Allingers force field in the last MM4 version calculate for hydrocarbons heats of formation with a rms error of 0.35 kcal/mol; vibrational spectra with a rms error of 24 cm-1 , rotational barriers with a rms error of 2.2 %, C-C bond lengths within 0.004 o and C-C-C angles within 1o ; later MM4 versions cover also compounds with heteroatoms , such as aliphatic amines