Conformational preferences of the fluoromethyl group in p-methylbenzyl fluoride and some derivatives

1980 ◽  
Vol 58 (12) ◽  
pp. 1178-1182 ◽  
Author(s):  
Ted Schaefer ◽  
Walter P. Niemczura ◽  
Rudy Sebastian ◽  
Leonard J. Kruczynski ◽  
Werner Danchura
Keyword(s):  
Benzene Ring ◽  
Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Conformational Preference ◽  
Orbital Theory ◽  
Carbon Bond ◽  
Carbon Carbon Bond ◽  
Conformational Preferences ◽  
Good Agreement

The coupling over seven bonds between 19F nuclei and protons in p-methylbenzyl fluoride and a series of ring-substituted derivatives is used to estimate the value for a conformation in which the C—F bond lies in a plane perpendicular to the benzene ring. The J method is then used to show that in CS2 solution, the Conformational preference of the fluoromethyl group is very weak in 3,5-dichloro-4-methylbenzyl fluoride and in 3,5-dibromo-4-methylbenzyl fluoride. The barrier to rotation about the exocyclic carbon—carbon bond is perhaps as large as 0.2 kcal/mol. In p-methylbenzyl fluoride, the C—F bond prefers a plane perpendicular to the benzene plane by ca. 0.9 kcal/mol. Good agreement is found with the Conformational preferences based on couplings over six or seven bonds between the methylene protons and the para ring or methyl protons. The deductions are compared with calculations at various levels of molecular orbital theory.

Applications of Quantum Chemistry. I. Energetics and Bonding in Conjugated Free Radical Chains

1971 ◽  
Vol 49 (2) ◽  
pp. 338-340 ◽  
Author(s):  
N. C. Baird
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Quantum Chemistry ◽  
Molecular Orbital ◽  
Heats Of Formation ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Carbon Bond ◽  
Bond Lengths ◽  
Carbon Carbon Bond

The heats of formation at 25 °C and the equilibrium carbon–carbon bond lengths are calculated by the neglect of nonbonded differential overlap molecular orbital theory for a series of conjugated, acyclic free radicals containing from one to nine unsaturated carbon atoms. The total bonding energies in the radicals exceed the values expected from polyene bond terms by 5–9 kcal/mol, depending on the length and branching of the chain.

Creation of a Simple Stable Enol. The Stabilizing Properties of the Diazonium Substituent

1979 ◽  
Vol 32 (7) ◽  
pp. 1401 ◽  
Author(s):  
MJ Ballard ◽  
WJ Bouma ◽  
L Radom ◽  
MA Vincent
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Electron Acceptor ◽  
Vinyl Alcohol ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Conformational Preferences ◽  
Alcohol System ◽  
Optimized Geometries

Ab initio molecular orbital theory is used to examine the effect of the diazonium substituent (N2+) on the keto-enol equilibrium in the acetaldehyde/vinyl alcohol system. The conformational preferences of the two isomers are examined, and optimized geometries obtained for the best conformers. The diazonium substituent is a strong π-electron acceptor and σ-electron acceptor, and accordingly destabilizes the keto isomer and stabilizes the enol isomer. The effect of the diazonium substituent is sufficiently large to make the enol isomer substantially lower in energy than the keto isomer.

Conformational preferences of the benzenedicarbaldehydes: an ab initio molecular-orbital, dipole-moment and Kerr-effect study

1984 ◽  
Vol 37 (3) ◽  
pp. 465 ◽  
Author(s):  
D Mirarchi ◽  
L Phillips ◽  
H Lumbroso ◽  
GLD Ritchie
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Kerr Effect ◽  
Dipole Moments ◽  
Effect Study ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Molecular Plane ◽  
Conformational Preferences ◽  
Kerr Constants

Ab initio molecular orbital theory at the STO-3G level is used to elucidate the structures and relative abundances of stable conformations of the three benzenedicarbaldehydes. In addition, new measurements of the infinite-dilution dipole moments and molar Kerr constants of these molecules as solutes in dioxan at 25�C are reported and analysed. The previously recognized inability of the simple group- additivity model to reliably predict the anisotropy in the polarizability of benzene-1,4-dicarbaldehyde is shown to be due to a redistribution of the polarizability in the molecular plane.

Keto-enol tautomerism. Relative stabilization of enol isomers

1978 ◽  
Vol 31 (6) ◽  
pp. 1167 ◽  
Author(s):  
WJ Bouma ◽  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Vinyl Alcohol ◽  
Energy Difference ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Conformational Preferences ◽  
Relative Stabilization ◽  
Alcohol System ◽  
Li Substitution

Ab initio molecular orbital theory is used to examine the effect of simple π-electron-accepting substituents (Li, BeH, BH2) on the keto-enol equilibrium in the acetaldehyde-vinyl alcohol system. The enol-keto energy difference is increased slightly by α-Li substitution and decreased to a near-zero value by a BH2 substituent. The results are rationalized in terms of geminal interactions. The conformational preferences of substituted acetaldehyde systems (XCH2CHO; X = Li, BeH, BH2, CH3, F) are discussed. Three classes of rotational potential functions are distinguished on the basis of the σ-electron-donating or -accepting nature of the substituent.

The molecular orbital theory of chemical valency VIII. A method of calculating ionization potentials

1951 ◽  
Vol 205 (1083) ◽  
pp. 541-552 ◽  
Keyword(s):  
Molecular Orbital ◽  
Empirical Method ◽  
Ionization Potentials ◽  
Orbital Method ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Atomic Orbitals ◽  
Usual Form ◽  
Semi Empirical ◽  
Good Agreement

An analysis of the ‘linear combination of atomic orbitals’ approximation using the accurate molecular orbital equations shows that it does not lead to equations of the form usually assumed in the semi-empirical molecular orbital method. A new semi-empirical method is proposed, therefore, in terms of equivalent orbitals. The equations obtained, which do have the usual form, are applicable to a large class of molecules and do not involve the approximations that were thought necessary. In this method the ionization potentials are calculated by treating certain integrals as semi-empirical parameters. The value of these parameters is discussed in terms of the localization of equivalent orbitals and some approximate rules are suggested. As an illustration the ionization potentials of the paraffin series are considered and good agreement between the observed and calculated values is found.

Bonding in Transition Metal Silyl Dimers. Molecular Orbital Theory

1989 ◽  
Author(s):  
Alfred B. Anderson ◽  
Paul Shiller ◽  
Eugene A. Zarate ◽  
Claire A. Tessier-Youngs ◽  
Wiley J. Youngs
Keyword(s):  
Transition Metal ◽  
Molecular Orbital ◽  
Molecular Orbital Theory ◽  
Orbital Theory
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