@M04021@ having a carbon–carbon double bond anywhere in the @B00574@ chain. @G02644-1@ (term not recommended) designates the enoses that are generated by formal @E02038@ of the hemiacetal hydroxy group and an adjacent hydrogen atom. Thus @G02644-2@ are cyclic @E02124@. Unsaturated hexoses, for example, are called hexenoses, e.g. the hex-1-enopyranose derived from d-glucopyranose):