Thermochemistry of mono- and disubstituted acetylenes and polyynes at the Gaussian-4 level of theory

Gas phase enthalpies of formation at 298.15 K and 1 atm ( Δ f H ( g ) ∘ ) and adiabatic ionization energies (AIEs) were calculated at the Gaussian-4 (G4) level of theory for a suite of mono- and disubstituted acetylenes and polyynes. Δ f H ( g ) ∘ were estimated for 167 acetylene derivatives, of which only 16 had previously reported experimental values. Of the 122 acetylenes with G4 estimated AIEs, 30 compounds had available experimental characterization for comparison. Excellent agreement with thermochemical accuracy was obtained between G4 Δ f H ( g ) ∘ and AIEs and corresponding high quality experimental data and prior high-level theoretical estimates. The findings extend the existing thermochemical database on this important class of compounds to a range of derivatives without prior high level theoretical calculations or experimental reports.