226
Chapter 17 Some Tetrahedral Molecules
Table 17-1: Bond-lengths (Å) for some sulphones.
r(SX)
r(SY)
r(SO)
(a)
1.530
1.530
1.397
(b)
1.530
1.530
1.405
(c)
1.55
1.985
1.408 (ass.)
(d)
2.011
2.011
1.404
(e)
1.763
2.046
1.424
(f)
1.759
1.561
1.410
(g)
1.777
1.777
1.431
REFERENCES: (a) Hagen, K., Cross, V.R. and Hedberg, K., J. Mol. Struct., 44, 187 (1978). (b)
Lide, D.R., Mann, D.E. and Fristrom, R.M., J. Chem. Phys., 26, 784 (1957). (c) Hargittae, I.,
Lecture Notes in Chemistry 6, Sulphone Molecular Structures, Springer Verlag, Berlin, 1978;
C.W. Holt and M.C.L. Gerry, Chem. Phys. Letts. 9, 621 (1971). (d) Hargittae, I., Acta Chim.,
Acad. Sci. Hung., 60, 231 (1969). (e) Hargittae, M., and Hargittae, I., J. Chem. Phys., 59, 2513
(1973). (f) Hargittae, I., and Hargittae, J. Mol. Struct., 15, 399 (1973). (g) S. Saito and F.
Makino, Bull, Chem. Soc. Jap., 45, 92 (1972).
S-F, S-Cl and S-C single bonds, and the S-O bond-lengths are shorter than the
1.48 Å for the double bond of free SO. With respect to the S-O bond-lengths, each
of the structures (35) and (36) alone predicts double-bond character. However, the
bond-lengths reported in Table 17-1 suggest that the expanded valence-shell
structures account better for the S-X and S-Y bond-lengths than do the “increasedvalence” structures with no valence shell expansion. As is the case for 3
F SN , the
sulphur atom carries a formal charge of +2 in the Lewis octet structure (34). Presumably, expanded valence-shell structures of type (5) should be similarly
preferred to structures of type (6) for
2
4
SO
 , whose S-O bond lengths of 1.48 Å
13
are much shorter than the single-bond length of 1.70 Å. It should be noted however, that for structure (5), some further “increased-valence” may be developed by