= Pyridoxine
<Pyridoxine> is the <alcohol> form of <Vitamin B6>, with <molecular formula> $\mathrm{C_8H_{11}NO_3}$. Its <pyridine> ring has a methyl group at position 2, a <hydroxyl group> at position 3 and hydroxymethyl groups at positions 4 and 5.<Pyridoxine in ChEBI>[CHEBI:16709, Definition and Formula]{ref}
At position 4, <pyridoxine> differs from the <aldehyde> <pyridoxal> and the <amine> <pyridoxamine>. Replacing $\mathrm{-CH_2OH}$ by $\mathrm{-CHO}$ changes the formula by two hydrogen atoms; replacing it by $\mathrm{-CH_2NH_2}$ changes both the <oxygen> and <nitrogen> counts. This provides a concrete structural meaning for the three names, beyond their membership of the same vitamin family.
The distinction also matters for <biochemistry>. <Pyridoxal phosphate> and <pyridoxamine phosphate> are active <coenzyme> forms; free <pyridoxine> is not simply another name for either phosphorylated molecule.<Vitamin B6 Fact Sheet for Health Professionals by the Office of Dietary Supplements>[Introduction, chemical forms and active coenzymes]{ref} For example, an experiment comparing equal molar amounts of two B6 forms holds the number of molecules constant, while their functional groups and ability to enter a particular reaction can still differ. Equal mass would additionally fail to hold molecular amount constant because the forms have different <molar mass> values.
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