Effects of CH–O and CH–π interactions on the conformational preference of a crownophane core unit†
Abstract
Relative energies of the rotamers of CH–CH2–X–R, X = O or CH2, R = CH3, C6H5 or o-CH3OC6H4) were calculated at the MP2/6-311G**//HF/6-311G** level as models of the crownophane core unit [1,1-bis(aryloxymethyl)ethylene]. The calculations show that CH–O and CH–π interactions play important roles in determining the conformational preference of the core unit. The terminal
C–C–O and C–C–O–C
bonds of the crownophane have an eclipse-trans conformation. Conformational analysis of model compounds shows that the eclipse-trans conformation is stabilized by a CH–O interaction. The
C–C–O and C–C–O–C bonds of this crownophane adopt a skew-gauche′ conformation that is stabilized by a CH–π interaction. Conformational analysis of model compounds shows that the C
C–C–O and C–C–O–C bonds of the core unit