The spectra and structure of sulphur-containing organic compounds—IV. The vibrational spectra and conformations of haloidmethylmethylsulphones CH3SO2CH2X

Spectrochimico ACIY. Vol. Printed ,n Great Bntam

058468539/87 $3.00 + 0.00 ~0 1987 Pergamon Journals Ltd

43A. No 3, pp 309-315. 1987

The spectra and structure of sulphur-containing organic compounds-IV. The vibrational spectra and conformations haloidmethylmethylsulphones CH3S02CH2X*

of

A. B. REMIZOV,~$ F. S. BILALOV~ and I. S. POMINOV§ tKazan

Institute

of Chemistry and Technology, 68 K. Marx Street, Kazan 420015, U.S.S.R. and §Kazan State University, 18 Lenin Street, Kazan 420008, U.S.S.R. (Received 7 April 1986; accepted 22 May 1986)

Abstract-The i.r. and Raman spectra of CH3S02CH,Br (II) in their liquid, solution mixture of frans and gauche conformations spectra has been investigated and the value of polarized i.r. spectra of crystalline I and II has

the and has AH

haloidmethylmethylsulphones CHjS02CH2CI (I) and crystalline states have been recorded. The presence of a been established. The temperature dependence of the i.r. = H(gauche) - H(trans) found. The band dichroism of the

been considered. The frequencies of the torsion vibrations have been found and the value of the internal rotation barrier measured. The interpretation of vibrational spectra is given and a normal coordinate analysis has been carried out.

EXPERIMENTAL

INTRODIJrXION Data on internal rotation about the S-C bond in acyclic sulphoxides have been obtained earlier Cl]. The relative stability of tram and gauche conformations is determined by the balance of various intramolecular interactions. To evaluate the contribution of these interactions to the total internal energy rotation one must obtain data on the conformations of molecules which differ only in the coordination of the sulphur atom and in the nature of the substituents of the S and C atoms. It is intriguing to compare the characteristics of internal rotation about the S-C bond in sulphoxides and in compounds of the RS02CH2X type. In Ref. [2] the vibrational spectra and conformations of the methanesulphonilchlorides ClS02CH2X (X = CH3, Cl, Br) were studied. It was shown that a mixture of trans and gauche conformations was present in the liquid and solutions, with AH = 0 + 200 cal/mol. Later the Raman spectra of a number of crystalline methanesulphonilchlorides were investigated [3]. The molecular structure of bromomethylsulphone CH$02CH2Br in the gas phase was investigated by the electron diffraction method [S]. Unfortunately, the authors assumed a priori that the molecules were in one conformation. Under this assumption all the molecules in the gas phase appeared to have the gauche conformation. A new analysis may be necessary, assuming the possibility of a mixture of conformations. The present paper reports an investigation of the vibrational spectra and conformations of chloromethylmethylsulphone CH3S02CH2Cl (I) and bromomethylmethylsulphone CH3S02CH2Br (II).

Infrared spectra in the range 40&4000 cm- ’ were obtained on a Karl Zeiss UR-20 spectrometer. Raman spectra were obtained using a DFS-24 spectrometer equipped with a He-Ne laser. The experiment proceeded as in Refs [l] and [2]. Sulphones I and II were synthesized by literature methods [S]. Their spectra are presented in Figs l-4. RESULTS AND DISCUSSION The study of dimethylsulphone by the electron diffraction method has shown that the molecules have a conformation in which the C-H bonds (CH3 group) and the bonds at the S atom (S=O and S-C) are in the gauche orientation [6]. Therefore, it can be assumed that in the case of sulphones I and II two nonequivalent conformations are possible: with the tram and gnu&e orientations of the S-X and S-C bonds. The determination of the number of conformations in liquids and solutions is possible by comparison of the spectra of the liquids and crystals. In most cases molecules in the crystalline form exhibit only one

b

200

*Part III: A. B. REMIZOV, F. S. BILALOV and I. S. POMINOV, J. m&c. Strucr. 96, 1 (1982). SAuthor to whom correspondence should be addressed. 309

300

Frequency

Fig. 1. Raman

spectra

(cm

of sulphone

I

I

400

500

‘)

I (a, liquid; b, crystal).

A. B. REMEOVet

310

2

a

‘I

s

C

al.

conformation. If there is a mixture of several conformations in the liquid state and in solution, then a reduction in the number of conformations occurs on crystallization which results in the freaing out of bands and lines in the i.r. and Raman spectra. One conformation of sulphones I and II in the skeletal vibration range (less than 6OOcm-i) has six fundamental vibrations, excluding two torsional vibrations which yield very weak bands and lines in the spectra. However, in the Raman spectrum of liquid sulphone I seven medium and strong lines are observed, which should be classed as fundamental vibrations. There are eight such lines in the Raman spectrum of liquid sulphone II (Table 1, Figs 1 and 2). Hence, liquid sulphone spectra cannot be interpreted on the basis of one conformation. The crystallization of sulphone I is accompanied by the freezing out of the 490 cm- ’ band in the i:r. spectrum and of the 492 cm-’ line in the Raman spectrum. In the case of sulphone II the 488 cm-’ band and the 251,486 and 771 cm-’ lines are frozen out. These data testify to the presence of a conformational equilibrium in liquid sulphones 1 and II. Only one conformation remains in the crystal and therefore sulphone crystallization is accompanied

LLJd!Jl

50

100

250

300

350

450

Frequency (cm-‘)

Fig. 2. Raman spectra of sulphone II (a, liquid; b, crystal).

Fig. 3. Polarized i.r. spectra of crystalline sulphone I; solid and broken lines represent spectra in the two interperpemdicular polarizations of ix. radiation.

Fig. 4. Polarized i.r. spectra of crystalline sulphone II; solid and broken lines represent spectra in the two interperpemdicular polarizations of i.r. radiation.

Vibrational

spectra

and conformations

Table 1. Observed CH,S02CH,CI Raman* Infrared* Liquid Crystal Liquid Crystal

452s 465~ 490m 507s

453m 467~ 512m

680m

682m

756s

770m

790m 882s 95ow

790w 885m 951w 968~ 981m

977s 1124s 1160s 125Om 1320s 1395m 1420~ 2938m 2956m 3022s

1128m 1162m 1254m 1288~ 1329s 1356~ 1390m 1408m 1425~ 1470w 2935m 2950m 3015s 303ow

119w 187m

132~ 187m

294~ 309vs

294~ 312~s

374s 456m

389s 451m

492m 509s

507m

frequencies

of CH,S0,CH2X

311

and assignments

CH,S0,CH2Br Infrared Raman Liquid Liquid Crystal Crystal 1lOw 161m 251m 280s 300m

451s 476sh

452s 475sh

361m 454m 461vw 486m 506m

Assignments

121w 154m

sCHzX fiscx

273s 292m 313vw 367m 445m 464vw 499m

/?csc PSOZ 154x2 tso, wsoz 300+ 187 (161) BSG

502m 544w 561~ 654s 687~ 710m

657s 687~ 711m

654~s 709s

651~s 695sh 703m

764s

768s

764m 771m

760m -

v,csc

855s 951w

856s 951w

850~

858~

KHz PCH,

975s

968m

971m

PC&

1105s 1149s 1215m

977s 1065~~ 1106s 1150s 1218m

1102m 1140m 1206~

1092s 1135m 1207~

tCHz v,SOz wCHz

1318~

1314s

1314s

1304w

1289m

1398w

1386m 1416m

1380s 1406m 1422m 1471sh 2932m 2942m 3014s

1382m 1409w

1376m 1400w 1411w 1431m 2935m >

v,SOz 6CH3 GCHZ 6CH, 6CH3

679~s 702~ 760m

679~s 697~ 762m

790m 885~ 994w

791m 892~

970w

982~ 1033w 1115s 1159w 1242~ 1296~

1123s 1151m

2934s 2959m 3025~ 3034w

2938s 2952m 3016m 3018m

7

280 x 2 280 + 300 vCBr v,csc

VCCl

2934m 2958m 303ow

3074sh

1065vw

2952m 3019w \ 3028m 3037vw 1

*vs., very strong; s, strong; m, medium; w, weak; VW, very weak; sh, shoulder, tv, stretching; p, bending; 6, deformation; p, rocking; w, wagging; t, twisting;

by the freezing out of bands and lines in the spectra. Table 1 presents the interpretation of the spectra of sulphones I and II. The assignment of the vibrations of the C-S02-CH3 group has been carried out by analogy with similar vibrations of dimethylsulphone [7] and ClS02CH3 [2]. The classification of the vibrations of the CHZCl and CH2Br groups has been carried out on the basis of the ClS02CH2X spectra

PI. The C-S02-C fragment has five fundamental deformational vibrations in which the valency angles at the S atom vary. They can be described as C-SSC bending, SO2 bending, SO, wagging, SOZ rocking and SO2 twisting. These vibrations are close to corresponding dimethylsulphone vibrations. Judging by the CIS02CH2X spectra [2], the vibration SCX bending lies below the above-mentioned vibrations of the C-W-C fragment. Hence, the 187 cm- ’ line may be

vCH

r, torsion.

assigned to SCCI bending and the 161 cm- ’ line to SCBr bending. There are weak 119 and 110 cm-’ lines in the Raman spectra of liquid sulphones I and II. Since all the deformational vibrations have already been pointed out, these lines may be assigned to the torsional vibrations of the CHzX group. This is confirmed by the increase in the frequencies of these vibrations on crystallization, which is normally observed in the case of torsional vibrations. As has been shown by the normal coordinate analysis of the sulphoxides CH3S(0)CH2X [ 11, mixing of the valent vibrations C-S and C-X occurs. Hence, we shall initially carry out tentative assignment of v (C-X) and v(C-S) vibrations, making it more precise by normal coordinate analysis. The i.r. 760 and 701 cm-r bands of crystalline dimethylsulphone are due to C-S-C antisymmetric and symmetric stretching modes. Similar vibrations are also observed in sul-

A. B. REMIZOV et al.

312

phone spectra: at 756 and 680 cm- ’ (sulphone I), 764 and 710 cm- ’ (sulphone II). The v(C-Br) vibration normally lies below v(C-S) and the 654cm-’ band (sulphone II) is assigned to it. The v(C-Cl) vibration lies above v(C-S) and the 790 cm-’ band may be assigned to it. The CHJ group has five deformational vibrations, to which 974,978,1325, 1414 and 1414 cm-’ bands are due in the ClS02CHJ spectrum, in the i.r. spectrum of crystalline dimethylsulphone CHJ rock bands at 936, 981,995 and 1005 cm- ‘; CH3 symmetric deformation bands at 1313 and 1335 cm-‘; CHs asymmetric deformation bands at 1407 and 1430 cm-‘. In keeping with these data deformation vibrations of the CHJ in sulphone I and II are given (Table 1). The CH2 has four deformation vibrations with which bands at 873 (rocking), 1152 (twisting), 1248 (wagging) and 1394 cm-’ (scissoring) are associated in the i.r. spectrum of ClS02CH2Cl. Similar bands are also present in the spectra of sulphones I and II. The assignment of the valent C-H vibrations of sulphones I and II presents no difficulties. To obtain a more complete interpretation of the sulphone I and II spectra, a normal coordinate analysis of the sulphone I vibrational spectra of the trans and gauche conformations has been carried out by the

method described in [8]. The internal coordinates are given in Fig. 5. The torsional vibrations of the CH3 and CHXl groups havebeen left out ofconsideration. The lengths of the bonds and the valent angles of the C-SO& fragment were taken as in dimethylsulphone [9]: R(S=O) = 1.445 A, R(C-S) = 1.778 A, [(CSC) = 103”, L(OS0) = 117.9”, L(CS0) = 108.8”. The geometric parameters of the methyl and CH2Cl groups were as follows: r(C-H) = 1.08 A, r(C-Cl) = 1.77 A, all the angles being tetrahedral. A valent force field was used [S]. The calculations were made in terms of natural coordinates, the force constants of the truns and gauche conformations were assumed to be equal. The force constants of acyclic sulphoxides [l] and haloid hydrocarbons were taken as the initial valent force field. The kinematic coefficients were calculated automatically by the algorithm suggested in [S]. The initial force constants were varied to improve agreement between the observed and calculated vibration frequencies. The final set of force constants is presented in Table 2. Table 3 gives the observed and calculated frequencies and the potential energy distributions in which terms less than 15 are omitted. The results of the normal coordinate analysis are in good agreement with the empirical vibrational assignments listed in Table 1. It should only be noted that the

Table 2. The force field of CHsSOsCHsCl* Value Force constant

Value

106cm-*

t

Ar,

a.34

AR, AR,

5.5

14.6 5.0 8.34

5.35 3.53 9.36 3.21 5.35

0.65 0.88 2.0 1.72 2.0 0.78 0.6 0.9 2.0

0.5 0.67 1.53 1.31 1.53 0.6 0.46 0.69 1.53

0.05 0.05 0.3 0.1 0.15

0.03 0.03 0.19 0.06 0.1

0.35 0.35 0.4 0.45 0.47

0.24 0.24 0.27 0.31 0.32

Force constant

lo6 crne2

t

0.70 0.5 0.6 0.70 0.65

0.48 0.35 0.42 0.48 0.45

- 0.035 - 0.035 -0.035 0.12 - 0.02 0.15 0.12 - 0.02 0.43 0.15 -0.015 - 0.035 -0.015 - 0.035

- 0.026 - 0.026 - 0.026 0.09 -0.016 0.11 0.09 - 0.016 0.3 0.11 -0.011 - 0.026 -0.011 - 0.026

&stretch)

AR;o AG

K(beN :;: AYI A& AYE A/94 Aa A09

AYZ H(stretch-stretch) Ar,, Arr Ar,, A% A%, AR5 ARs, AR6 ARsr ARIO A(stretch-bend)

Arl, Aar Arl, AS2 A&, AYI

*The names are taken from [S]. tForce constant units are mdyn.A-’ rndyn.A. rad-’ (bend).

ARs, Ayr AR,, A/I4 AR6, Ays ARp,, Ayr ARio, AtIp &end-bend) Aq, Aas bar, AjIB1 A/%, ABs AI&, AYI A/Jr, A& AYI, Ah

Av, , Av, AY1,M4 A&, A& A&, AYE A/94.ABs AS,, Aa A&, AfIr0 A/34,A89

(stretch), mdyn.rad-’

(stretcbbend)

and

Vibrational

Fig. 5. Internal

coordinates for the sulphone 1.

1420 1408 1390 1356 1320 1250 1160 1124 980 950 880 790 756 680 507 490 452 374 309 294 187

and conformations

tram conformation

Table 3. Observed

Observed

spectra

and calculated

of

498 446 405 312 295 187

3030 3025 3025 2968 2943 1426 1410 1360 1320 1280 1245 1148 1090 992 964 845 800 738 676 511

frequencies

-

(cm- ‘) for CH3S02CH2CI

PED*

(trans)

ArdlW, ArdlW Ar1(lW, Ar,(lW Ar,(lW, Ar2(50),ArAW

ArdlW, ArdlW Ar,(lOO), Ar,(l@% Ar,(lOO) Aa,(lW, Aa,(lOO), Aa4(lW Aal(lOt$ A%(lW AMlWr A&(100), A/%(100), ABi (loo), AMl’Wr AMlOO), AMlO’% A&(1@% A&(100),

431 390 330 300 199

* 100FkkLiz/Fkk L:),,,. Values less than 15 have been omitted

313

valent C-S and C-Cl vibrations become mixed. The calculated frequencies of /ISO vibrations differ in the case of trans and gauche conformations, pS02 gauche being greater than BSOl trans. This relationship of the calculated frequencies remains unchanged when the force constants are varied. Therefore, the 490 cm- ’ band can be assigned to the tram and the 507 cm ’ band to the gauche conformation. During crystallization the trans conformation band is frozen out. Hence, in a crystal sulphone I is the gauche conformation. Thus the normal coordinate analysis made it possible to assign the bands observed to certain conformations. It is significant that relative rather than absolute values were used in this process. The conformations of sulphones I and II in the crystalline state can be determined from the relative dichroism of the absorption bands of polarized i.r. spectra. The technique is similar to that of Ref. [lo]. Let us consider a molecule consisting of two parts which rotate about each other, as a result of which several rotational isomers (conformations) appear. The crystal has only one of these. Let there be vibrations vi and v2 in the i.r. spectrum of the molecule in question, the former assigned to some combination of internal coordinates of one part of the molecule, the latter to the other. The intensitv of the absorntion band

Calculated Tram Gauche 3030 3025 3025 2968 2943 1426 1410 1360 1320 1296 1230 1158 1090 992 964 860 811 730 707

of CHjSO~CH2X

Aaz(lOO) Aa,(48), Aa,WJ Aa0W, A82(88), M(80), A8,(75), Aa3CW AR,(1W, A84(15), A85(15), A&(15), A&0(15) Ak(l’W, AWlOO), A&0(100) A&(100) A/&(100), A&(100), A6io(lOO) A8,(60), A8,(60), Aa (15) A/53(100), Am AMlOO), A&(100), A@,o(lOO) AR,,(lOO), Ak(40) AR,,(34) Ay2(47), AR,,(25), Ayl(l5)

314

A. B. REMIZOV et al.

of the ith molecular vibration is proportional to &i/aQi (j is the dipole molecular moment, Qi is the normal coordinate of a given vibration) and to cos2y, where y is the angle between the vectors aji/aQ and E (E is the electric vector of the lightwave). The absorption bands v1 and v2 are characterized by the vectors @lag, and aji/aQ2, whose direction can be found from vibrational assignments obtained from normal coordinate analysis [S]. In the polarized i.r. spectra of the crystal the ith band intensity Z (vi)reaches a maximal value I,, (vi) when the polarizer is turned through a certain angle a_(vi). Z(vi) obviously falls to its minimum Zmin(vi) when the polarizer is turned through an angle amin a,,(vi) f90”. Each of the bands v1 and v2 is c=haracterized by its angles a,,(vI) and amx(v2) [or amin and ati(v2)]. The relationship between a&v,) and a,, (v2) determines the relative dichroism of the bands v1 and v2 in polarized i.r. spectra. The mutual orientation of the vectors aji/aQt and aji/aQ, is different for different conformations, since when part of molecule rotates about the other, the vectors aji/aQ, and aji/aQ2 also turn. Hence, different conformations have different relative dichroisms of the bands v1 and v2. Let us take, for example, two rotational isomers, in one of which aji/aQ, and @/i3Q2 are parallel and in the other perpendicular. When a,,,,(~~) =a _(v2) _+90” = amin in polarized i.r. spectra, it can be concluded that the molecules in a crystal have a conformation with perpendicular aji/aQ, and aji/aQ2, since a_(vl) = a,, (v2) should be expected for a conformation with parallel aji/aQ1 and aji/aQz. It should be noted that such an analysis of molecular crystal spectra is possible only within the framework of the “oriented” gas model. As has been pointed out, the possible conformations of sulphones I and II are truns and gauche, which differ in the mutual orientation of the CH,SO, and CH,X groups. To determine sulphone conformation in the crystal, let us analyse the relative band dichroism of the symmetric stretching vibrations of SO, (1162 cm- ’ for sulphone I; 1150 cm - ’ for sulphone II) and symmetric and asymmetric stretching vibrations of CH, (2950 and 3015 cm-* for sulphone I; 2942 and 3014 cm-’ for sulphone II). Judging by the contours and dichroism, these bands may be considered in terms of the oriented gas model. For the bands of the stretching vibrations v(S02&, and v(CH2),, the vector aji/aQ is directed along the bisector of the angle O=S=O or H-C-H, and for the bands of the stretching vibrations this vector is perpendicular to the bisector ~V32)asym and lies in the plane H-C-H. In the polarized i.r. sulphones I and II of crystalline spectra a,(v(S02),,) = amin(v(CH,),) = a,(v(CH2),,) are observed (Figs 3,4). In the trans conformation the vectors aji/aQ of the bands v(SO,),,,,, and v(CH,),, are parallel and the corresponding bands should have the same dichroism, i.e. a_(v(S02&,,,) = a_(v(CH,),,,). Since the opposite dichroism of the bands under consideration is observed, it can be concluded that in the crystalline state the molecules of sulphones I and II

have no truns conformation. Hence, the conformation of sulphones I and II is gauche. It is noteworthy that this holds true irrespective of the number of molecules in the elementary cell of a crystal or of a crystal’s orientation. After establishing the conformation of the molecules in a crystal one may assign the bands to particular conformations. The new bands and lines appearing in liquid and solution spectra are assigned to the truns conformation. Such an assignment is similar to the one made above on the basis of normal coordinate analysis. The study of the effect of medium polarity on the relative intensities of bands and lines combined with the knowledge of the relative polarity of conformations makes it possible to assign bands to definite conformations. The content of the more polar conformation increases with the growth of medium polarity (see e.g. [l I]). The following pairs (doublets) of close bands belonging to different conformations have been chosen in sulphone spectra: 484-502 cm-’ (I) and 490-507cm-’ (II). In solution spectra the relative intensity of the first component of these doublets increases with the polarity of the medium (solutions in CCL+,benzene, dioxane and acetonitrile). According to Ref. [ 121 it can be assumed that the dipole moment of the tram conformation of sulphones I and II is larger than that of the gauche conformation. For this reason the bands at 484 cm-’ (sulphone I) and 490 cm-’ (sulphone II) can be assigned to the tram conformation. This also agrees with the results of normal coordinate analysis. To determine the values AH = H(guuche) - H(truns) the dependence of the optical densities D of tram and gauche conformation bands on temperature has been investigated. This approach is well known (see e.g. [ll]). The i.r. spectra of sulphone I and II solutions in acetonitrile have been obtained at different temperatures over the range 25 to -45°C. D values of the 484 and 502cm-’ bands (sulphone I) and of the bands at 490 and 507 cm-’ (sulphone II) assigned to truns and gauche conformations have The linear dependences been measured. In [0(484 cm-‘)/&502 cm-l)] =Al/T) arid In [0(490 cm-‘)/D(507 cm-‘)] =fll/T) have been obtained. The angles of inclination a of these lines have been found Then the values of m have been calculated from the relationship tga = AH/R. For sulphone I AH = H(guuche) - H(truns) = 0.67 +0.25 kJ/mol and for sulphone II AH = 1.17 + 0.25 kJ/mol. The errors resulting from the treatment of the above dependences by the least squares method have been noted. The content C of the gauche conformation in CH,CN solution has been estimated by the formula C/(1 -C) = Cg(guuche)/g(truns)] exp (-AH/RT), where g are the statistical conformation weights, g@uuche) = 2 and g(truns) = 1. This approach gives adequate results [ll]. It has been established that the gauche and tram conformations in the solution of sulphone I in acetonitrile are in the ratio 0.6:0.4 and in sulphone II solution in the ratio

Vibrational

spectra

and conformations

0.55:0.45. The content of the gauche conformation in solutions in dioxane (C’) has been estimated by comparing the values A = D(vglluche)/d(vtrans) in the i.r. spectra of solutions in acetonitrile (A) and dioxane (A’): C’ = A’C;[A(l -C)+A’C]-C” = 0.7 has been obtained for sulphone I and C’ = 0.6 for sulphone II. It has been assumed that the polarity of the medium does not influence the relationship of the molar extinction coefficients of the bands at 484502 cm-’ and 49@507 cm-‘, since, in keeping with normal coorinate analysis, these vibrations of trans and gauche conformations are of the same type (they have identical distributions of potential energy). In the Raman spectra of liquid 1 and II we have identified the frequencies of torsional vibrations v, (Table 1). This permits one to evaluate the internal rotation barrier. The spinning of heavy tops occurs in the molecules of I and II; hence, vr may be regarded in the harmonic oscillator approximation: vf=

V*F; V* = V,+4Vz+9v,+

where Vi values determine the potential energy of internal rotation V = 1/2ZVi(l -cos ice) [ll]. F = h/8dcl,,d, I,,,,is the reduced inertia moment. Since only one line v, is observed, it can be assumed that v,(tmns) = v,(gauche). Ire,, for trans conformations of I and II has been calculated as in [13] using the parameters chosen previously while in normal coordinate analysis. F = 0.76 cm-’ (I)and0.61 cm-’ (II), v* = 18580cm-’ (I) and 19 840 cm-’ (II) were obtained. In molecules of types I and II the potential energy of internal rotation is normally fairly well described by two or three terms Vi [It], and for their determination the knowledge of just one value of V~is insufficient. However, interesting evaluations of Vi may be carried out. Compounds I and II may be described as ethane-like molecules, for which the minima of internal rotation energy occur at rotation through an angle of 120”. For such molecules V is mainly determined by V, adding the much smaller V, and V,. If V is mainly determined by V,, i.e. V = (VJ2) (1 - cos 3a), then from v* we get V, = 24.7 (I) and 23.3 kJ/mol (II). If the energy is determined by two terms of the series, i.e. V = (VJ2) (1 -cosc() +(VJ2) (1 -cos3a) or V= (V,/2) (1 -cos2c() + (V,,‘2) (1 -cos 3a), then to derive Vi, alongside with v, the difference of the energies of the trnns and gauche

315

of CHJS02CH2X

conformations AE = AH = 314 V, or 314 Vz may be considered [ 111. We have calculated that for solutions in non-polar solvent, AE z 0. Hence, V, or V2 are close to zero, the value of V, being close to the one derived above. To summarize, data on internal rotation about the S-C bond in the sulphones CH,SO,CH,X have been obtained: the type of conformations occurring established the values of AH and determined conformation content, and the values of internal rotation barriers have been estimated. The analysis of the data on the conformations of ClSO,CH,X [2] has shown that in RSO,CH,X molecules the position of the conformational equilibrium remains virtually unshifted

on transition

from

R = Cl to R = CH,.

The

in the CH,X group does not affect the position of the conformational equilibrium either. It is difficult to distinguish the kind of intramolecular interactions that would largely determine molecular conformations. type of halogen

Acknowledgements-The authors are grateful to BUTENKO for the synthesis of sulphones I and III.

G.

G.

REFERENCES [t] [2] [3] [4] [5]

[6] [7] [S]

[9] [lo] [I l] [I21 [13]

A. B. REMIZOV, F. S. BILALOV and I. S. POMINOV, J. molec. Struct. 96, 1 (1982). A. B. REMIZOV and 0. A. SAMARINA, Zh. Prikl. Spectrosk. 22, 870 (1975). R. AROCA, J. ALI and E. A. ROBINSON, J. molec. Struct. 116, 1 (1984). V. A. NAUMOV and R. N. ZIATDINOVA, Zh. Struct. Khim. 24, 48 (1983). G. G. BUTENKO, A. N. VERESHCHAGIN and L. S. LIAKISHEVA, Izv. Akad. Nauk. SSSR, Ser. Khim. 1559 (1981). I. HARGITTAI, Lecture Notes of Chemistry. Vol. 6. Springer, Berlin (1978). T. UNO, K. MACHADA and K. HANAI, Spectrochim. Acta 27A, 107 (1971). M. V. VOL’KENSHTEIN, L. A. GRIBOV, M. A. EL‘YASHEVICHand B. I. STEPANOV, Kolebanija Molekul (Molecular Vibrations), 2nd Edn. Nauka, Moscow (1972). D. E. SANDS, Z. Kristallogr. 119, 245 (1963). A. B. REMIZOV, Opt. Spectrosc. 39, 204 (1975). W. J. ORVILLE-THOMAS (ed.), Internal Rotation in Molecules. Wiley (1974). 0. EXNER and I. B. N. ENGBERT, Co/[. Czech. Chem. Commun. 44, 3378 (1979). L. N. MARGOLIN, Yu. A. PENTIN and V. I. TYULIN, Opt. Spectrosc. 35, 824 (1973).