Write equations for the following: (a) an addition reaction...

Write equations for the following: (a) an addition reaction between $\mathrm{H}_{2} \mathrm{O}$ and 3 -hexene $\left(\mathrm{H}^{+}\right.$ is a catalyst $) ;$ (b) an elimination reaction between 2 -bromopropane and hot potassium ethoxide, $\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OK}(\mathrm{KBr}$ and ethanol are also products $) ;$ (c) a lightinduced substitution reaction between $\mathrm{Cl}_{2}$ and ethane to form 1,1 -dichloroethane.

Key Concepts

Elimination Reaction (E2 Mechanism)

An elimination reaction involves the removal of a leaving group and a hydrogen atom from adjacent carbon atoms, resulting in the formation of a double bond. In the E2 mechanism, which is bimolecular and occurs in a single concerted step, a strong base (such as potassium ethoxide) removes a proton while the leaving group (such as bromide) departs simultaneously, producing an alkene along with byproducts such as an alkoxide salt and, after proton transfer, an alcohol.

Free Radical Substitution Reaction

This mechanism involves the formation of reactive radical species, typically initiated by light (hv), which cause the substitution of atoms in saturated hydrocarbons. Under irradiation, a halogen molecule (like Cl2) splits to form two chlorine radicals that can abstract a hydrogen atom from an alkane, generating an alkyl radical. This alkyl radical then reacts with another molecule of the halogen to form a substituted product, completing the chain reaction.

Electrophilic Addition Reaction

This reaction involves the addition of an electrophile and a nucleophile across a carbon–carbon multiple bond, typically seen with alkenes. In acid-catalyzed hydration of an alkene, the double bond acts as a nucleophile, attacking a proton (from the acid catalyst) to form a carbocation intermediate, which is then attacked by a water molecule, ultimately yielding an alcohol after deprotonation.

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