Mind Map For Hydrocarbons: Alkenes | Class 11, JEE & NEET - Download from here

The general molecular formula of alkenes is CₙH₂ₙ, where n ≥ 2. Alkenes contain one carbon–carbon double bond (C=C), which makes them unsaturated hydrocarbons. The simplest alkene is ethene (C₂H₄), commonly called ethylene. This formula distinguishes alkenes from alkanes (CₙH₂ₙ₊₂) and alkynes (CₙH₂ₙ₋₂).

For JEE Main, the highest-priority alkene reactions are Markovnikov addition of HX, ozonolysis (product identification), anti-Markovnikov addition with HBr/peroxides, and oxidation with KMnO₄. Questions on geometrical isomerism (cis-trans) and heat of hydrogenation also appear regularly. Mastering these seven topics covers approximately 80% of alkene-based JEE Main questions from the past five years.

Markovnikov's rule states that in HX addition to an unsymmetrical alkene, H adds to the carbon with more hydrogens. For propene (CH₃–CH=CH₂) + HBr: H adds to CH₂ (more H's), Br adds to CH (more substituted), giving 2-bromopropane — not 1-bromopropane. The rule is explained by carbocation stability: the secondary carbocation at C-2 is more stable than the primary at C-1.

The peroxide effect (Kharasch effect) is the anti-Markovnikov addition of HBr to alkenes in the presence of organic peroxides (ROOR). Peroxides initiate a free-radical chain mechanism. The bromine radical adds to the less substituted carbon (forming the more stable secondary radical), giving the product opposite to Markovnikov's rule. Crucially, this reversal applies only to HBr — not HCl or HI.

eSaral provides three downloadable mind maps for alkenes: Mind Map 1 covers structure and nomenclature, Mind Map 2 covers isomerism (chain, position, and geometric), and Mind Map 3 covers all major reactions including addition, oxidation, and polymerisation. Together they cover the complete Class 11 Hydrocarbons – Alkenes syllabus for CBSE, JEE, and NEET.