2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C–Hax⋯Yax cyclohexane contacts—results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures

Abstract

The complete 1H and 13C NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1–38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced 13C NMR chemical shifts (SCS) are discussed. C–Hax⋯Yax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C–Hax⋯Yax and 1,5-C–Hax⋯Yax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C–Hax and Yax groups along C–Hax⋯Yax contacts. The 1H NMR signal separation, Δδ(γ-CH2), reflects the strength of the H-bonded C–Hax⋯Yax contact.