Match the following: List I (Reactants) 1\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{alc} . \mathrm{KOH}\) 2\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3}+\) alc. \(\mathrm{KOH}\) 3\. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CBr}+\) alc. \(\mathrm{KOH}\) List II (Products) A. cis-but-2-ene B. trans-but-2-ene C. but-1-ene D. 2-methylprop-1-ene The correct matching is \(1 \quad 2 \quad 3\) \(\begin{array}{lll}\text { (a) } \mathrm{C} & \mathrm{B} & \mathrm{D}\end{array}\) (b) \(\mathrm{C} \quad \mathrm{A} \quad \mathrm{D}\) (c) \(\mathrm{C} \quad \mathrm{D} \quad \mathrm{A}\) \(\begin{array}{lll}\text { (d) B } & \text { A } & \text { C }\end{array}\)

When an alkyl halide encounters alkaline potassium hydroxide (KOH), especially in alcoholic solution, it commonly undergoes an elimination reaction. During this process, a halogen atom is removed from the alkyl halide along with a hydrogen atom from an adjacent carbon.

For example, when butyl bromide (CH_3CH_2CH_2CH_2Br) reacts with alcoholic KOH, the bromide (Br) and a hydrogen atom from an adjacent carbon are removed, resulting in the formation of but-1-ene.

This reaction is favored by specific conditions, such as the use of alcoholic KOH and elevated temperatures, which steer the reaction towards elimination rather than substitution. The alkene formed is often more substituted due to the stability provided by the additional alkyl groups, which is guided by Zaitsev's rule.

Formation of alkenes from alkyl halides is a prime example of elimination reactions in organic chemistry. The process entails deprotonation of a bonded hydrogen and simultaneous removal of the halide, culminating in the creation of a double bond between two carbon atoms.

For instance, the elimination from butyl bromide and alcoholic KOH leads to but-1-ene, showcasing a double bond between the first and second carbon atoms. Reflecting on the given problem, the result is the generation of various alkenes such as but-1-ene, trans-but-2-ene, and 2-methylprop-1-ene, depending on the specific structure of the starting alkyl halide.

These structural variations affect not just the chemical properties but also the physical characteristics of the alkenes formed, influencing their reactivity and usefulness in further chemical processes or as final products in industrial applications.

Zaitsev's Rule is a fundamental principle dictating the outcome of many elimination reactions in organic chemistry. Named after the Russian chemist Alexander Zaitsev, it states that in an elimination reaction, the most substituted alkene—typically the one with the greatest number of alkyl groups attached to the carbon atoms forming the double bond—will be the major product.

This is due to steric and electronic factors that favor the formation of the more substituted, and thus more stable, alkene. For example, when 2-bromobutane reacts with alcoholic KOH, Zaitsev's Rule predicts the major product will be trans-but-2-ene instead of the less substituted but-1-ene.

This rule is exceptionally useful as it provides guidance to predict the major product of elimination reactions, which is crucial for students and chemists to understand reaction outcomes and for planning syntheses.