Blue‐ and Red‐Shifting C−H⋯O Hydrogen Bonds of Cyclic Ethers with Haloforms: Effect of Ring‐Size and Consistency with Bent's Rule

Abstract

AbstractA DFT‐based computational study is carried out to delve into the interplay between hyperconjugation and rehybridization effects underlying the formation of blue‐ or red‐shifting H‐bonds (HBs) in 1 : 1 complexes of cyclic ethers (HB acceptor) of varying ring‐size with haloforms, CHF3 and CHCl3 (HB donor). The calculations reveal that with decreasing angular strain (increasing ring‐size) of the cyclic ethers, the extent of blue‐shift increases for 1 : 1 complexes with CHF3, while a reverse sequence is observed with CHCl3, eventually leading to a red‐shifting HB in the oxepane : CHCl3 complex. It is noted that the trend in the shift of C−H stretching fundamental is not mirrored by the C−H bond length or interaction energies for both the systems studied, that is, the low sensitivity of the changes on the strain on the O‐atom of HB acceptor (cyclic ethers) is to be emphasized.