Thermodynamic stability of carbonyl anions, R-.hivin.C:O. A molecular orbital examination

Chandrasekhar, Jayaraman; Andrade, Juan G.; Schleyer, Paul von Ragué

doi:10.1021/ja00408a075

Cited by 95 publications

(38 citation statements)

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“…The acetyl radical as well as the acetyl and benzoyl anions were the subject of theoretical calculations. 23,24 Interestingly, ∠CCO in the acetyl radical is ca. 130°whereas in acetyl and benzoyl anions it is ca.…”

Section: A Thermodynamic Datamentioning

confidence: 99%

Chemistry of Acyl Radicals

et al. 1999

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Section: A Thermodynamic Datamentioning

confidence: 99%

Chemistry of Acyl Radicals

et al. 1999

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“…Addition of diffuse functions to the HF/6-31G* basis does not significantly affect the optimized geometry, but significantly lowers the conformational energy. Since it is well-known that diffuse functions are necessary for a reliable description of an anionic group, 32,43,44 the HF/6-31+G* basis was used for all calculations of minimum energy conformers in the presence of a polar surrounding.…”

Section: Geometry Optimizations Of Pe and Pc Withmentioning

confidence: 99%

Effect of a Polar Environment on the Conformation of Phospholipid Head Groups Analyzed with the Onsager Continuum Solvation Model

1997

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The effect of the polarity of the environment on the conformation of the zwitterionic membrane lipid head groups phosphoethanolamine (PE) and phosphocholine (PC) has been investigated with calculations at the Hartree-Fock level using the 3-21G(*), 6-31G*, and 6-31+G* basis sets together with the Onsager continuum solvation model. Results suggest that in the gas phase both PE and PC adopt cyclic minimum energy conformations, in which an ammonium or N-methyl hydrogen closely approaches one of the nonesterified phosphate oxygens. In the case of PE, intramolecular interactions result in a proton transfer from the ammonium group to the phosphate oxygen, which however is suppressed by a moderate increase in the polarity of the surrounding medium. With increasing polarity of the environment, the cyclic structures of PE and PC still remain low-energy conformers but simultaneously for both head groups an almost identical extended conformer, typical of crystal structures, becomes increasingly favored. Already at ) 10, the extended conformer of PC is favored (-2.4 kcal/mol) relative to the cyclic one, while for PE the relative energy of the extended conformer approaches that of the cyclic one at ) 80. The similarity and increasing stability of the extended PE/PC conformers in the monomeric state and the fact that this conformer is also adopted in all crystal structures of PE/PC lipids, regardless of hydration and interaction pattern, indicate that the geometry of this conformer is determined by energetics intrinsic to the phosphoethanolammonium backbone. In lipid aggregates or a membrane environment the extended conformer becomes additionally stabilized by intermolecular ionic and hydrogen bond interactions with neighboring molecules substituting for the internal interaction that in the monomeric state constrains the zwitterionic dipole into a cyclic structure.

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“…Because many of the systems are anionic, diffuse functions are needed on all of the atoms. 3 Also, the basis set used on the central atom should include at least one set of d-polarization functions for the valence-p orbitals. In addition to modifying the shape of the valence orbitals, d functions allow probing of the controversial nature of bonding in hypervalent systems; that is, whether the three-center, four-electron bonding model 4 (where p orbitals on the central atom are primarily involved in the bonding) or the older expanded octet model 5 (where d orbitals on the central atom contribute substantially to the bonding) is more defensible.…”

Section: Introductionmentioning

confidence: 99%

Addition of Polarization and Diffuse Functions to the LANL2DZ Basis Set for P-Block Elements

et al. 2001

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Diffuse and polarization functions have been optimized for the LANL2DZ basis set for elements in groups 14-17. The optimized exponents are in most cases similar to those optimized with different effective core potentials, valence basis sets, or computational models. The average of the LANL2DZ results for different models is taken to be the best generalized set of exponents. The extended basis set gives good results (average deviation from experiment 0.11 eV) for atomic electron affinities with the B3LYP model, but is consistently low with the MP2 model. The extended basis set gives similar performance to the all-electron 6-31+G(d) basis set in calculations of vibrational frequencies and bond energies in selected main-group compounds, and is intermediate in speed between the 6-31+G(d) basis set and the unmodified LANL2DZ basis set. IntroductionTo support our experimental program on the energetics of hypervalent compounds, 1 we need to calculate structures, energetics, vibrational frequencies, and other properties for a number of species containing heavy main-group atoms, such as I 5 -, SbF 6 -, and BiCl 4 -. We have therefore become interested in expanding the range of available basis sets for heavy maingroup atoms.Basis sets used in calculations on these systems must meet certain criteria. 2 Computational efficiency generally dictates the use of effective core potentials (ECPs). Use of a relativistic core potential (RECP) can also largely account for the relativistic effects that become significant for heavier atoms. Because many of the systems are anionic, diffuse functions are needed on all of the atoms. 3 Also, the basis set used on the central atom should include at least one set of d-polarization functions for the valence-p orbitals. In addition to modifying the shape of the valence orbitals, d functions allow probing of the controversial nature of bonding in hypervalent systems; that is, whether the three-center, four-electron bonding model 4 (where p orbitals on the central atom are primarily involved in the bonding) or the older expanded octet model 5 (where d orbitals on the central atom contribute substantially to the bonding) is more defensible.Finally, the possible use of different basis sets on different atoms require basis set balance to avoid inaccuracies in the charge distribution in the molecule. "Balance" means that for each atom, the last functions of each symmetry added to the basis set contribute equally to energy lowering. 6-8 For example, adding diffuse functions to double-basis sets has a significant effect on the energy even for atoms. 9 Thus, using a small basis set for heavy atoms and a larger basis set for lighter atoms in the same molecule can lead to inaccurate electron distributions, energetics, and other properties. In practice, balance can be approached by using basis sets of a similar size for each atom.There is no comprehensive basis set for the main-group elements in general use that includes ECPs, diffuse functions,

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Thermodynamic stability of carbonyl anions, R-.hivin.C:O. A molecular orbital examination

Cited by 95 publications

References 0 publications

Chemistry of Acyl Radicals

Chemistry of Acyl Radicals

Effect of a Polar Environment on the Conformation of Phospholipid Head Groups Analyzed with the Onsager Continuum Solvation Model

Addition of Polarization and Diffuse Functions to the LANL2DZ Basis Set for P-Block Elements

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