An ab initio Molecular Orbital Study of Bonding in Fluorocarbonium Ions

1971 ◽  
Vol 49 (22) ◽  
pp. 3708-3713 ◽  
Author(s):  
N. C. Baird ◽  
R. K. Datta
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Minimal Basis ◽  
Fluorine Substitution ◽  
Abstraction Reaction ◽  
Carbonium Ions ◽  
Hydride Abstraction ◽  
Resonance Stabilization

Ab initio molecular orbital calculations are reported for the series of carbonium ions (CH3)+, (FCH2)+, and (F2CH)+ and for their neutral molecule counterparts CH4, CH3F, and CH2F2. The energies and wavefunctions for the carbonium ions have been calculated both with and without including the carbon 2pπ orbital in the minimal basis set in order to unravel the inductive destabilization and resonance stabilization due to fluorine substitution. The increase in bonding energy with multiple fluorine substitution is less than linear, due primarily to nonadditivity in the dative carbon–fluorine π bonding. The "saturation" effect noted previously for the hydride abstraction reaction enthalpies is shown to be due primarily to stability effects in the neutral molecules themselves rather than to energetic effects of the carbonium ions.

Structures of simple anions from ab initio molecular orbital calculations

1976 ◽  
Vol 29 (8) ◽  
pp. 1635 ◽  
Author(s):  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Limited Information ◽  
Orbital Theory ◽  
Comparable Quality ◽  
Split Valence ◽  
Theoretical Results

Ab initio molecular orbital theory with the minimal STO-3G and split-valence 4-31G basis sets is used to obtain geometries of 18 anions:OH-, NH2-, HF2-, BH4-, BF4-, C22-, CN-, NCN2-, N3-, NO2-, NO3-, 0CCO2-, CO32-, HCOO-, CH3COO-, C2O42-, C4O42- and C(CN)3-. The theoretical results are compared with experimental results from the literature. The STO-3G basis set performs somewhat worse for anions than for neutral molecules. On the other hand, the 4-31G basis set gives good results and predicts bond lengths to within 0.02� for all the molecules considered. Limited information on bond angle predictions suggests that these are of comparable quality to those for neutral molecules. The tricyanomethanide ion is predicted to be planar.

Molecular Orbital Calculations of Cu-Halides

1981 ◽  
Vol 36 (10) ◽  
pp. 1095-1099 ◽  
Author(s):  
H. Itoh
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Energy Levels ◽  
Basis Set ◽  
Orbital Energy ◽  
Ionic Character ◽  
Molecular Orbital Calculations ◽  
Ab Initio Hf ◽  
Mo Theory

An ab initio HF MO theory is applied to CuX, CuX2 (X = F and Cl) and (CuCl)3 . Although the detailed sequence of energy levels depends upon the basis set used, high-lying orbital energy levels have largely halogen p-like character, whereas low-lying orbital energy levels have largely Cu 3 d-like character. This is in agreement with the chemical intuition of a highly ionic character of these compounds.

1H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole

1989 ◽  
Vol 67 (6) ◽  
pp. 1027-1031 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Substituent Effects ◽  
Spin Coupling ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Minimal Basis ◽  
Parent Molecule ◽  
Nuclear Magnetic

The proximate spin–spin coupling constant between the methyl protons and the ring protons, 5J(H,OCH3), is extracted from a full analysis of the 1H and 19F nuclear magnetic resonance spectra of 3-fluoroanisole in CS2 and acetone-d6 solutions. The values of 5J(H,OCH3) imply that the less polar cis conformer is slightly more stable at 300 K than the more polar trans conformer in both solvents, in agreement with geometry-optimized STO-3G MO computations for the free molecule. The latter also find a higher barrier to internal rotation of the methoxy group for 3-fluoroanisole than for the parent molecule. The present results are compared with other measurements of the conformer ratio for the vapor and for solutions. The STO-3G and 6-31G structures of the cis and trans conformers are compared. The C—F bond length is computed more reliably with the minimal basis set, as is the COC bond angle. The internal angles of the benzene moiety are, of course, found more accurately with the 6-31G basis. The computations indicate additivity of the substituent effects on the internal angle, as found experimentally for a variety of benzene derivatives. Keywords: 1H NMR of fluoroanisole, conformations of fluoroanisole, molecular orbital calculations for fluoroanisole.

Halogen...O(Nitro) Supramolecular Synthon in Crystal Engineering: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

1997 ◽  
Vol 53 (6) ◽  
pp. 1006-1016 ◽  
Author(s):  
F. H. Allen ◽  
J. P. M. Lommerse ◽  
V. J. Hoy ◽  
J. A. K. Howard ◽  
G. R. Desiraju
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Crystal Engineering ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Model Dimer ◽  
Experimental Crystal ◽  
Van Der Waals Radii ◽  
Experimental Crystal Structure ◽  
Intermolecular Perturbation Theory

Crystallographic data for 309 C—X...O(nitro)—C, X = Cl, Br, I, interactions, involving 245 symmetry-independent X atoms, have been investigated out to 0.2 Å above van der Waals radii limits [\nu(O) + \nu(X)]. A total of 138 (45%) of these interactions are shorter than \nu(O) + \nu(X), with the degree of interpenetration of the X and O atoms increasing in the order Cl < Br < I. The analysis also shows that: (a) the C—X...O angle tends to linearity as the X...O distance shortens, (b) the angle of approach of X to the C—NO2 plane is preferentially less than 45° for Cl, with an increasing tendency to in-plane X approach in the order Cl < Br < I, and (c) the halogen (X) forms either (i) mono-coordinate interactions with one nitro O atom, with X...O in a cis relationship to the nitro C substituent about the N—O bond, or (ii) approaches both nitro O atoms in a bifurcated manner; the tendency to form such bifurcated motifs increases in the order Cl < Br < I. Only iodine consistently forms short interactions with both nitro O atoms. Ab-initio-based molecular orbital calculations, using intermolecular perturbation theory (IMPT) applied to a nitromethane–1-chloro-2-methylacetylene model dimer, agree with the analysis of experimental crystal structure geometries. The IMPT calculations yield an attractive interaction energy of ca −6 kJ mol−1 for Cl...O at the 6-31G* basis set level. Calculations for Br...O at the (only available) [6s4p1d] basis set level indicate that this interaction is more attractive than Cl...O.

An Ab Initio Molecular Orbital Study of Sulfur-Substituted Carbanions: Toward an Understanding of Regiochemistry in the Chlorination of Unsymmetrical Sulfides

1997 ◽  
Vol 50 (6) ◽  
pp. 517 ◽  
Author(s):  
Jack Leon Ginsburg ◽  
Katherine Valenta Darvesh ◽  
Patricia Axworthy ◽  
Richard Francis Langler
Keyword(s):  
Free Radicals ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Dimethyl Sulfide ◽  
Experimental Results ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Carbonium Ions ◽  
Moller Plesset ◽  
Better Than

Moller-Plesset molecular orbital calculations at the 6-31+G(d) level have been completed on substituted dimethyl sulfide-derived carbanions. The results are applied to the prediction of regiochemistry for chlorination of unsymmetrical sulfides. Notwithstanding the need for future improvements, regiochemical predictions based on stabilities of sulfur-substituted carbanions match experimental results better than earlier predictions based on stabilities of sulfur-substituted carbonium ions or sulfur-substituted free radicals. The present results suggest that the mechanism for the elimination step in the Pummerer rearrangement of a chlorosulfonium cation is an E 1cb-like process.

The Molecular and Electronic Structure of Tetrasulphur-dinitride; a Study by ab initio Molecular Orbital Methods and Photoelectron Spectroscopy

1982 ◽  
Vol 37 (9) ◽  
pp. 1061-1067 ◽  
Author(s):  
Michael H. Palmer ◽  
Woon Ming Lau ◽  
Nicholas P. C. Westwood
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Koopmans Theorem ◽  
Double Zeta ◽  
Reasonable Prediction ◽  
Excitation Processes ◽  
Molecular And Electronic Structure

Abstract The He (I) photoelectron spectrum of gaseous S4N2 is reported, and an assignment is made on the basis of the correlation with ab initio molecular orbital calculations. The latter, based upon the recently optimised geometry of Cѕ symmetry, used both a large basis set of greater than double zeta quality, together with configuration for both the ground state and the ionised states. The Koopmans’ Theorem order gives a reasonable prediction of the order of states for most of the low energy ionised states; beyond IP5 additional states involving excitation processes in conjunction with ionisation were computed. The numerical agreement between the observed IP’s and the CI value is reasonable.

Ab initio molecular orbital calculations of the infrared spectra of hydrogen bonded complexes of water, ammonia, and hydroxylamine. Part 6. The infrared spectrum of the water–ammonia complex

1991 ◽  
Vol 69 (4) ◽  
pp. 632-637 ◽  
Author(s):  
Geoffrey Andrew Yeo ◽  
Thomas Anthony Ford
Keyword(s):  
Hydrogen Bond ◽  
Infrared Spectrum ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Hydrogen Bond Energy ◽  
Hydrogen Bond Interaction ◽  
Intensity Changes ◽  
Hydrogen Bonded

The molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series of ab initio molecular orbital calculations, at the level of second order Møller–Plesset perturbation theory, using the 6-31G** basis set. The calculated wavenumbers and intensities have been compared with those calculated earlier for the respective monomers, and the wavenumber shifts and intensity changes rationalized in terms of the hydrogen bond interaction responsible for the stability of the complex.The calculated hydrogen bond energy of the complex has been compared with those of the linear water and ammonia dimers, reported in a previous publication, and the relative strengths of interaction of the three aggregates have been rationalized on the basis of the electron donor/acceptor capacities of the respective monomer units. Key words: ab initio, infrared spectrum, water, ammonia.

Single-centre molecular orbital calculations on third row hydrides - SeH2 and HBr

1975 ◽  
Vol 28 (5) ◽  
pp. 927 ◽  
Author(s):  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Single Centre ◽  
Minimal Basis ◽  
Heavy Atoms ◽  
Orbital Energies ◽  
Orbital Exponents

Single-centre molecular orbital calculations are reported for SeH2, and HBr using basis sets extending up to 5d orbitals centred on the heavy atoms. The choice of orbitals to be used in extending the basis set and the optimum values for orbital exponents are discussed. Orbital energies comparable with minimal basis set multicentre calculations are obtained for SeH2. The orbital energies are compared with those obtained experimentally by photoelectron spectroscopy. The results suggest that the single-centre method is worthy of consideration when studying the hydrides of the heavier elements.

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