CHEMISTRY OF THE S=O BOND .13. STRUCTURES OF ISOMER-1(I) AND ISOMER-2(II) OF 4-METHYL-1,3,2-DIOXATHIANE 2-OXIDE AND 1,3,2-DIOXATHIEPANE 2-OXIDE(III) AT 256-K, 240-K AND 228-K

The structures of the two isomers of 4-methyl-1,3,2-dioxathiane 2-oxid e, C4H8SO3 (I, II), and 1,3,2-dioxathiepane 2-oxide, C4H8SO3 (III), ha ve been determined by X-ray diffraction methods for single crystals th at were grown in this case at low temperatures from the normally liqui d compounds. Compound (I): orthorhombic, P2(1)2(1)2(1), M(r) = 136.17, a = 7.204 (6), b = 13.670 (11), c = 6.041 (6) Angstrom, V = 595.91 An gstrom(3); Z = 4, D-x = 1.520 Mg m(-3), Mo K alpha (lambda = 0.71068 A ngstrom), mu = 4.49 cm(-1), F(000) = 288, T= 256 K, R = 0.042 for 778 unique reflections. Compound (II): orthorhombic, P2(1)2(1)2(1), M(r) = 136.17, a = 18.238 (6), b = 10.265 (3), c = 6.616 (2) Angstrom, V = 1 238.60 Angstrom(3), Z = 8, D-x = 1.460 Mg m(-3), Mo K alpha (lambda = 0.71068 Angstrom), mu = 4.31 cm(-1), F(000) = 576, T = 240 K, R = 0.03 2 for 1597 unique reflections. Compound (III): monoclinic, P2(1)/n, M( r) = 136.17, a = 6.060 (3), b = 11.185 (8), c = 9.186 (4) Angstrom, be ta = 101.32 (4)degrees, V = 610.52 Angstrom(3), Z = 4, D-x = 1.481 Mg m(-3), Mo K alpha (lambda = 0.71068 Angstrom), mu = 4.38 cm(-1), F(000 ) = 288, T = 228 K, R = 0.037 for 1161 unique reflections. Compound (I ) adopts a chair structure, which has a methyl group in an equatorial position and an axially oriented S=O group. Compound (II) is similar, except that the S=O group is equatorially oriented. Compound (III) ado pts a twist-chair conformation with a local approximate endocyclic two fold axis passing through S(1) and the middle of the opposite bond, C( 4)-C(5).