Alkanes — Prelims Strategy

Prelims Strategy

For NEET questions on alkanes, a systematic approach is key.

1
Nomenclature: — Practice IUPAC naming extensively. Always identify the longest continuous carbon chain, number it to give substituents the lowest possible locants, and list substituents alphabetically. Be mindful of common names for simple branched alkanes (iso-, neo-).
2
Isomerism: — Understand the concept of chain isomerism. For physical properties, remember the rule: increased branching leads to decreased boiling point due to reduced surface area for van der Waals forces.
3
Preparation Reactions: — Memorize the specific reagents and conditions for each method. For instance, Wurtz reaction uses Na/dry ether and is best for symmetrical alkanes. Decarboxylation uses soda lime ($NaOH/CaO$). Hydrogenation uses $H_2$ with Ni/Pd/Pt. Focus on the products formed and any limitations (e.g., Wurtz for unsymmetrical alkanes).
4
Chemical Reactions (especially Halogenation): — Understand the free radical mechanism (initiation, propagation, termination). Crucially, remember the reactivity order of hydrogen atoms ($3^circ > 2^circ > 1^circ$) and halogens ($F_2 > Cl_2 > Br_2 > I_2$). This helps predict major products in monohalogenation.
5
Conceptual Clarity: — Alkanes are saturated, so they don't undergo addition reactions. They are nonpolar and insoluble in water. Use these fundamental principles to eliminate incorrect options.
6
Practice MCQs: — Solve a variety of MCQs, including those that test multiple concepts simultaneously. Pay attention to trap options, which often exploit common misconceptions like confusing reaction types or reagents.