Long carbon–carbon bonds and beyond

Abstract

Advances in synthetic organic chemistry have facilitated the preparation and exploration of compounds exhibiting unusual bonding states. This review delves into carbon–carbon single bonds that are exceeding typical length of bonds, elucidating recent advances in understanding their bonding nature, properties, and chemical reactivity. Additionally, we examine factors contributing to the occurrence of such elongated bonds and their effects on other bonding parameters. Furthermore, we shift our focus toward the π-dimers of radical species, surpassing the limit of two-center two-electron (2c/2e) bonds, discussing their formation mechanisms, stability, and inherent properties. A key feature in the electronic structure of π-dimers is the bonding interaction of two unpaired electrons spanning multiple atoms, that is, multicenter two-electron (mc/2e) bonding. This review sheds light on the significant role played by extended carbon–carbon bonds (2c/2e bonds) and radical π-dimers (mc/2e bonding) in organic chemistry, providing valuable insight for future research on new functional materials.