Title: Conformational Analysis. 13C NMR studies of saturated heterocycles. substituent effects on the 13C chemical shifts of methyl-substituted -oxy- and 4-oxy-1,3-dioxolanes, 2-hydroxy-1,3,2-dioxaborolanes, 2-oxo-1,3-dioxanes, 2-hydroxy-1,3,2-dioxaborinanes and 2-oxo1,3,2-dioxathianes