of. [3]). In the i.r. spectrum of the solid the latter vibration affords broad absorption ~720 -l with shoulders at 736 and 705 cm-r. The far infrared spectrum of the solid ~~~bi~ absorptions at 364, 338; 312 (Q); 279 (Q); 247 (Q, rla); and at 124, 129 and 104 cm-l amongst which the Y(OH. . .O) vibration [3] will be involved. There remains a moderately strong i.r. band at 846 cm-l for which there is no reasonable assignment as a fundamental; it may arise from 274 + 582 (B,). 1.2. 2,6-dimdhylphend In 2,6dimethylphenol the OH group is coplanar with the ring [S] and presentation of the fundamentals is satisfactory in terms of C,, symmetry as, in Table 3, where comparison is made with those for 1,2,3_trimethylbenzene and [S] IL TJ.INGOLQ, Cm. J. Gfsem.a,1092 C&m 89%471 (1961).

(1960); K. U. INGOLD aad D. R. TAYLOR,

Can. J.

J. H.

35

8. GBEEN,

D. J. HARBISOS

and W.

KYNASTON

Table 3. Wavenumbers (cmwl) of the fundamental vibrations for 2,5- and 2,3-dimethylphenol; I,t,t-trimethylbenzene and l-fluoro-2,6-dimethylbenz6no

x,

Y,

.z*

a1 Yl VII VI V4 VS Vi3 V? V8

VS VlO 41

a,

VlS

OD, CH,. CH, 1.r.t

3066 3040 1681 1469 1273 1208 1092 814 669 496 271

3066

3071 3046 1698 1479 1267 1222 1087 826 669 496 286

892

3046 1694 1478 1265 1090 831 669 496 257

236

964

Vl!J

761

766

960 774 767

729 615 32611 149

732

706

%3

VlO %O

3027 1616 1433 1324 1283 1162 1102 663 476 226

1274 1092 816 676

1271 1194 1090 814 668 494 276

1x.$

323 3018 1611 1426 1324 1283 1166

3031 1614 1446 1309 1293 1168 1063 642 476 234

664 478

Rt:

3070 3040 1690 1476 1249 1193 1091 813 667 486 310

3076 3044 1699 1477 1249 1190 1094 811 668 486 318

890

1614

1070 646 486

IsI

3072 3062 1691 1481 1272 1194 1097 817 661 494 283

(630) 232 963

763

766

706 (600) 321

714 613 614 270 (140)

719 642 303 148

3026

3020 1690 1689 1446 1446 1270 1263 (1249) 1163 1166 1077 1073 639 640 468 459 270 274

3036 1624 1470 1313 1260 1162 1081 661 473 272

1306 1297 1162 1072 642 473 (233)

3077 3062 1690 1481 1270 1192 1096 818 662 494 284

890

960

774 767 604

CH,, F, CH,

I.?.$

(630) 230

236

vu

v17

3036

CH,. CH,, ‘JH,

(892)

892 (630)

VI, VI4 b,

OH, CH,, CH, RN. I71)# 1.r.t R(cf. [7])9

CH,, OH. (Da 1.r.t

149 1626

660

* In l-X-2-Y-3-2 benzene. t Dilute solution. $ Liquid. ) Saturated solution in methanol. IISolid.

l-fluoro-2,6-dimethylben~ene [l J. This comparison also facilitates the identification of the CH8 rocking modes, the proposed values for which are in Table 2. The strong, broad absorption at X203 cm-f for the solid compound is sharper for dilute solutions and is shifted slightly to 1194 cm-l: the latter is assigned to 8 (OH) for the unassociated molecules. This motion may also be involved in vea(b,) in view of the rather high value and high intensity of the band at 1324 cm-l. (Other broad bands at 1337 and 1240 cm-l for the solid are absent from the spectra of dilute solutions and must derive from associated species.) The position of yIS(b,) is not certain: if it is ~300 cm-l it may be obscured by absorption due to y (OH), although these two out-of-plane fund&mental6 are unlikely to be very close together. For the solid compound a weak band is observed at 326 om-l which is probably due to vIo. (Absorptiona at 320 om-l has been reported for the the liquid [8] but assigned to y (OH),) l?or the solid ~orn~und the y (OH) mode gives rise to a broad abso~tion [?J

A. DADZEU, A. Po~~RA=

and K. W. F. KOEUZUJSCE, MOM&&.

SO, 253 (1932).

Vibrational spectra of benzene derivatives-XV

37

~700 cm-l; the attribution of another band at 480 cm-i (observed here at 485 cm-l) to the same mode [8] is an error, since on dilution this shifts only to 476 cm-l and is certainly due to Q, (b). For dilute solution in c&ohexane y (OH) is at 298 cm-l. (The value 295 cm-1 for the compound in a polyethylene matrix has been reported, assigned to y (OH), and con6rmed by a shift to 2 19 cm-l for the -0D compound [8] .) In benzene solution y (OH) is displaced to 328 cm- l. The rather broad absorption for the solid at 164 cm-l is that previously reported [8] at 170 cm-l and which, with another band at 87 cm-l, has been ascribed to P (OH. . .O). In dilute solutions both these features are absent and a new weak, but sharp, band arises at 149 cm-l which can be reasonably assigned to yzo (b,). In dilute solution a doublet is observed at 838, 825 cm-l: if yls has been correctly located ~326 cm-l, then the doublet could arise from 326 + 515 (A,) interacting with Y,,. The remaining combination bands are-1652: 761 + 829 (B,); 1778 : 2 x 892 (A,); 1840: 829 + 954(&); 1904: 2 x 954 (A,); 3100: 1479 + 1616 (B,). 1.3. 2,3-dimethylphenol

Clearly the symmetry of 2,3_dimethylphenol can be no higher than C,, but the spectra are found to show close similarity to those of the other compounds in Table 3 and it is convenient to present together the corresponding fundamentals. Two isomers can exist for this compound depending on whether the hydrogen of the -OH group is oriented towards, or away from, the o&o-methyl group. This could lead to the observation of doublets for some of the fundamentals (cf. [3]) and is believed to be the explanation of that observed for a dilute solution at 774, 767 cm-l and assigned to the “umbrella” y (H) vibration. However, shoulders at 1215 and 1154 cm-l could arise from 542 +669 and 496 + 669 interaction with Ye (1208 cm-l) and rz8 (1158 cm-l) respectively, and are not necessarily attributable to a second isomer. Comparison with the i.r. spectra of the other compounds in Table 3 suggests that the absorption at 1176 cm-l for a dilute solution, arises from the d (OH) vibration. Although it is a relatively weak band to have this explanation, the assignment is established by the spectrum of the -0D compound in which that band is absent and a prominent new absorption is observed at 920 cm-l. A strong band at 296 cm-l (cyclohexane solution) is displaced to 380 cm-lin benzene solution; the shift to 233 cm-l (cyclohexane solution) for the -0D compound establishes that these features arise from y (OH). The combination bands are-1655: 767 + (892)(B,); 1720: 767 + 950 (A,); 1896: 2 x 950 (A,). The remaining dimethylphenols have the 1,2,4 pattern of trisubstituted benzenes and the fundamentals have values similar to those for 1,2,4-trimethylbenzene and l-fluoro-2,4dimethylbenzene [2], as shown in Table 4; the remaining values are included in Table 2. 1.4. 3,4-dimthylphenol

For this compound a strong band emerges for dilute solutions at 1188 cm-l which is entirely absent from the spectrum of the solid; it is accordingly assigned to b (OH) [S] R. J. JAKOBSENand J. W. BRASCH,Spectrochim.Acta 81, 1763 (1966).

J. H. 8. GREEN, D. J. BARBISON

38 Table 4.

X, Y, .?I*

a’

(cmex) of the fundamental vibr&ions for 3,4-, 2,& and 2,4-dimetbylphenol; 1,2,4-trimethylbenzene; ad l-fluoro-3,4-dime~y~~~ena

CH,, CH,, OH CH,, OH, Cn, OH. CH,, CH, 1.r.t R(of. [7])$ 1.r.t R(of. [?-j)t: 1.r.t R(of. [7])# 3063

Vt V, 14 VS V4 VI Vk VP

1624 1693 1507 1430 1290

So Vll

1150

1210

1114 1020 945 VlS 748 Vlk 729 665 VlT 436 Vlil Vlv10 461

Vll VI8 Vl4

ho

213

V81

I

3025 1617 1690

3029 1622 1587

1501

1527 1413 1291 1277 1229 1148 1110 1039 932 752 723 667 496

1291 1265 1207 1156 1115 1023 948 752 734 557 491

469 314 221

934 865

307 223

3032 1587

1276 1229 1119 1030 934 769 723 571 609 448 310 230

700 575

446 336 269

33s

708 582 449 330 237 146

3009 1615 1594

1151 1097

1038 929 769

1037 933 772

719 870 487

721 574 490 448 348 207

345 207

Rg

1292 1260 1227 1150 1128 1010 905 763 718 563 484

1618 1677 1510 1452 1291 I246 1211 1166 1125 1021 922 745 717 553 471

347 206

285 209

1622 X682 1448 1287 1246 1209 1152 1126 1023 926 746 717 554 472 439 286 210

943

877

815

699 672

145

3019 1616 1602 1508 1408 1323 1267

802 710 556 443 320 276

CH,. Q&, CH,

I.r.5

CH,, CH,. F 1.r.g

R(C

3040

3034 3016 1620 1600 1511 1415 1323 1264 1231 Ii60 Ill5

876 802

1.r.t

936

932 866

813

oD. CH,. C-n,

3048

865

799

of

W. KYXAWEON

w8Venumbers

Vl

+ t $ $

and

872 813

812

800 710 562 443 312 273

292 (145)

1624 1616 1593 1596 1507 1412 1276 1254 1188 1150 1106 1023 948 746 720 551 485

1505 1276 1254 1189 1151 1106 945 746 719 547 482 4446

312 214

212

932

873

872

862

806

806

809

703 53s 434 310 237 146

695 567 461 343 312 145

343 310 149

fn 1.X.2.P-4.Z-benzene. Dilute solution. Mxxrrtted solution in methanol. Liquid.

unassociated

Another

baud

molecules. at

1210cm-l

A

shoulder

persists

on it st through

1178 cm-l can arise all the

spectra,

snd

from

451 + 729.

is assigued

to 9t1,,

748, the analogue of a sum-level observed for ~-fluoro-2,4-dimethylbe~ene [Z]. The prominent band at 1156 cm-r for the solid and concentrated solutions is resolved into components at llEi8, 1160 cm-l in dilute solution: these are interpreted 8s yI1 with which 2 x 572 is interacting. For c~clclohexanesolution, a broad band was observed at 296 cm-l where there is no absorption for the solid; it can be reliably assigned to y (OH), but its presence confuses the precise location both of v~,, (a’) and rzg (a’) about which some doubt must remain. The firat of these may give the weak Raman line at 314 cm-l, with which a shoulder at 312 cm-l in the i.r. of dilute solutions may oorrespond; whilst rBg,expected at a somewhat lower wavenumber, may be a similsr shoulder at 269 cm-l (Although there is a band at 234 cm-l for the solid, this is absent from the solution spectra.)

whilst

additional

absorption

for the solid

only

is &ttribu~d

to 451 +

A very weak Barn&n line a&145 em-l is in the expected position for +, (a”), but no corresponding ix, absorption cotid be observed, In the spectrum of the solid, absorptions at 167, 146 and 108 cm-l which are absent for solutions are likely to involve the Y (CH. * .O) vibrations. Only one of the CIIs rooking modes, that at SO04on+, can be uniquely identified; it is possible that another is coincident with *I8 at 1920 cm-l. The highest y (CK) vibration ysz is identtied as a shoulder at 934 cm-r on the absorption due to the a” fundamental at 946 cm-l, but some special features arise eonowning Pm and F% which are to be expected ~865 and 8E9 cm-l respeotiveIy. uud bands at 859, 863 and 319 am-2 become in dilute solution For the solid co in this region are eerf;iio paimPat 866,844 tand 811,799 m --l. The f~damen~~ tainly of species a* and any sum-levels ~~~~~t~~ with them to give the doublets must also be A” and arise from unlikely (tc’ + o’) e~m~mation. Further, there are no numerically a&sfaotory sum-levels available (apart possibly from 336 -t_486). Accordingly the pairs of bands are assigned to lrssand var, respectively. &me in 3,4dimethylphenol one CHs group is meta- to the -CH group, the splitting of the y(OH) modes parall& that observed for other m-substituted phenols and is attributed to the forms diRering by the orientation of the CH group coplanar with the ring. The combin&ion bands are accounted for~yth~~~aum-leve~l~22 : 934 + 799; 1748:Sll+ 934; 184f:729 j-1114; 1865:2 x 936,

la5.~~~~~~~~~~~~~ Aa for~-tmmI [3,6j only one v(OH) a~so~~ion for u~~i~~d species wss observed, at 3616arl for dilute solution in es&on tetrachloride. The essentially 6(CH) vibra%ion is ctlearly recognised as the prominent band which emerges at 1171cm-l for dilute solutions ; in this region there is only weak absorption for the solid, which can arise corn 448 + 723, (A’) a sum-level which will also account for a shoulder at 1170 ~rn-~ observed for dilute solutions. Absorptione at 13OQ,1309 cm-r for dilute solutions, of intensity only slightly less than that at 1291. cm--l which is assigned to vgtmust arise from A’ sum levels intera&ug with the latterSand 449 + 866,667 -+ 723, $82 f 768 areavailable, Howe~er~ it is not clear why the ~~es~n~g levels for 3~4-~e~hylphenol, for example, do not give rise to similar observed fatures for &batmole~~e. Another doublet srisiug for ~~~ia~d mole&es is at lB%,f14Q CIXZ-~ and can be ra~ounted for as 223 -j932 interacting with pxl. It appears that Yaais overlapped for dilute solutions by 9,{cd) which is id&&led by the Raman line at 934 cm-l; for the solid aompound vaamay afford the abaorption at 945 cm-1 resolved from that of vi4 at 082 am-r. Whilst yap certaidy gives only one band at 802 urn-l for dilute solution, the position with regard to ygi)is less clear. A prominent band at 863 cm- 1 for the solid becomes markedly reduoed in intensity (at 866 cm-‘) in dilute solutions, where additional absorption is observed at 844 em-r. The components at 866, 844 cm-l appear similar to those at 865, 844 cm-l for 3,4-d~~tbylphenol (Sect. t-4). However, for the 2,5-isomer their ~~~~tatio~ as 237 + 567 (a”“) ~~ra~t~g with P= is preferred_ The three lowest EX’f~damen~ls are ~~~~ f&m the Raman western.

40

J. H. 8. GREEN,

D. J. HABEISOH

md W. KYBASTON

In the i.r. spectrum of the solid as,,is observed at 307 cm-l but for dilute solutions it is overlapped by the new strong, broad, absorption at 298 cm-1 due to y(OH). The remaining combination bands are theA’surn-levels-1688: 752 + 932; 1730: 802 + 932; 1870: 2 x 932. 1.6. 2,4-dimethylphenol Only one v(OH) or v(OD) absorption for unassociated molecules was observed (see Table 2). Bands for the liquid compound at 1351 and 1207 cm-1 decreased in intensity in the spectra of successively dilute solutions and there developed two strong, well-resolved bands at 1183, 1177 cm-l both of which were absent from the spectrum of the -0D phenol. They are ascribed to 6(OH) with which the sum 448 + 719 (A’) is ~~racting. Another rather prominent band at 1323 cm-l for solutions becomes a much weaker band at 1292 cm-l for the -0D compound; it clearly arises from Y* but this must, however, include a component of B (OH) motion. (In the spectrum of the -0D compound a prominent pair of bands at 952,906 is ascribed to 6 (OD) and y14,a coupling between these fundamentals accounting for their somewhat displaced positions.) Although ya8and yS3afford single absorptions-at 935 om-1 (resolved from that at 929 cm-l from yi4) and 876 cm-l, respectively-a well pronounced doublet at 816, 802 om-l is observed where yzais doubtless located, and it may well arise from two conformers, the existence of which has been inferred for o-alkylpheno~ [6]. However, the A” sum-level 320 + 487 ~teract~g with yz4could provide an alternative, though perhaps unlikely, explanation. The identification of the absorption at 301 cm-l, for dilute cyclohexane solution, as y (OH) is confirmed by its displacement to 225 cm-l for the -0D compound. The combination bands are accounted for as A’ sum-levels, several of which correspond to those for the other compounds in Table 4-1106 : 345 + 769; 1145 : 207 + 929; 1285: 570 + 719; 1748: 802 + 935; 1802: 876 + 935; 1850: 2 x 929; 1875: 2 x 935. 2. DICHLOROPHENOLS 2.1. 2,6-a~c~Zo~o~~~o~

In dilute solution this compound can adopt only the ~tramoleo~arly hydrogenbonded co~ormation, and only one pt(OH) or Y (OD) absorption, at 3527 or 2608 cm-l (in carbon disulphide solution) was observed for unassociated molecules. The i-r. spectrum was interpreted with reference to those of 2,6-dichlorotoluene and 2,6-dichlorofluorobenzene [l], and the fundamentals of all three molecules expressed in terms of Ce, symmetry are given in Table 5. A prominent doublet for dilute solutions at 1178, 1167 cm-i and the shift of this to 963 cm-l for the -0D compound establishes this as the predominately 8 (OH) vibration. However, there is no entirely satisfactory sum-level to account for the doublet by interaction with this fundamental: (215) + 955 (B,) involving r14 (aa) inferred at 215 cm-l (cf. Table 5) is numerically satisfactory but seems unlikely in view of the levels involved. The y (OH) vibration gives the very strong broad absorption at 400 cm-l for cyclohexane solutions, which is shifted to ~415 cm-f for bensene solution and is

Vibrational spectre of benzene derivatives-XV

41

Table 6. Wavenumbere (cm-l) of the fundamental vibrations of 2,klichlorophenol; dichlorotolueneand 2,tSdichlorofluorobenzene x, I, e*

Cl, OH, Cl 1.r.t

Cl, OD, Cl 1.r.t

3079 3055 1528 1462 1242 1102 1065 793 602 354 204

3072

895 (539) (215)

895

955 764 712 496 215 119

(953) 763 713 496

3079 1588 1450 1326 1275 1149 839 539 400 278

3072

3527 1178 400

2608 953 310

01 Vl V2 V6 V6

V6 V6

VI V8 V6 VlO Vll

4

~1s V16 V17 Vl(1 V18 %I

v (OH) 6 (OH) y (OH)

Cl, CH’, Cl 1.r.t

1210 1100 1064 778 599

_

-

3075 3063 1561 1470 1203 1089 1053 761 590 373 222

Cl, F, Cl 1.r.t

3072

3084

1566

1572 1462 1206 1112 1058 803 597 376 256

1209 1084 767 589 373

891 520

532

963 771 692 (500) 256 114

1287 1267 1149 832 522 400 270

R*$

259

3063 1586 1439 1269

1581 1269 (1203)

1154 805 493 401 256

1153 805 494 401 259

2,6-

894 (530) (215) 965 770 705 513 (260) (115) 3084 1583 1446 1255 (1205) 1154 829 539 401 279

* In l-X-2-Y.3-Z-benzene. t Dilute solution. $ Liquid.

there resolved from a sharp band at 400 cm-l assigned to yag(a”). This interpretation is confirmed by the persistence of sharp absorption at 400 cm-l and displacement of the broad absorption to 310 cm-l, in the spectrum of a c@ohexane solution of the -0D compound. The combination bands are-820 : 204 + 602 (A,) ; 1140 : (539) + 602 (B,) ; 1220: 2 x 602 (A,); 1276: 204 + 10% (A,), 496 + 764 (A,); five which are aocounted for by sum-levels corresponding exactly to those for 2,6-dichlorotoluene1654: 764 + 895 (EJ; 1712: 764 + 955 (A,); 1780: 2 x 895 (A,); 1841: 895 + 955 (B,); 1903: 2 x 955 (A,); and 3016: 1460 + 1682 (B,). 2.2. 2,5-dichlorophenol The expectation that this compound will exhibit rotational isomerism similar to that for o-chlorophenol is borne out by the observation (for dilute carbon disulphide

42

J. H. S. GREEN,D. J. FIABEISONand W. KYNASTON

solutions) of a prominent v (OH) absorption at 3530 cm-l arising from the intramolecularly bonded &-conformer, together with a. much weaker band at 3584 cm-l attributed to the trans-conformer. As found for o-chlorophenol [3], however, there are no other features in the infrared spectrum which can be unambiguously attributed to the trans-conformer. The 6 (OH) vibration affords a prominent band at 1189 cm-1 for dilute solutions in place of that at 1217 cm-l for the solid compound. Much weaker features at 1176 (shoulder) and 1167 cm-l for the solution (and 1170 cm-l for the solid) can rtrise from 458 + 707, 2 x 582, or 2 x 588. The shift of vs from 1345 cm-l (solid) to 1305 cm-l (solution) is normal; but that of bands at 1497, 1433 cm-l (solid) to 1480 cm-l and a doublet at 1449,1435 cm-l (solution) is unexpected. These features must arise from vs and v,, respectively, and the doublet attributed to the latter may arise from interaction of v, with a sum-level, possibly 1129 + vIs which is likely to be ~325 cm-l (cf. Table 6). The remaining details of interpretation follow from those for 2,5dichlorotoluene [2] with which comparison is made in Table 6. For example, v14 (Q’) and v,~ (a”) which are almost coincident for the latter molecule, give rise to the prominent bands at 907 and 860 cm-l, respectively, for the phenol. For dilute solutions, the prominent absorption at 398 cm-l can be reliably assigned to y (OH) and it is likely that the somewhat weaker band at 366 cm-l is also associated with this vibration. Similar absorptiona at 391, 361 and 333 cm-l have been thus assigned for o-chlorophenol [3]. There is a further, weaker band s,t 333 cm-l for 2,5-dichlorophenol but this could arise at least in part from vIB(a’). 458 +SSS; 1287: 588 + 707; The combination bands (all A’) are -1035: 1410: 2 x 707; and four others are accounted for in terms of y (CH) fundamentals -1714: 2 x 860; 1735: 797 +932; 1789: 860 +932; 1858: 2 x 932. 2.3. 3,4-&chlorophtmol The i.r. spectrum of this compound was investigated as a further example of a phenol with a meta-substituent and was interpreted with reference to the results for 3,4-dichlorofluorobenene [2] (see Table 6). Only one v (OH) vibration was observed for unassociated molecules in dilute solution: at 3606 cm-l (in carbon tetrachloride) or 3595 cm-l (in carbon disulphide.) The 6 (OH) vibration afforded a prominent doublet at 1180,117l cm-l which could arise either from two conformers, or from the interaction of sum-levels such as 486 + 683, or 275 + 903 with a single B (OH) fundamental. However, the y (CH) vibration vs3 and vz4were observed as well resolved doublets at 860, 824 end 810, 800 cm-l, respectively. Another prominent band at 903 cm-l is assigned to v14(a’) (cf. Table 6), and a weaker one at 885 cm-l to 2 x 445 or (209) + 683 interacting with v14. Weak bands were observed at 939, 927 cm-l, of which the latter is the stronger, in the region where vg2will occur and it is likely that they are two components of that fundamental; however, the A” sum 445 + 486 could be contributing to the spectrum in this region. The combination bands are accounted for by A’ sum-levels many of which

43

Vibrational spectra of benzene derivativee-XV

Table 6. Wwenumbera (cm-l) of the fundamental vibrations of %,6di&lorophenol, 2,6dichlorotoluene; 3,4dichlorophenol and 3,4-d x. Y, z* 0’

Cl,OH,

1.r.t:

3090

3086 3075 3062 1591 1664 1468 1390 1277 1264 120s 112s 1098 1052 877 702 673 626

v, V: % VI % VS 97

3072 3059 1598 1685 1480 1435 1305 1254 1239 1129 1084 1052 907 707 586 468 445 325 26S 219

v8 p9 %O 651 VI6 65, Vl6 Vl6 VI6 Vl7 v18 659 Go Vax

d

V9¶

%6 v96 V67 V98 V69 v80

v (OH) a (OH) y (OH)

Cl, CH,, Cl

Cl

1.r.t

{

260 221

932

942

860

871

797

809

699 582 445 305 219 (110)

693 643 439 309 200 110

3684 3530 1189 398 366 ( 333

W

1587 1564 1465 1274 1206 1097 1048 702 p 671 p 626 433 327 266

Cl, Cl, OH 1.r.t 3094 3075 3038 1601 1670 1472 1421 1281 1276 1234 1136 1128 1032 903 683 649 486 445 378 276 (200)

3100 3080 3030 1599 1681 1465 1396 1276 1267 1217 1146 1117 1036 902 688 642 484 444 376 274

939 927 860 1 842 810 t 800 690 681 445 330

940

t

309 203 119

Cl, Cl, F I.r.$

R.$ 3081 1597 1580 1470 1275 1257 1217 1117 1036 902 687 641 484 440 372 274 199

860 810 684 674 444 337 199 125

435 338 126

3606 1180 312

correspond exactly to those for 3,4di&.lorofluorobenzene [2J, as follows-835: 2 x 445; 966: 2 x 436; 1023: 373 + 649; 1137: 486 + 649; 1299: 2 + 649; 1652: 378 3-1276; 1678: 810 +860; 1718; 2 x 860; 1744: 810 + 939; 1809: 860 +939; 1852: 2 x 927; 1874: 2 x 939; 1924: 903 +1032; 3062: 1601 + 1472. Substantially complete assignments for nine disubstituted phenols have thus been made and the fundamentals associated with the -OH group, inclu~ the torsional mode identified for all of them. There is evidence for the existence of rotational isomers of the monomers for six compounds, but it is sometimes oonfused by the nobilities of sum-levels. The 8 (OH) band is sometimes a prominent

44

J. H. 8. GRIN,

D. J. ?&ULRISON and W.

KYNASTON

doublet, or has associated abaorptions. These features can always have explanations as sum-bands; the only unsatisfactory example is 2,6diohlorophenol where it is clear that only one conformer can occur. Splitting of one or more of the y (CH) absorptions is observed for the four oompounds possessing a substituent meta- to the -OH group; with the previous results [3] this has now been observed for a total of nine such phenols. For 2,5dichlorophenol, however, as for the o-halogenophenols [3], the intramolecularly bonded form dominates the spectrum and there is no unambiguous evidence for the trans-isomer apart from its v (OH) absorption.

The dimethylpheno~ were available as stands samples in the Division of Chemical Standards, N.P.L. and had purities (moles %): 2,3: 99.92; 24: 9W39; 25 : 9996; 2,6: 9989; 3,P: 9995; 3,5: 9996. The dichlorophenols were purified commercial materials of purity 98 per cent or better by gas chromatography. Deuterated phenols were prepared as described [3]. Infrared measurements were made using Unicam SP 100/130, Perkin-Elmer 226 and 301 spectrophotometers; solution spectra were obtained using the solvents carbon tetrachloride (3650-1300 cm-i), carbon disulphide (1400-400 cm-l) cyclehexane (500-50 cm-l) and benzene (500-50 cm-l). Raman spectra, excited with a Toronto arc, source were recorded photoelectrically using a Hilger E612 spectrograph. A~~l~~~~W~ thank Mr. P. I?. B. BAI~NAZZD and Mr. H. iS%.PAXSLZX for preliminary Raman and i.r. rn~u~rnen~, respectively, in the former National Chemical Laboratory.