of the complex molecules:

COO.C_{20}H_{39} COO.C_{20}H_{39}
/ /
MgC_{31}H_{29}N_{3}-COO.CH_{3} MgC_{32}H_{28}O_{2}N_{4}-COO.CH_{3}
|\ Chlorophyll _b_
NH-CO
Chlorophyll _a_

The chlorophylls are unstable compounds, readily acted upon by acids or
alkalies, and by the enzyme chlorophyllase, which splits off the phytyl
alcohol group. The progressive action of acids and of alkalies in breaking
down the molecule, and the products of its oxidation and reduction, have
served to establish the chemical composition of the compound in each case.
Because of the importance of these pigments in the whole metabolic
processes of the plant, it seems to be desirable to consider the nature of
these reactions in some detail, as follows:

=Decomposition of the Chlorophylls by Alkalies.=--The first action of
dilute alkalies on the chlorophylls is to split off, by hydrolysis, the
alcoholic groups of the esters, producing the crystalline tri-basic acids,
or _chlorophyllins a_ and _b_. Each of these chlorophyllins exists in two
forms, the normal and the iso, in which the attachment of the COOH groups
to the other groups in the molecule is in different positions. Hence,
chlorophyll _a_ yields chlorophyllin _a_ and isochlorophyllin _a_, and
chlorophyll _b_ yields chlorophyllin _b_ and isochlorophyllin _b_, all four
of which are tri-basic acids.

These compounds, when heated with alkalies, split off carbon dioxide in
successive stages, losing one COOH group at each step, thus yielding a
series of simpler compounds of the following types: First, di-basic acids;
second, monobasic acids; and finally, _aetiophyllin_, a compound in which no
COOH group is present. In all of these compounds, derived from chlorophylls
by the action of alkalies, the Mg remains in the molecule, and all the
Mg-containing derivatives from the chlorophylls are known as "phyllins." At
the stage at which only one COOH group remains in the molecule, only one
group arrangement is possible, and the derivatives from chlorophyllin _a_
and isochlorophyllin _b_, and those from chlorophyllin _b_ and
isochlorophyllin _a_, are identical. At the final stage, the derivatives
from all four forms are identical. This may be graphically illustrated by
the following diagram indicating the progressive decomposition of the two
chlorophylls under t