Chemistry of the S=O bond. 13. Structures of isomers 1 (I) and 2 (II) of 4-methyl-1,3,2-dioxathiane 2-oxide and 1,3,2-dioxathiepane 2-oxide (III) at 256, 240 and 228 K

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, P2₁2₁2₁, M_r = 136.17, a = 7.204 (6), b = 13.670 (11), c = 6.041 (6) Å, V = 594.91 ų, Z= 4, _Dx = 1.520 Mg m⁻³, Mo Kα (λ = 0.71068 Å), μ = 4.49 cm⁻¹, F(000) = 288, T = 256 K, R = 0.042 for 778 unique reflections. Compound (II): orthorhombic, P2₁2₁2₁, M_r = 136.17, a = 18.238 (6), b = 10.265 (3), c = 6.616 (2) Å, V = 1238.60 ų, Z= 8, D_x = 1.460 Mg m⁻³, Mo Kα (λ = 0.71068 Å), μ = 4.31 cm⁻¹, F(000) = 576, T = 240 K, R = 0.032 for 1597 unique reflections. Compound (III): monoclinic, P2₁/n, M_r = 136.17, a = 6.060 (3), b = 11.185 (8), c = 9.186 (4) Å, β = 101.32 (4)°, V = 610.52 ų, Z = 4, D_x = 1.481 Mg m⁻³, Mo Kα (λ = 0.71068 Å), μ = 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) adopts a twist-chair conformation with a local approximate endocyclic twofold axis passing through S(1) and the middle of the opposite bond, C(4)—C(5).

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