C-13 NUCLEAR MAGNETIC-RESONANCE SPECTRA .10. SUBSTITUENT EFFECTS ON THE C-13 CHEMICAL-SHIFTS OF ADAMANTANES, DIAMANTANES, AND TRIAMANTANES

The 13C n.m.r. data of a variety of substituted adamantanes, diamantenes, 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.