NEET Hydrocarbons: Alkanes, Alkenes, Alkynes and Aromatic Hydrocarbons

Cover nomenclature, isomerism, general preparation/property patterns and ethane conformations using Sawhorse/Newman representations as explicitly listed. For halogenation, teach free-radical substitution at the level needed to understand initiation, propagation and termination, without importing advanced radical kinetics.

A representative chlorination equation is:

CH4 + Cl2 --hν--> CH3Cl + HCl

Further substitution can occur with excess chlorine; therefore do not imply a single monochloro product is guaranteed under all conditions.

The central reactive feature is the pi bond. Electrophilic addition should be reasoned from electron density and reagent conditions.

• Hydrogenation: CH2=CH2 + H2 --Ni/Pt/Pd--> CH3-CH3.
• Bromination: CH2=CH2 + Br2 -> BrCH2-CH2Br.
• Hydration under acid catalysis gives an alcohol; orientation follows the verified substrate/reagent context.
• Addition of hydrogen halides: Markovnikov orientation is the standard relationship for unsymmetrical alkenes under normal ionic conditions.
• Peroxide effect: within the current NCERT/NEET scope, the anti-Markovnikov peroxide effect is associated with HBr, not HCl or HI. Example:

CH3-CH=CH2 + HBr --peroxide--> CH3-CH2-CH2Br.

Ozonolysis should be used as a structural-diagnosis tool: cleavage products reveal the original double-bond substitution pattern. Do not overstate work-up variants beyond current scope.

Polymerisation is explicitly named in Unit 15, but this does not make the separate /polymers route a current standalone syllabus unit.

Teach terminal-alkyne acidity as a relative property related to hybridisation, at NEET depth. Cover addition of H2, X2, H2O and HX only with correct conditions. For hydration, avoid presenting a single generic product without specifying substrate/conditions because enol formation and tautomerisation determine the observed carbonyl product.

Example hydrogenation:

HC≡CH + 2H2 --Ni/Pt/Pd--> CH3-CH3.

Benzene should be treated through structure, aromatic stabilisation and electrophilic substitution. Current scope explicitly includes halogenation, nitration, Friedel-Crafts alkylation/acylation and directive influence in monosubstituted benzene.

Representative nitration:

C6H6 + HNO3 --conc. H2SO4--> C6H5NO2 + H2O.

Representative bromination:

C6H6 + Br2 --FeBr3--> C6H5Br + HBr.

Directive effects should be tied to substituent electron donation/withdrawal and resonance/inductive effects; do not turn them into an unqualified memorisation chart detached from reaction conditions.

Hydrocarbon Reaction Selector separating radical substitution, electrophilic addition and electrophilic aromatic substitution so students diagnose the reaction family before predicting products.

Original NEET-style reasoning item: Propene reacts separately with HBr (no peroxide) and HBr in the presence of peroxide. Should both reactions be predicted with the same orientation?

Reasoning: No. The peroxide condition changes the relevant pathway for HBr in the current textbook scope.

Original Rank Sarthi reasoning item. It is not a past-year question and carries no exam provenance.