CrossRef enabled

PAC Archives

Archive →

Pure Appl. Chem., 2006, Vol. 78, No. 4, pp. 791-811

Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

Chunhai Zou, Christine Lepetit, Yannick Coppel and Remi Chauvin

Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 Route de Narbonne, 31700, Toulouse Cédex 4, France

Abstract: The title journey is undertaken at the levels of both theory and experiment. Since 1983, homoaromaticity has been shown to play at most a minor role in the stability of Scott's [N]pericyclyne hydrocarbons - the first ring carbo-mers of cycloalkanes. This statement has been systematically refined for N = 3-6 by using both classical theoretical tools and newly designed tools based on electron localization function (ELF) analysis. The compatibility of the [5]- and [6]-pericyclyne cores with vertex functionalities was established by the synthesis of 20 oxy (carbo-cyclitol) derivatives. The stereoisomeric resolution of two of them has been achieved. Hexaoxy-[6]pericyclynes are actually potential precursors of the carbo-benzenes. Criteria based on density functional theory (DFT) calculations (magnetic, energetic, structural/"electronic") show that the aromaticity of carbo-[N]annulenic species is comparable to that of their parent molecule. This has been challenged by the synthesis of several novel carbo-benzenic molecules with various substitution patterns. The theory-experiment interplay is pursued by considering ring carbo-mers of other conjugated ring systems such as radialenes. The second carbo-mers (butadiyndiyl-expanded rings) of [3]radialene and benzene are also envisioned. Hexaphenyl-carbo2-benzene has been observed by 1H and UV-vis spectroscopy.