Influence of rotational energy

The occurrence of the NH4+ ion in the highly symmetrical sodium chloride and caesium chloride structures is seemingly inconsistent with its tetrahedral configuration and can be explained only on the assumption that the ion effectively acquires spherical symmetry by free rotation under the influence of the energy of thermal agitation. We shall encounter many other examples of structures in which ions or molecules are in free rotation, either at all temperatures or above a certain transition temperature all are examples of yet a further type of defect structure. 

In order to take the influence of internal energy into account in a simple fashion, Menzinger and Wolfgang (112) suggest that vibrational states changes with temperature. 

Fig. 66. Influence of rotation on an energy curve V (p) of a diatomic molecule. Dissociation by rotation.

The experimental methods for polarizability determination based on the Stark effect use the displacements and splitting of rotational energy levels of small molecules under the influence of an external electric field [11-14]. The usual accuracy of these methods is in the range of 3-10 %. 

Glennon and co-workers reported an exploration of the influence of intra- and intermolecular interactions in carbohydrate modeling in 1994. On the basis of earlier examinations.> of rotational energy profiles, they concluded that tlje exo-anomeric rotational energies could be adequately repi duced with the default AMBER threefold rotational term for C-0 bonds (equation 14). 

Stereochemistry. Cyclohexane can exist ia two molecular conformations the chair and boat forms. Conversion from one conformation to the other iavolves rotations about carbon—carbon single bonds. Energy barriers associated with this type of rotation are low and transition from one form to the other is rapid. The predominant stereochemistry of cyclohexane has no influence ia its use as a raw material for nylon manufacture or as a solvent. 

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