Artículo de publicación ISIThe preferential conformations of a series of six–membered saturated heterocycles containing oxygen and sulfur atoms, 4-alkyl-6-methyl-1,3-dithiane, with alkyl=methyl, ethyl, propyl, isobuthyl, terbuthyl have been studied by means of ab-initio theoretical methods. The chair conformation is the most stable structure found for all compounds studied here, likewise in its counterparts: cyclohexane, dithiane, and dioxane. The structures show anomalous effects of the chemical shifts, in C2 and C5, due to as C-S → s* C-Hec hyperconjugative interaction. They are also affected by normal Perlin effect in C2, where C2-Hec coupling constants are larger than C2-Hax.