The conformational enthalpies (DeltaH) of 2-methyl-(-1.76 kcal mol(-1)) and 4-methyl-1,3-dithiane (-1.75 kcal mol(-1)) were obtained by the analysis of C-13 chemical shifts as a function of temperature. These energies are in excellent agreement both with calculated values (B3LYP/6-31G(d,p)) and with literature values based on 2,4-dialkyl-1,3-dithiane. The results confirm the similarity between the conformational energies of the methyl group at the 2 and 4 positions of the dithiane ring and that of methylcyclohexane, despite the larger distances between ring 1,3-syn-axial hydrogens and the closest methyl axial hydrogen in the dithiane ring. The possibility of a buttressing effect on the 2,4-dialkyl-1,3-dithianes previously studied and the rationale of 1,3-syn-axial steric interaction are discussed. (C) 2003 Elsevier B.V. All rights reserved.657416998592