Carey, FA; Smith, PM; Maher, RJ; Bryan, RF
Single-crystal x-ray structure analyses have been carried out for trans-2-phenyl-l,3-dithiane 1-oxide (5), cis-2-phenyl-l,3-dithiane 1-oxide (6), and 2-phenyl-l, 3-dithiane trans- l, trans-3-dioxide (7) to examine the effects of oxygen substitution on the geometry of the 1, 3-dithiane ring. For 5, a = 12.206 (2), b = 5.749 (1), c = 14.809 (2) Å. β = 97.11 (1)°; for 6, a = 5.007 (1), b = 20.134 (4), c = 10.095 (3) Å, β = 98.76 (3)°; and for 7, a = 12.315 (3). b = 5.851 (1), c = 14.829 (3) Å, β = 98.44 (2)°. The space group is P21/c in each case with Z = 4. The dithiane rings have a chair conformation somewhat more puckered than that of cyclohexane with endocyclic torsion angles in the range 5873°. The endocyclic C(2) valence angle shows a marked variation from compound to compound, being 109.6° in 5, 112.9° in 6, 114.2° in 7, as compared to 114.9° in 2-phenyl-l,3-dithiane (4) itself. An argument accounting for the steric dependence of this angular variation is offered in terms of transannular dipolar interactions between the two sulfur atoms and oxygen and is discussed in relation to conformational equilibria in solution. Short C-H…O contacts indicative of significant dipolar interactions are found in all three crystal structures. 1977, American Chemical Society. All rights reserved.