Answer to Question #126637 in Organic Chemistry for Nirupama Behera

Question

Electrocyclic pericyclic reaction of 1chloro bromo bycyclic hexane

Answer 1

 Electrocyclic Reactions An electrocyclic reaction is a reversible reaction that involves ring closure of a conjugated polyene to a cycloalkene, or ring opening of a cycloalkene to a conjugated polyene. For example, ring closure of 1,3,5-hexatriene forms 1,3-cyclohexadiene, a product with one more σ bond and one fewer π bond than the reactant. Ring opening of cyclobutene forms 1,3-butadiene, a product with one fewer σ bond and one more π bond than the reactant. Ring-closing reaction Ring-opening reaction ∆ 1,3,5-hexatriene 1,3-cyclohexadiene new σ bond ∆ cyclobutene 1,3-butadiene To draw the product in each reaction, use curved arrows and begin at a π bond. Move the π electrons to an adjacent carbon–carbon bond and continue in a cyclic fashion. In a ring-forming reaction, this process forms a new σ bond that now joins the ends of the conjugated polyene. In a ring-opening reaction, this process breaks a σ bond to form a conjugated polyene with one more π bond. Whether the reactant or product predominates at equilibrium depends on the ring size of the cyclic compound. Generally, a six-membered ring is favored over an acyclic triene at equilibrium. In contrast, an acyclic diene is favored over a strained four-membered ring.