Progressive systematic underestimation of reaction energies by the B3LYP model as the number of C-C bonds increases: Why organic chemists should use multiple DFT models for calculations involving polycarbon hydrocarbons

Density functional theory (DFT) energy studies of three types of hydrocarbon reactions involving C-C bond dissociation energies of alkanes based on the ethane template, the insertion of triplet methylene into C-C bonds to form higher alkanes and [2+2] cyclizations of substituted alkenes is described. It is recommended that energetic calculations should be performed that many DFT approaches and the results must be viewed as computational 'error bars' by analogy to experimental value determination.