Computational Study of the Thermochemistry of Organophosphorus(III) Compounds

Abstract

The enthalpies of formation of organophosphorus(III) compounds have been calculated at the G3X, G3X(MP2), and B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) levels of theory using the atomization energy procedure and the method of isodesmic reactions. The Delta f H298 degree values for 50 relatively large molecules with up to 10 non-hydrogen atoms, such as P(CH3)3, P(C2H5)3, P(OCH3)3, n-C4H9OPCl2, [(CH3)2N]2PCl, (C2H5)2NPCl2, and [(CH3)2N]2PCN, have been calculated directly from the G3X atomization energies. A good agreement between the known experimental values and G3X results for 14 compounds provides support to our predictions for remaining species whose experimental enthalpies of formation are unknown or known with relatively large uncertainties. On the basis of our calculations and sometimes conflicting experimental data a set of internally consistent enthalpies of formation has been recommended for organophosphorus(III) compounds. Our computational results call into question the experimental enthalpies of formation of P(C2H5)3 and P(n-C4H9)3. From comparison with most reliable experimental data, the accuracy of the theoretical enthalpies of formation is estimated as ranging from 5 to 10 kJ/mol. The recommended Delta f H298 degree values were used to derive the group additivity values (GAVs) for 45 groups involving the phosphorus(III) atom. These GAVs significantly extend the applicability of Benson's group additivity method and may be used to estimate the enthalpies of formation of larger organophosphorus(III) compounds, where high level quantum chemical calculations are impracticable.

A simple way to predict vibrational zero point energy of organophosphorus (III) compounds

“…These compounds can also be used as efficient coke-reducing additives within thermal cracking processes [4,5]. However, experimental thermochemical and kinetic data are either unavailable or available but with relatively large uncertainties [6,7]. To remedy this problem, the calculation of these quantities through current techniques of computational quantum chemistry or with empirical rules is needed.…”

Bond Dissociation Energies of Organophosphorus Compounds: an Assessment of Contemporary Ab Initio Procedures

“…The G3X method was found to reproduce wellestablished experimental results to an accuracy of ± 10 kJ mol −1 . 23 Large differences (up to 30 kJ mol −1 ) between experimental and computational data were reported for P(C 2 H 5 ) 3 and P(n-C 4 H 9 ) 3 , however, it was suggested that the experimental data should be remeasured. These authors performed a similar study for a set of 40 organophosphorus(V) compounds for which heats of formations were calculated using the G3X methodology and compared with available experimental data.…”

Revision of standard molar enthalpies of formation of glycine and l-alanine in the gaseous phase on the basis of theoretical calculations

“…For the 222 enthalpies of formation of small and moderate sized molecules with 2 to 10 non-hydrogen atoms, one of the latest version, Gaussian-3X (G3X) theory, achieves the so-called thermochemical accuracy of about 4 kJ Á mol À1 [2]. Recently we have assessed the capability of the G3X method for chlorinated and organophosphorus compounds with up to 12 non-hydrogen atoms [3,4]. It was shown that the G3X method is able to predict sufficiently accurate values of enthalpies of formation of these compounds and can be used for detecting anomalies in reported enthalpies of formation.…”