Part of the photosynthetic systems in green plants. Generally speaking, it can be considered as a magnesium complex of a porphyrin in which a double bond in one of the pyrrole rings (17-18) has been reduced. A fused cyclopentanone ring is also present (positions 13-14-15).In the case of chlorophyll a, the substituted porphyrin ligand further contains four methyl groups inpositions 2, 7, 12 and 18, a vinyl group in position 3, an ethyl group in position 8 and a -(CH2)2CO2R group (R = phytyl, (2E)-(7R, 11R)-3,7,11,15-tetramethylhexadec-2-en-1-yl) in position 17. In chlorophyll b, the group in position 7 is a -CHO group. In bacteriochlorophyll a the porphyrin ring is further reduced (7-8), andthe group in position 3 is now a -COCH3 group. In addition, in bacteriochlorophyll b, the group in position 8 is a =CHCH3 group.
