Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part IV

Group contribution (GC) methods to predict thermochemical properties are eminently important process design. Following earlier work which presented a GC model in which, for the first time, chemical accuracy (1 kcal/mol or 4 kJ/mol) was accomplished, we here discuss classes of molecules traditional approach does not hold, i.e., many results beyond accuracy. We report new ring-strain-related parameters enable us evaluate heat formation alkyl-substituted cycloalkanes. In addition, definition appropriate group size is obtain reliable and accurate data systems electron density varies continuously but slowly between related species. For this case ring strain, G4 quantum calculations shown be able provide heats quantitative can use, absence experimental data, establish nearest-neighbour interaction extend range applicability method whilst retaining also found that strong van der Waals overlap highly congested branched alkanes qualitatively investigated by applying DFT calculations, an indication being inappropriate.