Torsion/torsional

Major cause Torsional Torsional Torsional + steric Steric... 

Torsion. Torsional deformation of an isolated equilibrium str ucture means twisting it so as to change the dihedral angle connecting two atoms. The dihedral angle... 

EFF (Empirical force field) [186] has been designed just for modeling hydrocarbons. It uses the quartic anharmonic potential for the bond stretching, and the cubic anharmonic for the valence angle bending. No out of plane or electrostatic terms are involved, although the cross terms, except torsion-torsion and bend-torsion ones, are included. 

The general method for analyzing the spectra is the same for molecules with two methyl groups or tops, although now a multiplet pattern appears instead of a doublet. The Hamiltonian contains, in addition, terms for torsion-torsion interaction [ Vl2, V[2, of Eq. (3)], which are additional constants to be determined. 

Improper torsion Torsional function applied to four atoms not connected by consecutive bonds. Often used to enforce planarity in conjugated systems. 

Notation Vn Polynomial of order n P (cos) polynomial of order n in cosine to the angle cos(nS) Fourier term(s) in cosine to the angle Exp-6 exponential + R n - m R + R Lennard-Jones type potential quad electric moments up to quadrupoles polar polarizable fixed not a variable imp. improper torsional angle ss stretch-stretch bb bend-bend sb stretch-bend St stretch-torsional bt bend-torsional tt torsional-torsional btb bend-torisional-bend. 

The energy of valence interactions accounts for bond stretching (bond), valence angle bending (angle), dihedral angle torsion (torsion), and inversion, also called out of plane interactions (oop) ... 

Interactions between close electronegative atoms in molecules have not been very well smdied. There are, of course, both strong van der Waals and electrostatic interactions between them. These interactions may require potentials that are more accurate at short distances than those used in MM4. The f or higher term in the dispersion interaction and/or the quadrupole interactions in the electrostatics may be significant here. Whatever this interaction may turn out to be, it seems to be accounted for fairly well by a torsion-torsion interaction in MM4. 

In order to reproduce this external anomeric torsional effect in MM4, a torsion-torsion interaction (between the 2,3,4,5 and 3,4,5,6 bonds in Structure 8) was used. It was worked out so that the results on dimethoxymethane and on methoxyeth-oxymethane as obtained by MMP2 calculations were reproduced with MM4. (It is... 

Rotationssinn rotational sense, sense of rotation Drehtisch micros rotating stage Drehung/Torsion torsion Drehwalze (Roller-Apparatur) roller Drehzahl... 

Torsion Torsion and torsion stress involve rotational loads on a material. A section of the material must be retrained in order for a torsional load to be appUed. A torsional failure on a shaft will create a somewhat spiraled break compared to a bending failure for the same material. Compare the difference in fractures between a piece of chalk when you simply bend it in your hands and when you hold one end tight and twist the other end. 

OIT-diagonal terms (cross terms) Bend-stretch Off-diagonal terms (cross terms) Stretch-stretch Bend-stretch Bend-bend Torsion-stretch Torsion-bend Torsion-torsion Bend- torsion - bend and higher terms... 

MM3 is able to treat vibrational frequencies well for conjugated systems since bond stretching and torsional parameters are calculated from the n bond orders. An exception to this occurs for bending frequencies, especially in heterocyclic conjugated compounds. These can be well treated only with the addition of explicit off-diagonal elements in the force constant matrix, and this has been done with the MM4 FF. MM4 also scales the V3 and V4 torsional terms to n bond orders, and the addition of stretch-stretch and torsion-torsion cross terms allows an even more accurate calculation of vibrational... 

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