Chemistry of the S=O Bond. 13. Structures of Isomers 1 (I) and 2 (II) of 4-Methyl-l,3,2-dioxathiane 2-Oxide and 1,3,2-Dioxathiepane 2-Oxide (III) at 256, 240 and 228 K

摘要

The structures of the two isomers of 4-methyl-1,3,2-dioxathiane 2-oxide, C4H8SO3 (I, II), and 1,3,2-dioxathiepane 2-oxide, C4H8SO3 (III), have been determined by X-ray diffraction methods for single crystals that were grown in this case at low temperatures from the normally liquid compounds. Compound (I): orthorhombic, P222U Mr = 136.17, a = 7.204 (6), b = 13.670 (11), c = 6.041 (6) A, V = 594.91 A3, Z = 4, D, = 1.520 Mg nr3, Mo Ka (A = 0.71068 A), fi = 4.49 cnr1, F(0OO) = 288, T = 256 K, R = 0.042 for 778 unique reflections. Compound (II): orthorhombic, FI{12, Mr= 136.17, a = 18.238(6), b = 10.265(3), c = 6.616 (2) A, V = 1238.60 A3, Z= 8, Dx = 1.460 Mg m~3, Mo Ka (A = 0.71068 A), fi = 4.31 cm"1, F(000) = 576, T = 240 K, R = 0.032 for 1597 unique reflections. Compound (HI): monoclinic, P2], Mr = 136.17, a = 6.060(3), b = 11.185(8), c = 9.186 (4) A, /3 = 101.32(4)°, V= 610.52 A3, Z= 4, Dx = 1.481 MgnT3, Mo Ka (A = 0.71068 A), x = 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 (HI) adopts a twist-chair conformation with a local approximate endocyclic twofold axis passing through S(l) and the middle of the opposite bond, C(4)-C(5).