E O S , U L . V A V I L O V A 2 8 , M O S C O W -V -3 1 2 , U . S . S . R .
Mechanical Model of MoleculesThe word 'molecule' may be used in two different meanings. Speaking about a 'common salt molecule' we have in mind the finest representative of this substance: one sodium atom and one chlorine atom make up a common salt molecule. However, a common salt particle consisting of one sodium and one chlorine atom does not exist in nature. When dissolved, this substance dissociates into ions. In solids, each positively or negatively charged ion has six neighbouring ions of the opposite sign located at equal distances. The same happens in the melted substance, the only difference being that the co-ordination number of six is realized here 'on the average'.Speaking about a 'naphthalene molecule' we also mean the smallest representative of this substance, but unlike the previous example a naphthalene molecule, composed of ten carbon atoms and eight hydrogen atoms, exists as a separate particle in solids, solutions, or melts and in a gaseous state.Most inorganic substances behave as common salt. In inorganic substances we do not have, as a rule, to subdivide interactions into valence and non-valence (non-bonded) types. On the contrary, in the okerwhelming majority of organic substances this distinction is completely obvious.Experimental studies of the structure and properties of organic molecules and crystals, as well as practical work on chemical synthesis, testify that the model of an organic molecule in the form of a set of atoms linked by 'springs' in conformity with a valence scheme is a very good approximation to its actual structure. This model, which may quite appropriately be called a mechanical model, has great predictability in almost all the spheres of physical chemistry and can be equally well applied to many problems of synthetic organic chemistry. About 30 years ago, approximarely at the same time and independently of one another, Hill,1 Westheimer,2 and the present author3 showed that a mechanical model may acquire quantitative characteristics. However, its 'computation value' for predicting the geometry of molecules and crystals and for calculating their properties was demonstrated only after the emergence of computers.The mechanical model is based on the concept that each atom in a molecule calculated the path of isomerization. The angles of rotation about the C-3-C-4 and C-2-C-3 bonds are plotted along the rotation axes. The displacements of 7 2 V. G . Dashevsky and A. A. Lugovsky, J . Mol. Structure, 1972, 12, 39. 153
