cisPro stabilization in prolyl carbamates influenced by tetrel bonding interactions.

NMR spectral and theoretical analyses of homologous prolyl carbamates reveal subtle charge transfer tetrel bonding interactions (TBIs), selectively stabilizing their cisPro rotamers. These TBIs involve C-terminal-amide to N-terminal carbamate carbonyl-carbonyl (n → π* type) followed by intra-carbamate (n → σ* type) charge transfer interactions exclusively in the cisPro motif. The number of TBIs and hence the cisPro stability increase with increasing number of Cβ groups at the carbamate alcohol. Increasing solvent polarities also increase the relative cisPro carbamate stabilities.