Alkynes — Prelims Strategy

Prelims Strategy

To excel in NEET questions on alkynes, a systematic approach is essential. Firstly, thoroughly understand the basic structure, $sp$ hybridization, and nomenclature. Pay close attention to the distinction between terminal and internal alkynes, as this is fundamental to many reactions and tests.

For reaction-based questions, create a mental or physical 'reagent-product map'. For instance, associate 'Lindlar's catalyst' with 'cis-alkene' and 'Na/liq. $NH_3$' with 'trans-alkene'. Similarly, remember that $HgSO_4/H_2SO_4$ means 'hydration to aldehyde/ketone'.

When dealing with hydrohalogenation, always consider Markovnikov's rule and its anti-Markovnikov variant (HBr with peroxides). Remember that for alkynes, two equivalents of reagent can add. For distinguishing tests, memorize that Tollens' reagent and ammoniacal cuprous chloride are specific for terminal alkynes (due to their acidic hydrogen), while bromine water and Baeyer's reagent are general tests for unsaturation (react with both alkenes and alkynes).

Practice predicting products for various alkynes (ethyne, terminal alkynes, internal alkynes) under different reaction conditions. Pay attention to the number of equivalents of reagents mentioned, as this dictates whether one or two additions occur.

Finally, review the relative acidity of hydrocarbons (alkynes > alkenes > alkanes) and the reason behind it (s-character).