Nomenclature in photon-chemical interactions and the retinoids

Since the 1970 s, the scope of the retinoid family of chemicals has evolved greatly, spurred by the focus on pharmacology. This progress has left the description of the structure of the retinoids in disarray. The initial system was defined by Karrer. Later, a set of structural rules was evolved by the IUPAC before the explosion in man-made retinoids. Later, Frickel introduced a set of systematic rules. None of these sets of rales contained any elements related to the electronic structure of the chemicals involved. This has left a void that requires attention. Section 5.5.12 will present a modification of the Frickel proposal that focuses on the relationship between the electronic and structural features of the retinoids of vision without detracting significantly from his systematic notation. 

Goodwin has provided a useful summary of the structural chemistry applicable to the retinoids of vision36. However, the book is not as comprehensive as needed to address all of the types of Vitamin A. He also refers to a separate essay on the structural notation he uses37. Taylor Ikawa have provided additional nomenclature, more semisystematic names and excellent information on laboratory evaluation techniques38. 

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