Conformational analysis in multisulfur heterocycles. VIII. 3,3:6,6-Bis(tetramethylene)-s-tetrathiane and 3,3:6,6-bis(pentamethylene)-s-tetrathiane. Slow s-tetrathiane chair-to-twist, chair-to-chair, and twist-to-twist interconversions. X-ray crystallographic studies

Examination of the /sup 1/H dnmr spectra of 3,3:6,6-bis(tetramethylene-2,2,3,3-d/sub 4/)-s-tetrathiane provided activation parameters for the s-tetrathiane twist to chair (..delta..H* = 14.7 +- 0.5 kcal/mol, ..delta..S* = -3 +- 2 eu, ..delta..G* = 15.7 +- 0.1 kcal/mol at 26.2/sup 0/) and chair to twist (..delta..H* = 15.7 +- 0.5 kcal/mol, ..delta..S* = -2 +- 2 eu, ..delta..G* = 16.2 +- 0.1 kcal/mol at 26.2/sup 0/) processes as well as clear evidence for an unusually high potential barrier to s-tetrathiane twist-to-twist interconversion (..delta..H* greater than or equal to 16 kcal/mol). The /sup 1/H dnmr spectrum of 3,3:6,6-bis(pentamethylene-2,2,3,3,4,4-d/sub 6/)-s-tetrathiane revealed changes consistent with slow s-tetrathiane chair-to-twist and twist-to-twist stereomutation as well as slow cyclohexane ring reversal. The dnmr data also provide accurate measurement of the chair:twist ratio in a number of s-tetrathianes. An X-ray crystallographic study of 3,3:6,6-bis(pentamethylene)-s-tetrathiane showed it to be triclinic, space group P1 Vector, a = 6.632 (6), b = 8.462 (6), c = 6.446 (6) A; ..gamma.. = 93.92 (6)/sup 0/, BETA = 103.23 (6)/sup 0/, ..gamma.. = 96.90 (6)/sup 0/; Z = 1; d/sub x/ = 1.396 g cm -/sup 3/; R = 0.025 for 2715 Nonzero reflections measured with a scintillation counter. In this crystal, the molecule is centric with all three rings in chair conformations. Average bond distances are S-S = 2.035 (2), C-S = 1.842 (2), and C-C = 1.525 (1) A.