research papers
Bond-length asymmetry in cyclopropane rings carrying σ-acceptor or σ-donor substituents has been studied using density-functional theory calculations and analysis of crystal structures in the Cambridge Structural Database. Both methods are in excellent agreement and show that σ-accepting halogen substituents induce positive asymmetry, but that this effect is reversed for σ-donors such as SiH3 or Si(CH3)3.