Labile chemical bonds generate an intermediate state of chemical reaction and exhibit an ultimate of orbital interaction forming a chemical bond. Detailed investigation of such bonds construct a solid basis for understanding the origin of chemical bond and bond formation. Herein the author describes electronic structures of labile chemical bonds such as hypervalent bonds, small-cyclic alkyne, and intermediate states of C-C bond cleavage, derived by experimental X-ray electron density distribution（EDD）analysis. A novel approach is also presented for analyzing the mechanism of catalytic reaction based on EDD analysis closely related to spectroscopy and theoretical calculations.