Density Functional Study of the Structure and Infrared Spectrum of Ethyl Chlorophyllide (A)

A DFT/B3LYP calculation using the 6-31G(d) basis set was performed to obtain the structure, normal vibration frequencies, and absolute IR intensities of ethyl chlorophyllide (A). The calculated structural parameters agree well with the experimental X-ray diffraction data. The role of saturated substituents in stabilization of radical ion states of chlorophyll is discussed. The effective force field of ethyl chlorophyllide (A) was obtained in independent and dependent internal coordinates. The IR vibrational spectrum is modeled. The experimental IR spectrum of chlorophyll (A) is interpreted on the basis of the calculation.