Selecting weak bonding sites: effect of a methyl group in the acetylene–polyyne interaction

There are two distinct types of attractive sites for weak bonding of acetylene to a polyyne. Ab initio calculations carried out for these sites for several acetylene–polyyne dimers show that methylation noticeably changes their energetic ordering. This selection of one site over another on the basis of a functional group substitution can be understood, in part, from features of the electrostatic interactions.