Consider the heterolytic cleavage of the C - Br bond in the following compounds: (P) 3-Bromocyclopropene (Q) Benzyl bromide (R) Bromoethane (S) 5-Bromo-1,3-cyclopentadiene The correct decreasing order of their heterolytic carbon-bromine bond dissociation enthalpies is:

Step-by-step solution

Heterolytic cleavage of the C - Br bond produces a carbocation and a bromide ion ( R - Br R ^ + Br ^ ). The heterolytic bond dissociation enthalpy is inversely proportional to the stability of the resulting carbocation. A more stable carbocation requires less energy to be formed. The carbocations formed are: (P) Cyclopropenyl cation: It has 2 electrons in a cyclic, planar, conjugated system. It is aromatic and exceptionally stable. (Q) Benzyl cation: It is stabilized by resonance with the benzene ring. (R) Ethyl ca