- 公益社団法人 有機合成化学協会
- 有機合成化学協会誌 (ISSN:00379980)
- vol.79, no.4, pp.290-299, 2021-04-01 (Released:2021-04-07)
The carbon-carbon covalent bond is one of the most basic concept in organic chemistry. Bond length, bond angle, and torsion angle among carbon atoms are nearly constant on the basis of the bond order and hybrid orbitals. On the other hand, highly strained hydrocarbons such as sterically-congested and/or curved polycyclic aromatic hydrocarbons have attracted much attention with regard to their characteristic features. Regarding the C-C single bond, whose standard length is 1.54 Å, several attempts have been made to elongate the C-C single bond to gain new insight into the chemical bond and understand what happens at the limits of a bond. In contrast to the standard C=C double bond with planarity, the overcrowded ethylenes (OCEs) with bulky substituents can adopt anti-folded, syn-folded and/or twisted forms due to the steric hindrance around the central C=C double bond, and thus many OCEs exhibit photo- and thermochromic behavior upon exposure to external stimuli. Herein, we focus on redox-active hydrocarbons with two dibenzocycloheptatriene units, where unprecedented flexible C-C bonds based on extremely elongated C-C single bonds and control of HOMO levels were demonstrated. Thus, these highly strained hydrocarbons could be promising candidates for the development of functional materials.