Conformational energy parameter

The configurational characteristics of PODME are established by calculations based on the RIS model. By using an appropriate set of conformational energy parameters, the characteristic ratio and the dipole moment ratio are evaluated. 

Calculations have been carried out for poly[(5)-l-methylpropyl vinyl ether] and poly[(S)-2-methylbutyl vinyl ether] using properly estimated conformational energy parameters. The characteristic ratios C obtained are shown in Figure 6(a). For the former polymer, large enhancement in Cqo is predicted both in the isotactic (Pr>0.8) and in the syndiotactic Pr<0.2) region. 

Lewis, P. N., F. A. Momany, and H. A. Scheraga. 1973a. Energy Parameters For Polypeptides Conformational Energy Analysis Of The N-Acetyl N -Methyl Amides of The Twenty Naturally Occurring Amino Acids. Isr. J. Chem. 11, 121-152. 

The MM2 force field3 is probably the most extensively parameterized and intensively used force field to date. It reproduces a variety of molecular properties such as geometry, dipole moments, conformational energies, barriers to rotation and heats of formation. Of particular importance for calculations of amines is that MM2 treats lone pairs on sp3 nitrogens (and oxygens) as pseudo atoms with a special atom type and parameters. A closely related force field, MM2 7, was derived from MM2 by Osawa and Jaime. MM2 uses the same potential functions as MM2, but employs a different set of parameters in an attempt to better reproduce barriers to rotation about single C—C bonds. 

Torsional parameters. These (in conjunction with hydrogen bonding parameters, see below) were chosen to reproduce the ab initio conformational energies of the model compounds. 

Torsional parameters and VdW parameters for internal hydrogen bonds in the N—C—N moiety were obtained by fitting the ab initio rotational profiles of methylenediamine (MDA, 15) and /V-methylmelliylenediamine (NMMDA, 16). A comparison of relative conformational energies between ab initio and MM2 results for 15 and 16 is provided in Table 6. Bond length correction terms for inner and outer C—N bonds (K, K2 and... 

As in the case of the MM2 force field, parameterization of MM3 for amines was based mainly on experimental data with occasional references to ab initio calculations, mainly to evaluate relative conformational energies and derive appropriate torsional parameters. As mentioned above, one notable difference between the two force fields is the removal of lp on sp3 nitrogens from MM3. This simplifies the treatment of vibrational spectra and allows for a realistic treatment of nitrogen inversion which could not be handled by MM2. As usual with MM3, parameterization was aimed at reproducing a variety of molecular properties such as structure, steric energy, dipole moments, moments of inertia, heat of formation and vibrational spectra. A complete list of MM3 parameters for amines is provided in Reference 6. 

In this paper, the effect of the pseudopotential term, arising from the quantum mechanical correction to classical mechanism (V ), on the torsional levels of hydrogen peroxide and deuterium peroxide is evaluated. The V operator, depends on the first and second derivatives with respect to the torsional coordinate of the determinant of the g inertia matrix and on the first derivatives of the B kinetic energy parameter of the vihrational Hamiltonian. V has heen determined for each nuclear conformation from the optimized coordinates obtained using MP2/AUG-cc-pVTZ ah initio calculations. 

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