Chlorophyll structural formulas

The isoprene unit exists extensively in nature, it is found in tcrpcncs. camphors, dilerpenes ic.g.. abietic acidi. vitamins A and K. chlorophyll, and other compounds isolated front animal and plant materials. The correct structural formula for isoprene was first proposed in 1884. 

The structural formula in Fig. 4 indicates the present concept of the chemical structure of chlorophyll-a (the numbering system is that of Hans Fischer). Chlorophyll-b differs from chlorophyll-a with respect to the group at position 3. The methyl group in chlorophyll-a is replaced by an aldehyde group (—CHO) in chlorophyll-b. 

Many of the Lewis structures in Chapter 9 and elsewhere in this book represent molecules that contain double bonds and triple bonds. From simple molecules such as ethylene and acetylene to complex biochemical compounds such as chlorophyll and plastoquinone, multiple bonds are abundant in chemistry. Double bonds and triple bonds can be described by extending the orbital overlap model of bonding. We begin with ethylene, a simple hydrocarbon with the formula C2 H4. 

The canonical form for chlorophyll ti is R =CHt when substituted in the following formula. For chlorophyll l>. R = CHO. These structures have been established hy a long series of degradation studies mainly by R. Willsriilter. Hans Fischer and Iheir collaborators and by synthetic studies by Fischer. 

There followed a series of basic studies on the chemistry of these pigments which culminated in the establishment of the structure of heme in 1928 and of chlorophyll in 1939. The work of Nencki, Marchlewski, Ktister, and Willstatter demonstrated that heme and chlorophyll were built upon the same basic tetrapyrrole plan, although one, the chlorophyll, was an Mg complex, and the other, the heme, was an iron complex (Fig. 15, formulas VI and VIII). It remained for Fischer and Conant and their co-workers to determine the composition and positions of the side chains attached to the pyrroles and to make clear the differences in the structure between these two pigments. 

Willstatter (1872-1942) Fundamental structural studies on chlorophyll (and its empirical formula) and other plant pigments Recognition of central metal ion of Mg bound to four nitrogens 1915 Nobel Prize in Chemistry [43]... 

Willstatter, who first elucidated the formula of chlorophyll, ascribes little biological significance to the haemoglobin and chlorophyll relationship. Immediate utility and not biological tradition has determined the structure of each compound. But these conclusions were reached before the universal distribution of cytochrome was demonstrated. 

Fig. 5.3. Chemical structure of chlorophyll a (note the long phytyl side chain) and skeleton formulae of 8-carotene and the carotenol lutein.

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