The standard (p(o) = 0.1 MPa) molar enthalpies of formation in the condensed phase, Delta H-f(m)0, of 2,4-dichloro-5-methylpyrimidine, 2,4-dichloro-6-methylpyrimidine, 4,6-dichloro-2-methylpyrimidine and 4,6-dichloro-5-methylpyrimidine were derived from the standard molar energies of combustion, Delta U-c(m)0, in oxygen, to yield CO2 (g), N-2 (g) and HCl center dot 600H(2)O (l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization or sublimation, Delta H-g(cr, l)m(0), for these compounds, at T = 298.15 K were determined by high temperature Calvet microcalorimetry. Combining these values, the following enthalpies of formation in the gas phase, at T = 298.15 K, were then derived: 2,4-dichloro-5-methylpyrimidine, (79.6 +/- 4.1) kJ mol(-1), 2,4-dichloro-6-methylpyrimidine, (70.5 +/- 3.0) kJ mol(-1), 4,6-dichloro-2-methylpyrimidine, (68.7 +/- 3.3) kJ mol(-1), and 4,6-dichloro-5-methylpyrimidine, (78.1 +/- 2.5) kJ mol(-1). The gas-phase enthalpies of formation were also estimated by G3 theoretical calculations, which were extended to the computation of gas-phase enthalpies of formation of the other dichloromethylpyrimidine isomers, namely, 2,5-dichloro-4-methylpyrimidine, 4,5-dichloro-2-methylpyrimidine and 4,5-dichloro-6-methylpyrimidine, whose experimental study was not performed. (C) 2016 Elsevier Ltd. All rights reserved.