Conformational analysis fitting, molecular

A number of theoretical and experimental approaches toward conformational analysis of crown thioethers have been developed. A molecular mechanics force field for thiols and thioethers, developed from crystal structures and experimental data <87JST(I59)I37> reproduces molecular structures and provides reasonable fits for both the energy differences between conformers and barriers to internal rotation. Thioethers with gauche placement at carbon-sulfur bonds were calculated to be 0.69 kJ mol more stable than those with anti placement, in agreement with earlier SCF-MO calculations <85MP33l). 

Vibrational spectroscopy has played a very important role in the development of potential functions for molecular mechanics studies of proteins. Force constants which appear in the energy expressions are heavily parameterized from infrared and Raman studies of small model compounds. One approach to the interpretation of vibrational spectra for biopolymers has been a harmonic analysis whereby spectra are fit by geometry and/or force constant changes. There are a number of reasons for developing other approaches. The consistent force field (CFF) type potentials used in computer simulations are meant to model the motions of the atoms over a large ranee of conformations and, implicitly temperatures, without reparameterization. It is also desirable to develop a formalism for interpreting vibrational spectra which takes into account the variation in the conformations of the chromophore and surroundings which occur due to thermal motions. 

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