A study of the vinylidene-acetylene rearrangement using density functional theory

The vinylidene-acetylene rearrangement was investigated by density-functional theory, including pure and hybrid methods, with cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets. Several combinations of exchange and correlation functionals were used. All functionals yield geometries which compare well with the high-level ab initio results. Some combinations provide unphysical data. The BLYP, B3P86, B3PW91, B3LYP, and BHandH methods provide reasonable results. The BLYP method performs the best for this reaction providing geometry, harmonic frequencies and reaction energetics, a barrier of 1.53 kcal/mol and a reaction energy of −41.55 kcal/mol, in agreement with experimental data and high-level ab initio results.