Adopted by Molecular Mechanics as a model for describing PES for all degrees of freedom of a molecular system. In this molecule, all pieces of experimental evidence say that it is planar with wide amplitude ring puckering. On the other hand, according to the precise Dreiding molecular models, the planar form of this molecule is very unstable, a slight jiggling of the model causing a sudden change to boat conformation. Unfortunately, many experimental NMR results of dihydrobenzene, dihydronapthalene, and dihydroanthracens were interpreted on the preconceived notion that planar forms are unstable as predeicted by the hand-held models and as indicated by solid state structures that were influenced by crystal packing forces. However, no molecule is strain free.
Treatment relies heavily on availability of experimental data for parameterization.
In the simplest force fields, perhaps a dozen or so parameters are necessary to describe the alkanes. Such a force field gives a reasonable approximation to molecular structures and E differences, but the values obtained from such a force field are clearly inferior to values measured experimentally To better reproduce the available exptal data, further optimization of the parameters or the introduction of more of them by modifying the equations that make up the force field might be considered. EFF methods are interpolations and sometimes extrapolations of existing data. Pictorial diagram of various components. Each modification means a reoptimization.