13C nuclear magnetic resonance spectra. Part 10. Substituent effects on the 13C chemical shifts of adamantanes, diamantanes, and triamantanes
Abstract
The 13C n.m.r. data of a variety of substituted adamantanes, diamantanes, and triamantanes are presented. The α-substituted chemical shifts (SCS) can be described by gauche XC interactions, the magnitudes of which decrease in the sequence BrC > HC > OC ≳ CC. Similarly, gauche interactions of the types HX and CX contribute to the β-SCS, but additionally the β-SCS are increased, if the β-carbon atoms possess antiperplanar γ′-carbon atoms. Steric interaction of the substituent with gauche γ-carbon atoms seem to cause rather downfield rather than upfield shifts of the γ-signals. The hyperconjugative interaction of parallel Cα–Cβ- and Cβ′–Cα′-bond orbitals increase the γanii-SCS of the hydroxy and, to a smaller extent, the bromine substituent.
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