cyclobutanes

Cyclobutanes are a class of cycloalkanes with a four-membered ring and the formula C4H8. The parent compound is cyclobutane, a saturated hydrocarbon. Many derivatives exist in which one or more ring hydrogens are replaced by substituents.

Structure and properties: The four carbons form a square-like ring; however, the ring is not flat in most cases. To relieve angle strain, cyclobutane adopts a puckered conformation that reduces torsional strain compared with a planar square. The ring carries substantial strain relative to larger cycloalkanes, which influences its reactivity. Cyclobutane is a colorless, volatile, flammable hydrocarbon; derivatives vary in physical properties.

Synthesis and reactions: A principal route to cyclobutanes is the [2+2] cycloaddition of alkenes; photochemical activation enables the reaction, whereas thermal [2+2] cycloadditions are symmetry-forbidden without special conditions. Reduction of cyclobutene gives cyclobutane. Ring-opening reactions can occur under harsh conditions, yielding open-chain dienes or alkanes. Substituted cyclobutanes may show cis/trans relationships for 1,2-disubstituted rings.

Occurrence and uses: Cyclobutane rings feature in a range of synthetic building blocks, natural products, and pharmaceutical scaffolds. They provide conformational rigidity and three-dimensional diversity useful in medicinal chemistry and materials science. Safety and handling: Cyclobutane and many of its derivatives are flammable; standard chemical hygiene practices apply.