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Accurate Quantum-Chemical Prediction of Hydrogenation Enthalpies of Some Unsaturated Organic Compounds in the Gas Phase
  • ali khairbek,
  • Mohammad Abed Al-Hakim Badawi
ali khairbek
Tishreen University
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Mohammad Abed Al-Hakim Badawi
Tishreen University
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Abstract

The standard enthalpies of hydrogenation of 29 unsaturated hydrocarbon compounds were calculated in the gaseous state by the CCSD(T) theory of level with the 6-31g(d) and cc-pVXZ, where X =D, T, as well as by complete basis set limit extrapolation using two different formulas. Geometries of compounds were optimized at the M06-2X/6-31g(d) level. This M06-2X geometries were used in the CCSD(T) and extrapolation calculations with cc-pVXZ basis sets. Comparison of calculation and experimental results shows that the median absolute deviations (MAD) between the calculated and experimental enthalpies of hydrogenation range from 8.8 to 4.1 kJ mol-1 at CCSD(T) calculations , and for calculations, where using complete basis set limit extrapolation, the MAD have decreased to 1.5 kJ mol-1. The results of some calculations showed that the deviations from experimental values are located inside the “chemical accuracy” (±1 kcal mol-1 ≈ ±4.2 kJ mol-1 ). Very good linear correlations between experimental and calculated enthalpies of hydrogenation have been obtained at CCSD(T)/TZ method