An alkyl chloride produces a single alkene on reaction with sodium ethoxide and ethanol. The alkene further undergoes hydrogenation to yield 2-methylbutane. Identify the alkyl chloride from amongst the following. (a) \(\mathrm{ClCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{ClCH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{C}(\mathrm{Cl})\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{3}\)

The E2 mechanism stands for bimolecular elimination and is a fundamental process in organic chemistry. During this reaction, a base removes a proton (a hydrogen atom) from the molecule, while concurrently a leaving group, such as a halide, departs, resulting in the formation of an alkene.

Let's understand this through a basic analogy: Imagine a dance floor (the molecule) with dancers (atoms or groups of atoms). One dancer decides to leave (the leaving group), but only when another dancer (the base) simultaneously takes a step back (removes a hydrogen). This coordinated movement results in new dancing space (a double bond) on the floor. The 'bi' in E2 signifies that both the base and the molecule must participate in this dance move at the same time.

Characteristics of E2 Reactions

• Concerted: Both bond-breaking and bond-making happen in one single, concerted step.
• Regioselectivity: The base specifically removes a proton that allows for the formation of the most stable alkene.
• Stereospecificity: The geometry of the product is often dictated by the orientation of the groups in the starting material.
• Rate of Reaction: The reaction rate is dependent on both the concentration of the base and the substrate (the reactant alkyl halide).

In relation to the exercise given, sodium ethoxide acts as the base, removing a hydrogen atom adjacent to a carbon bearing a chlorine atom, allowing for the formation of an alkene through an E2 elimination reaction.

Alkyl chlorides, also known as alkyl halides, are organic compounds containing a chlorine atom bonded to an alkyl group. In the context of elimination reactions, they are interesting because the chlorine atom can serve as a good leaving group.

Imagine you're packing bags for a trip (the reaction). If the bag (alkyl chloride) is too heavy or packed inefficiently (sterically hindered), it's cumbersome to carry it along (react). But if it's just right, you can leave for your trip smoothly (reaction proceeds effectively).

Properties of Alkyl Chlorides

• Reactivity: The reactivity of alkyl chlorides in elimination reactions depends greatly on the type of carbon they are attached to (primary, secondary, or tertiary).
• Leaving group ability: A chlorine atom is a relatively good leaving group, which helps facilitate E2 and other elimination reactions.
• Structural influence: The structure of the alkyl chloride influences the stability of the transition state and consequently, the ease of elimination.

In the textbook exercise, the alkyl chloride options represent different types of carbons to which the chlorine is attached, thereby impacting the likelihood of forming the most stable alkene through elimination.

Alkene hydrogenation is a reaction where hydrogen is added across the double bond of an alkene, resulting in a saturated alkane. It can be likened to repairing a broken zipper on a jacket. When the zipper (double bond) is split open, it can be fixed (hydrogenated) by adding the missing teeth (hydrogen atoms).

For a successful hydrogenation, you need a catalyst, such as palladium, platinum, or nickel, which serves as a surface where the alkene and hydrogen interact. This catalyst is essential for facilitating the reaction just like a repair tool is for fixing the zipper.

Stages of Hydrogenation

• Adsorption: The alkene and hydrogen gases bind to the surface of the catalyst.
• Hydrogenation: Hydrogen atoms are added to the carbons of the double bond, closing it to make a single bond.
• Desorption: The now-saturated alkane detaches from the catalyst, completing the process.

In the given exercise, the correct alkene derived from an E2 elimination must become 2-methylbutane when hydrogenated. This transformation from an unsaturated to a saturated molecule is significant in many industries, including food production and petrochemical processing.