CH/π interaction in the crystal structure of organic compounds.: A database study

The CH/pi interaction is a weak molecular force occurring between CH groups and pi-groups. A study was carried out by use of the Cambridge Structural Database in order to obtain insights into the nature of the CH/pi interaction and to examine its role in the crystal packing. The proportion of organic molecules bearing at least one CH/pi interaction in their crystal structures has been found considerable. The CH hydrogen atoms tend to point toward the center of the aromatic ring. A number of short CH/pi distances have been shown in the crystal structures of organic compounds. Moreover, the mean CH/pi distance decreases as the acidity of the CH group increases. These results suggest that the CH/pi interaction is not simply due to the dispersion force but involves other types of interactions, which are orientation-dependent and effective at wider ranges. It was suggested that the CH/pi interaction constitutes one of the important factors in controlling, the crystal packing of molecules.