Abstract: In this paper the compounds containing cyclic tri-hydrogen group are investigated by FTIR, PMR, GCand ab initiu calculation. Triformol as a model molecule of cyclic 3Hg roups was calculated by ab initio method. It is explored by the results of ab initio electrostatic potential calculations that there is a positive electropotential region at the direction of the three axial hydrogen atoms. This points out the collective effect of the cyclic 3Hgroup and the cause for easily understanding its larger interaction with the atom carrying negative.FTIRspectra of solution of diphenyl ketone in hexane and paraldehyde are determined. The peak of streching mode of C=O group shifts 7. 9 cm^-1to the low frequency in the latter case. PMR peak of CHfor paraldehyde in acetone solution shifts 0. I 5 ppm up to the high field in comparison with that in CC₁₄and CHC₁₃solution.Evidences of 3Hgroup for 666 are also obtained by FTIR, PMR. All the experimental evidences support the results of computation and confirm the existance of cyclic 3Hgroups.

Key words: Tri-hydrogen group, Intermolecular force, Electrostatic potential, Heat of solution