Feb., 1958
NOTES
255
case^.^^^ There are, however, cases where the solvent refractive index is not the dominating factor.s In such cases the observed effects have been attributed to solute-solvent interaction. l o Bayliss and McRae'l stated that the absorption frequencies of polar solutes are shifted to the red in solution if the dipole moment increases during the transition and they are shifted to the blue if the dipole moment decreases. I n the present investigation the absorption spectra of five sulfones and five ketones, the ketones being structural analogs of the sulfones, were determined in ethanol and in cyclohexane. The SOLVENT EFFECT ON THE ULTRAVIOLET data are given in Table I. ABSORPTION SPECTRA OF SULFONES AND TABLE I THE NATURE OF THE SULFUR-OXYGEN SOLVENT EFFECT O N THE ABSORPTION SPECTRA OF SULFONES BOND IN SULFONES (K-bands only are given. Wave lengths are in mp)
for these complexes is of interest in relation to that of the 18- ion. I n intensity, the ethyl iodidehalogen complexes compare well with the 290 mp peak of the triiodide absorption, rather than the relatively weak ethyl iodide absorption. On the other hand, there is no sign of the second peak in the 350-360 mp region which characterizes Is- and a number of other iodides. The fact that the ethyl iodide-bromine complex peak comes a t closely the same wave length suggests that the peaks represent a perturbed ethyl iodide absorption rather than a perturbed triiodide absorption.
Department of Chemistry, Annamalai Uniuersity, Annamalainagar, India Received November .4t 1067
Many investigations have been carried out to know the exact nature of the S-0 bond in sulfones and different conclusions have been arrived a t ; some believed that the bond is doubly covalent' and others thought that it is semi-polar.2 I n an attempt to find an answer t o this controversial problem we studied the solvent effect on the K-bands of several conjugated sulfones. Experimental Materials .-Methyl p-methoxyphenyl sulfone, m.p. 120120.5", was prepared by the method of Heppenstall an! smile^.^ Methyl p-methoxyphenyl ketone, b.p. 130-132 (15 mm.), was prepared from anisole and acetic anhydride by the Friedel-Crafts reaction. Benzalacetone was Eastman Kodak product purified by distillation before use (b .p. 144-146' (24 mm.)). Cinnamalacetone, m.p. 67.5-68", was prepared from freshly distilled cinnamaldehyde and acetone in the usual way. Benzalacetophenone, m.p. 56-57", was prepared before use. The following compounds were available in this Laboratory: methyl styryl sulfone,4 m.p. 79-80'; phenyl styryl sulfone,6 m.p. 74-74.5'; these were recrystallized before use. Ultraviolet Absorption Spectra.-The ultraviolet absorption spectra were determined with a Beckman quartz spectrophotometer, model DU. Ethanol used was 95% and it was purified by distillation after treatment with lead acetate and sodium hydroxide. Cyclohexaiie was purified by distillation after passing repeatedly through a column of silica gel.
Data and Discussion Solvent effects on the absorption spectra of organic compounds have been studied by many investigators. Sheppard6 stated that the refractive index is the dominating influence in all non-polar solvents. This view was confirmed in several (1) G. M. Phillips, J. 5. Hunter and L. E. Sutton, J . Cham. Soc., 146 (1945); D . Barnard, J. M. Fabian and H. P. Koch, ibid., 2442 (1949); E. D. Amstuta, I. M. Hunsberger and J. J. Chessick, J . A m . Chem. Soc., 7 3 , 1220 (1951); H.P. Koch and W. E. Moffitt, Trans. Faraday SOC.,47, 7 (1951). (2) S. Sugden, J. B. Reed and €1. Wilkins, J . Chem. S o c . , U T , 1525 (1925); A. I. Vogel, W. T. Cresswell, G . E. Jeffery and J. Leicester, ibid., 514 (1952); A. F. Wells, ibid., 55 (1949); C. C.Price and R. G. Gillis, J . A m . Chem. Soc., 76,4750 (1953). (3) M.E.Heppenstall and S. Smiles, J . Chem. Soc., 899 (1938). (4) M. Balasubramanian, V. Buliah and T. Rangarajan, ibid., 3296 (1955). (5) M.Balasubratnanian and V. Baliah, ibid.. 1844 (1954). (6) S. E. Sheppard, Reu. Modern Phys., 14, 303 (1942).
CeHia
CaHsOH
BYV. BALIAH AND SP. SHANMUGANATHAN C~HasozCHi p-CHsOCiHrSOzCHs CeHiSOzCeHr CeHbCH=CHSO2CHI CeHsCH=CHSOzCeHs C,HsCOCHa p-CHsOCeHdCOCH3 CaH6COCeH6 CBH~CH=CHCOCHI CeH&H=CHCOCeHs
Am..
Amfs
€mar
217 240 235
6,800 16,500 17,400
217 238 235
7,000 17,500 17,600
264
20,700
263
20,200
275 243 274 253
26,000 13,200 17,100 17,500
275 239 264 249
24,600 12,000 18,000 18,900
285
22,100
280
26,500
310
19,000
300
20,000
e m .
It is very significant to note that there is no change in the Amax of the K-band of methyl phenyl sulfone, diphenyl sulfone and phenyl styryl sulfone with change of solvent from ethanol to cyclohexane. Even in the case of methyl p-methoxyphenyl sulfone and methyl styryl sulfone the difference in A, is only 1 or 2 mp. These observations are in striking contrast with those made with the corresponding ketones for which the solvent effect is much more pronounced. We may, therefore, conclude that the difference in the energies of the ground and excited states in non-polar and polar solvents is about the same for sulfones, whereas this energy difference in polar solvents is less than that in non-polar solvents for ketones. This means that the stabilization of the excited state relative to the ground state is greater for ketones in ethanol. These facts can be explained on the basis of semipolar bond formulation for the s-0 bonds in sulfones. For example, methyl styryl sulfone would then be chiefly I in its ground state but derives a (7) G. M. Badger and R. S. Pierce, Speclrochim. Acta, 4 , 280 (1951);
N. D.Coggeshall and A. Pozefsky, J . Chem. Phye., 19, 980 (1951). 68, 1006 (8) N. 8. Bayliss and E. G. McRae, THISJOURNAL, (1954). (9) W. F. Maddams and R . Schnurmann, J . Chem. Phys., 17, 108 (1949); M. Kasha, Disc. Faraday Soc., 9, 14 (1950); H.McConnell, J . Chem. Phys., 20, 700 (1952); L. G. S. Brooker, G. H. Iceyes and D. W. Heseltine. J . A m . Chem. SOC.,7 3 , 5350 (1951). (10) N. S. Bayliss, J . Chem. Phya., 18, 292 (1950); E.F. G . Herington and W. Kynaston. J . Chem. SOC.,3143 (1952). 68, 1002 (11) N. 8. Bayliss and E. G. McRae, THISJOURNAL, (1954).
NOTES
256 0-
O C H = C H - - $ I $-CHI
bI /A-
