ORIENTATIONAL DISORDER OF SOME ORGANIC MOLECULAR CRYSTALS STUDIED BY ATOM-ATOM POTENTIALS. Chitra Samanta, Dept. of Physics, Jadavpur University, Calcutta, India

Systematic analysis of molecular geometry and conformation were studied by atom-atom potential method.

The vander waal's inter molecular attraction concept leads to the pairwise non-bonded interaction potentials. Concerning the arrangements of atoms in a regular distribution the potential of Bucking ham's type -AA/r⁶+Be Alpha r/r^m were applied to the study of organic molecular crystals.

The universal potential parameters, AA,B Alpha m are used from those of Giglio, E².

The evaluation of lattice energies (Kcal/mol) with rotation of the molecules about an axis passing through the centre of gravity and normal to the molecular plan yields the interesting results regarding the confirmation of the molecular disorder. The following crystals were studied:-

Crystals Molecular Formula Cell Parameters

1. 1,2 Dichloro- C₂H₄Cl₂ Ao=4.66¡ [[Alpha]]

ethane

2. P- nitrobenzoic NO₂C₆H₄COOH AO=12.97¡ A

acid BO=5.07¡ A

CO=21.43¡ A

3. Pentaerythritol C(CH₂OH)₄ AO=6.083¡ A

CO=8.726¡ A

Ref:

1.Acta Cryst., Roychowdhury and Basak, B31, 1969.

2.Acta Cryst., Govezzotti, A and Simonetta, M, 17.559 1964.