Ab initio calculations on large molecules using molecular fragments. Preliminary investigation of ethyl chlorophyllide a and related molecules

Abstract Ab initio SCF calculations using the molecular fragment method are reported for four molecules related to chlorophyll a, i.e., free-base porphine, magnesium porphine, magnesium chlorin, and ethyl chlorophyllide a. Molecular orbital structure, the “four-orbital model”, reactivity sites, and Mg···N interactions are discussed.