Cyclic and linear structures of C-13: A computational study

Recently, a linear structure of C-13 was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C-13 are thu s presented. The computations are performed at ab initio level using the st andard 6-31G* basis set. Electron correlation is treated by density functio nal theory (Becke3LYP) and perturbation treatment (MP2=FC). With the densit y-functional approach the standard 6-311G* and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C-2v symmetry) is located about 90 kJ/mol below the linear form (D-infinity h symmetry), whi le a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form r epresents less than 10% of the equilibrium isomeric mixture. Computed IR sp ectra are also reported. The stability evaluation corresponds to the findin gs of ion chromatography.