 These group contribution based equations are giving somewhat better results than the very simple equations based only on correlations with the molecular weight and the atom count.formula_1

formula_2

formula_3


formula_4

formula_5

formula_6

with

The group XCX is used to take the pairwise interaction of halogens connected to a single carbon into account.Its contribution has to be added once for two halogens but three times for three halogens (interactions between the halogens 1 and 2, 1 and 3, and 2 and 3).