ESTIMATE OF A RELATIONSHIP BETWEEN THE NUMBER OF ATOMS AND THE VOLUMES OF THE UNIT CELLS OF ORGANIC-COMPOUNDS

A systematic analysis concerning the relationship between the cell vol umes and the numbers of atoms in the unit cells of organic molecules w ith the general formula C(a)H(b)F(c)N(d)O(e) (where c, d, e greater-th an-or-equal-to 0) has been carried out using the Cambridge Structural Database as a source of data and search tool. The results suggest that the H atoms make a significant contribution to the total occupied vol ume of the unit cell. Although that influence is clearly not uniform a nd differs from one compound to another, it is possible to obtain two new relationships which take into account this participation. It is al so clear that the inter- and intramolecular interactions, such as hydr ogen-bonded contacts and pi-pi interactions, produce a decrease in the non-occupied volume of the cell and a lower average volume per atom.