C-H...[[pi]] INTERACTION OBSERVED IN COMPLEXES OF SURFACTANT MOLECULES WITH AROMATIC COMPOUNDS. Keiju Sawada^{[[daggerdbl]]}, Yuji Ohashi^{[[daggerdbl]]}, Nahoko Iimura^{[[daggerdbl]]} and Hirotaka Hirata^{[[daggerdbl]]}, "Department of Chemistry, Tokyo Institute of Technology, Japan and ^{[[daggerdbl]]}Niigata College of Pharmacy, Japan

A C-H...[[pi]] interaction has been found between surfactant molecules and aromatic compounds. Various complexes were obtained from an aqueous solution with cationic surfactants, such as cetyl-(C_l6H₃₃N(CH₃)₃,CTAB), myristil-(C_l4,MTAB), lauril-(C_l2,LTAB) and decyl(C₁₀,DTAB) trimethylammoniumbromide, and aromatic compounds. The griding of the two compounds in a mortar gave the same complexes as obtain in the solution.

In order to examine the interaction between surfactant molecules and aromatic compounds, we tried to form the complexes of CTAB, MTAB, LTAB, DTAB with biphenyl (C₁₀H₈) which has no functional groups. After many trials, all the complex crystals were successfully obtained. Moreover, the same complexes were formed by griding in a mortar. The analyzed structures of the complexes clearly suggest a special interaction, C-H..[[pi]], between the alkyl group and phenyl rings. This interaction should be a driving force of these formation.