4-Substituted ([Formula: see text] and CH 2 F)-6-Me-1,3-dioxanes together with model derivatives (cis- and trans-4-CH n F 3−n -6-t. Bu-1,3-dioxane, and 2-Me-4,6-disubstituted 1,3-dioxanes) were prepared and their p.m.r. spectra analyzed, using i.a. INDOR techniques. Special features which correlate configuration and p.m.r. data are discussed and especially the fluorine–hydrogen (long-range) couplings have been studied. From vicinal (ring) coupling data (using appropriate models), from the vicinal exo-couplings 3 J(H4,CF 3−n H n ) and from absolute shift values, the equilibria were obtained in the conformational heterogenous trans-4-CH n F 3−n -6-Me-1,3-dioxanes (n = 0 → 2). The results, according to the different methods, are mutually in excellent agreement, as is also the case for ΔG 0 (CF 3 ), obtained approximately from dipole moment measurements. The anomeric effect is pronounced, and the conformer with the axial fluoromethylated substituent is the preferred one (CF 3 :76%; CF 2 H:62%) at room temperature in CS 2 . For CH 2 F the contrary seems to be the case (presumably for entropy reasons also). Finally ΔH 0 (chair–twist) was evaluated at 3.7 kcal/mol [Formula: see text] using 2 J(H2) criteria in trans-4-CF 3 -6-t. Bu-1,3-dioxane.
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Dirinck et al. (1972) studied this question.
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