c20h28o

from The Collaborative International Dictionary of English v.0.48

Retinal \Ret"i*nal\, n. (Chem.)
   A retinoid compound ({C20H28O}), closely related to vitamin
   A, which is a component of the visual pigments in the eye. It
   is also called {retinaldehyde} and {vitamin A aldehyde}.
   [PJC]

from The Collaborative International Dictionary of English v.0.48

vitamin A2 \vitamin A2\ n.
   dehydroretinol ({C20H28O}), one of the substances also called
   {vitamin A}. It has about 40% of the bioactivity of vitamin
   A1.

   Syn: dehydroretinol.
        [WordNet 1.5 +PJC]

[email protected]