Bicyclo221hept2ene

Bicyclo[2.2.1]hept-2-ene, commonly called norbornene, is a highly strained bicyclic hydrocarbon with seven carbons. It consists of a cyclopentane ring fused to a cyclopropane via shared bridgehead carbons, connected by three carbon bridges of lengths 2, 2, and 1. The molecule carries a single internal double bond between C-2 and C-3, giving the formula C7H8. The small ring system imposes significant ring strain, which elevates the reactivity of the double bond relative to unstrained alkenes.

Synthesis and preparation: Norbornene can be prepared directly by a Diels–Alder reaction between cyclopentadiene and ethylene; this classical route provides the parent compound. It can also be obtained by dehydrogenation of norbornane derivatives or via rearrangements of related bicyclic systems.

Reactivity and applications: The strained alkene behaves as a reactive dienophile in cycloadditions and as a key monomer in ring-opening metathesis polymerization (ROMP), yielding polynorbornene-like polymers with attractive mechanical properties. In organic synthesis, norbornene derivatives are employed to control stereochemistry and to introduce rigid bicyclic motifs. Substituted norbornenes exhibit endo/exo stereochemical preferences in Diels-Alder reactions.

Safety and handling: Norbornene is a volatile, flammable hydrocarbon. It can induce irritation to skin and eyes and should be handled in a well-ventilated hood with appropriate personal protective equipment. It is stored away from oxidizers and heat.