Definitions:
" frequently with distinguishing greek letter. each of a number of fragrant unsaturated isomeric ketones which are products of the breakdown of carotenoids and occur naturally in some essential oils; specifically (more fully ""β-ionone"") a compound that arises as a product of ψ-ionone in the synthesis of vitamin a.

in full ""ψ-ionone"". an acyclic compound isomeric with α- and β-ionone which can be cyclized to form those compounds and is used in the synthesis of vitamin a.

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