The title of this post summarises the contents of a new molecular database: www.molecularspace.org[cite]10.1021/jz200866s[/cite] and I picked up on it by following the post by Jan Jensen at www.compchemhighlights.org (a wonderful overlay journal that tracks recent interesting articles). The molecularspace project more formally is called “ The Harvard Clean Energy Project: Large-scale computational screening and design of organic

A simple correlation between a ring size and the hydrogen bonding as quantified by the O(Lp)/H-O σ* NBO interaction in that ring, indicated a 7- or 8-membered ring was preferred over smaller ones. Here is the same study, but this time using the π-electrons of an alkene as the electron donor. n  E(2), kcal/mol  O…H length, Å

One frequently has to confront the question: will a hydrogen bond form between a suitable donor (lone pair or π) and an acceptor? One of the factors to be taken into consideration for hydrogen bonds which are part of a cycle is the ring size. Here I explore one way of quantifying the effect for the series below, n=1-5 (4-8 membered rings). I will use the NBO approach.

Here I offer another spin-off from writing a lecture course on conformational analysis. This is the famous example of why 1,2-difluoroethane adopts a gauche rather than antiperiplanar conformation.