The heats of alcoholysis in isopropyl alcohol of the d0 Ti or Zr compounds MR4(R = Me3SiCH2, Me3CCH2, or PhCH2), M(NR′2)4(R′= Me or Et), and MCl4(and some Hf analogues) have been measured, as well as the heats of solution in Pr1OH of M(OPri)4, RH, R′2NH, or HCl; from these and subsidiary data standard heats of formation and thermochemical mean bond energy terms have been derived [M–X in kcal mol–1: Ti–Cneopentyl,44; Ti–C,63; Ti–N, 81; Ti–O, 115; Zr–Cneopentyl, 54; Zr–C, 74; Zr–N, 90; Zr–O, 132; Hf–Cneopentyl, 58; Hf–N, 95; Hf–O, 137].