Crystal cohesion and conformational energies. part 26 of Topics in current physicsedited by R. M. Metzger

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

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Symmetrically substituted silanes: (XH2C)2SiH2, (XH2C)2SiX2, (X2HC)2SiH2 and (X2HC)2SiX2 with X = F, Cl or Br. Conformational energies, structures and torsional force constants obtained by molecular-mechanics calculations

Journal of Molecular Structure THEOCHEM ◽

10.1016/s0166-1280(05)80020-x ◽

1995 ◽

Vol 372 (2-3) ◽

pp. 275-284

Author(s):

Tore H. Johansen ◽

Reidar Stølevik

Keyword(s):

Molecular Mechanics ◽

Force Constants ◽

Molecular Mechanics Calculations ◽

Conformational Energies

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Calculation of molecular geometries, relative conformational energies, dipole moments, and molecular electrostatic potential fitted charges of small organic molecules of biochemical interest by density functional theory

Journal of Computational Chemistry ◽

10.1002/jcc.540161206 ◽

1995 ◽

Vol 16 (12) ◽

pp. 1483-1506 ◽

Cited By ~ 64

Author(s):

Alain St.-Amant ◽

Wendy D. Cornell ◽

Peter A. Kollman ◽

Thomas A. Halgren

Keyword(s):

Density Functional Theory ◽

Electrostatic Potential ◽

Density Functional ◽

Molecular Electrostatic Potential ◽

Organic Molecules ◽

Dipole Moments ◽

Functional Theory ◽

Small Organic Molecules ◽

Conformational Energies

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Conformational features of bisphenol-A polycarbonate

Canadian Journal of Chemistry ◽

10.1139/v85-018 ◽

1985 ◽

Vol 63 (1) ◽

pp. 103-110 ◽

Cited By ~ 9

Author(s):

P. R. Sundararajan

Keyword(s):

Bisphenol A ◽

Repeat Unit ◽

Methyl Groups ◽

Bisphenol A Polycarbonate ◽

Carbonate Group ◽

Torsion Angles ◽

Thermal Crystallization ◽

Lennard Jones ◽

Empirical Force Field ◽

Conformational Energies

Conformational energies have been estimated for the segments of the bisphenol polycarbonate chain, using the Lennard–Jones and Hill's empirical force field type of functions. It is found that the conformation of the carbonate group, defined by the torsion angle ζ, is restricted to the range of 45° to 65°. The rotations χ and χ′ of the methyl groups also show similar limited flexibility. However, accessible conformations of the diphenyl propane (DPP) segment, defined by torsion angles [Formula: see text] and ψ, span a wide area of the [Formula: see text] surface, with the restriction that the rotations [Formula: see text] and ψ be synchronized such that [Formula: see text] or 270°. These features explain the slow thermal crystallization behaviour of the polycarbonate chains. The variability of the conformations of the repeat unit is illustrated with a series of figures.

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