Noncyclic

Noncyclic is an adjective used to describe something that does not form or belong to a cycle. In mathematics and geometry, noncyclic refers to concepts that are not generated by or constrained to a single cycle. For example, a noncyclic group is a group that cannot be generated by one element; the Klein four group, isomorphic to Z2 × Z2, is noncyclic, while Z4 is cyclic. A noncyclic quadrilateral is a four-sided figure whose vertices do not all lie on a common circle, in contrast to a cyclic quadrilateral.

In chemistry, noncyclic describes molecules that lack ring structures. Noncyclic alkanes, such as hexane, are straight- or branched-chain hydrocarbons, as opposed to cyclic alkanes like cyclohexane. The term also appears in polymer science and medicinal chemistry to denote non-ring-containing architectures.

In biology and biochemistry, noncyclic photophosphorylation refers to the light-dependent electron transport in photosynthesis that proceeds from water through photosystem II and photosystem I to NADP+, producing both ATP and NADPH, whereas cyclic photophosphorylation yields ATP alone by electrons cycling back to the photosystem. In general usage, noncyclic contrasts with cyclic, acyclic, and circular concepts.