THE IMPORTANCE OF TRANS-HYDROGEN INTERACTIONS IN SIMPLE FORCE FIELDS
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Publisher:Ohio State University
“Neither a simple valence nor a Urey-Bradley force field (UBFF) will satisfactorily fit the observed frequencies of ethylene. Shimanouchi has argued, from a classical consideration of bond flexibility, that an extra force constant should be added to the UBFF, and indeed, inclusion of this additional parameter allows a good frequency fit in ethylene. We have used a UBFF with the Shimanouchi extension in an investigation of a large number of simple ethylenie derivatives but have found it impossible to obtain a consistent picture. However, a simple UBFF with the sole addition of a quadratic cross term coupling the trans hydrogen-bending coordinates gives an equally satisfactory fit to the ethylene frequencies, and moreover, the numerical value of this force constant can be transferred logically within the series of bromo ethylenes. This trans-interaction model has been extended to ethane, propane, and other simple molecules.”
Author Institution: Chemical Physics Research Laboratory, The Dow Chemical Company
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