High-Accuracy Extrapolated ab Initio Thermochemistry of the Propargyl Radical and the Singlet C3H2 Carbenes

Abstract

Total atomization energies and enthalpies of formation (0 and 298.15 K) are evaluated using the high-accuracy extrapolated ab initio thermochemistry (HEAT) scheme for the two stable singlet C(3)H(2) carbenes [cyclopropenylidene (c-C(3)H(2)) and propadienylidene (vinylidencarbene, l-C(3)H(2))], as well as for the 2-propynyl (propargyl, C(3)H(3)) radical. In the case of propargyl, the HEAT protocol predicts an enthalpy of formation of 354.9 +/- 1.0 kJ mol(-1) for 0 K; corresponding values of 498.1 +/- 1.0 and 555.6 +/- 1.0 kJ mol(-1) are estimated for c-C(3)H(2) and l-C(3)H(2). Additional consideration of temperature corrections leads to estimates of 352.2 +/- 1.0, 497.1 +/- 1.0, and 556.7 +/- 1.0 kJ mol(-1) for the heats of formation at 298.15 K of the propargyl radical, c-C(3)H(2), and l-C(3)H(2), respectively. Potential strategies for simplifying the HEAT protocol are also investigated and shown to have negligible impact on accuracy.