The crystal structures of 2,2-dimethyl-5-nitroso-1,3-dioxan-5-yl benzoate, C(13)H(15)NO(5), (I), 2,2-dimethyl-5-nitroso-1,3-dioxan-5-yl 4-chlorobenzoate, C(13)H(14)ClNO(5), (II), and 5-nitroso-1,3-dioxan-5-yl 4-chlorobenzoate, C(11)H(11)NO(5), (III), have been determined in order to gain insight into the conformational preference of alpha-benzoyloxynitroso. Unfavourable 1,3-diaxial interactions force (I) and (II) to crystallize in the 2,5 twist-boat conformation, whereas compound (III), lacking this destabilizing interaction, crystallizes in the chair conformation.