The effects of the first- and second-row substituents on the structures and energies of PH4X phosphoranes. An ab initio study

Abstract

Pentacoordinated phosphoranes, PH4X, substituted with a full range of firstand second-row groups have been studied with ab initio computations. The apically and equatorially substituted trigonal-bipyramidal (TB) and apically substituted square-pyramidal (SP) conformations were fully optimized with the 3-21G(*) and 6-31G* basis sets. Frequency calculations were performed at 6-31G* on the optimized structures. Correlation corrections through the MP4 level were carried out on these 6-31G* structures. Energies calculated with zero-point energy corrections, i.e., at MP4SDTQ/6-31G* + ZPE, provide relative energies of various isomers. The apically substituted SP structures for PH4X (X = Li, Na, BeH, and MgH) are the most stable. The intrinsic apicophilicities of the firstand second-row groups are derived and are compared to available experimental data. The apicophilicities (in kcal mol"1) are OH (0.4) > SH (-0.1) > CH3 (-0.9) > PH2 (-3.3) > NH2 (-7.2) > SiH3 (-8.6). Due to their high degree of ion pair character, PH4F and PH4C1 are unsuitable as models for relative energy comparisons, interaction energies were evaluated by calculating various PH4X (X = NH2, PH2, OH, SH) conformations. Natural bond orbital (NBO) analysis on these conformers shows that the interaction is due chiefly to nx -_ .. Inductive and bonding contributions are estimated for the first-row group substituents. The effects of substitution (e.g., relative energies) that are dominated by inductive interactions correlate linearly with group electronegativities. meinschaft, Fonds der Chemischen Industrie, and the Convex Computer Corporation. Y. Zhang was supported by an Alexander von Humboldt Foundation fellowship. We thank H. Xie for technical assistance.

Ab initio calculations on P?C bond cleavage in phosphoranyl radicals: implications for the biodegradation of organophosphonate derivatives

“…51,55 Four TBP minima all exhibiting equatorial localization of the unpaired electron are also found, and these minima differ either by the axial/equatorial substitution pattern of the ligands-1a has the methyl group equatorial whereas 1c, 1d and 1e place it axial-or as hydroxyl group rotamers amongst the latter three. The hydrogen bonding and hyperconjugative interactions that control the hydroxyl group orientations have been extensively discussed for other hydroxy-substituted phosphoranyl radicals, 48,51,52,55 and we find similar results here; in particular, the greater apicophilicity of hydroxyl compared with methyl 66 is offset by favorable hyperconjugative interactions between two equatorial hydroxyl groups, making the energies of the lowest energy conformers, 1a and 1c, very similar at all levels of theory. Relative energies for all five structures as calculated at different levels of theory are given in Table 1.…”

Single and double ionization of the camphor molecule excited around the C 1s edge

“…The final geometries were obtained with DFT using the Becke's three parameter hybrid functional with the LYP correlation functional . The final structures were submitted to analysis of Natural Bond Order (NBO) with the density functional B3LYP using the basis set 6‐311+G** . This computational procedure has been employed previously on similar systems with success .…”

Synthesis, structure, and reaction of tricoordinate stibine and tetracoordinate stiboranide

“…The relative preference of substituent occupying the apical site is particularly known as apicophilicity [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. From many experimental systems and theoretical calculations, an oxygen atom is determined to be much more apicophilic than a carbon atom [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Antiapicophilic compound, which violates relative apicophilicity of the elements, generally has high energy and is unstable, thus easily isomerizes into its stable apicophilic compound.…”