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

Abstract

Thermodynamic properties of phosphorus-containing compounds were investigated using high-level ab initio computations. An extended set of contemporary density functional theory (DFT) procedures was assessed for their ability to accurately predict bond dissociation energies of a set of phosphoranyl radicals. The results of meta-and double-hybrids as well as more recent methods, in particular M05, M05-2X, M06 and M06-2X, were compared with benchmark G3(MP2)-RAD values. Standard heats of formation, entropies and heat capacities of a set of ten organophosphorus compounds were determined and the low-cost BMK functional was found to provide results consistent with available experimental data. In addition, bond dissociation enthalpies (BDEs) were computed using the BMK, M05-2X and SCS-ROMP2 procedure. The three methods give the same stability trend. The BDEs of the phosphorus(III) molecules were found to be lower than their phosphorus(V) counterparts. Overall the following ordering is found: BDE(P-OPh) < BDE(P-CH 3 ) < BDE(P-Ph) < BDE(P-OCH 3 ).

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

“…An additional, yet equally challenging, goal is to elucidate the effect of stacking interactions between aromatic substituents on radical species and the polyaromatic coke surface, in an attempt to understand whether these interactions will accelerate or hinder the aforementioned competitive reactions. Relative stabilities, ease of formation, geometries, spin densities, and atomic charges of the nine phosphorus-containing radicals (Scheme 3) were reported; [39] the present study, however, focuses on the reactions between these radicals and the coke surface. Addition and hydrogen abstraction reactions were investigated (Scheme 4), initially on a benzene molecule as a small model representative of the carbonaceous layer and in a later step on a larger polyaromatic hydrocarbon (PAH), namely, ovalene.…”

“…The intrinsic reaction coordinate (IRC) [55,56] paths were traced to find the two associated minima directly connected to each transition state (TS) on the potential-energy surfaces. The BMK [57] functional, particularly developed for kinetics and well-known for its good performance in both radical and nucleophilic substitution reactions, [19,25,27,39,58] was employed in conjunction with the 6-311 + GA C H T U N G T R E N N U N G (3df,2p) basis set to further refine energies of B3LYP optimized structures. The BMK/6-311 + G-A C H T U N G T R E N N U N G (3df,2p)//B3LYP/6-31 + GA C H T U N G T R E N N U N G (d,p) level of theory was recently shown to effectively reproduce experimental heats of formation and thermochemical data in reactions of organophosphorus compounds and derived radicals.…”

“…The BMK/6-311 + G-A C H T U N G T R E N N U N G (3df,2p)//B3LYP/6-31 + GA C H T U N G T R E N N U N G (d,p) level of theory was recently shown to effectively reproduce experimental heats of formation and thermochemical data in reactions of organophosphorus compounds and derived radicals. [39] Electronic energies were corrected with the corresponding ZPVE scaled by a factor of 0.9806, and a scaling factor of 0.9989 was used for thermal corrections to the enthalpy. [59] Basis set superposition errors (BSSE) were estimated by use of the counterpoise method.…”

“…[30] In a separate study on the coke inhibiting effect of triphenylphosphine (TPPn), tri-o-tolylphosphine (TTP), and triphenylphosphine oxide (TPPO) (Scheme 2), TPPO was shown to be highly efficient. [31] In a recent study, Hemelsoet et al performed contemporary ab initio procedures to calculate bond dissociation energies of industrially relevant organophosphorus compounds, in an effort to identify the nature of the radicals formed and assess their ease of formation; [39] however, reactions between these potentially coke-inhibiting radicals and the coke surface have not yet been studied.…”

The Contribution of Molecular Modeling to the Knowledge of Pesticides

“…The recommended Δ f H°(298) values were used to derive the GAVs for 45 groups involving the phosphorus(III) atom and thus extending the applicability of Benson's group additivity method to estimate the Δ f H°(298) of larger organophosphorus(III) compounds (for which high level quantum chemical calculations could appear impracticable). Hemelsoet et al (2010) performed a comprehensive ab initio study on phosphoruscontaining species with three primary aims: a) to assess a broad variety of current computational methods to determine an appropriate level of theory for the calculation of reliable bond dissociation properties of phosphorous compounds; b) to provide thermochemical data such as the enthalpy of formation, the heat capacity and the entropy for a set of phosphorus-containing species representing industrially important cokeinhibiting additives; c) to compute bond dissociation enthalpies (BDEs) of these compounds to establish the stability of the formed radicals and their reactivity trends. Standard ab initio molecular orbital theory and density functional theory calculations were carried out using the Gaussian03/Rev.…”