with the longer single bonds in one location and the shorter double bond in another (See Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History section below). The model for benzene consists of two resonance forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization. Principal uses Because of the unique shapes, reactivities, properties, and bioactivities that they engender, cyclic compounds are the largest majority of all molecules involved in the biochemistry, structure, and function of living organisms, and in the man-made molecules (e.g., drugs, herbicides, etc.) through which man attempts to exert control over nature and biological systems. Synthetic reactions Important general reactions for forming rings There are a variety of specialized reactions whose use is solely the formation of rings, and these will be discussed below. In addition to those, there are a wide variety of general organic reactions that historically have been crucial in the development, first, of understanding the concepts of ring chemistry, and second, of reliable procedures for preparing ring structures in high yield, and with defined orientation of ring substituents (i.e., defined stereochemistry). These general reactions include: Acyloin condensation; Anodic oxidations; and the Dieckmann condensation as applied to ring formation. Ring-closing reactions In organic chemistry, a variety of synthetic procures are particularly useful in closing carbocyclic and other rings; these are termed ring-closing reactions. Examples include: alkyne trimerisation; the Bergman cyclization of an enediyne; the Diels–Alder, between a conjugated diene and a substituted alkene, and other cycloaddition reactions; the Nazarov cyclization reaction, originally being the cyclization of a divinyl ketone; various radical cyclizations; ring-closing metathesis reactions, which also can be used to accomplish a specific type of polymerization; the Ruzicka large ring synthesis, in which two carboxyl groups combine to form a carbonyl group with loss of and ; the Wenker synthesis converting a beta amino alcohol to an aziridine other reactions, such as an amino group reacting with a hydroxy group, as in the biosynthesis of solanine Ring-opening reactions A variety of further synthetic procedures are particularly useful in opening carbocyclic and other