Acetone and cyclopentane make a minimum boiling homogeneous binary azeotrope with mole ratio 2:3. Some characteristic vibrational modes, as well as 1 H NMR signals change due to the azeotrope formation. The extend of interaction of these molecules causes significant changes on some vibrational modes involved and 1 H NMR signals show some changes on their position. In this work the FTIR and 1 H NMR spectra of pure acetone, pure cyclopentane and corresponding azeotrope were recorded, mutual influences resulting from azeotrope formation have been analyzed, and spectral changes has been discussed. The unit-structure of cluster have been deduced, based on mole ratio, boiling point depression of constituents, and comparison between the spectra obtained by FTIR and 1 H NMR techniques.