Common Errors Analysis

Error 1: Confusing anti-Markovnikov HX scope

WRONG: "HCl or HI with peroxide also gives anti-Markovnikov product"
CORRECT: ONLY HBr + peroxide gives anti-Markovnikov addition. HCl fails (endothermic radical step). HI fails (premature chain termination). This is the single most tested trap in NEET.

Error 2: Inverting Lindlar vs Na/ $NH_{3}$ products

WRONG: "Lindlar's catalyst gives trans-alkene"
CORRECT: Lindlar's = cis-alkene (syn-addition). Na/liq. $NH_{3}$ = trans-alkene (anti-addition). Use mnemonic: "Lindlar = cis (L for 'sis' = same side). Na = N for opposite."

Error 3: Confusing least stable butane conformation

WRONG: "The gauche conformation is least stable in butane"
CORRECT: Fully eclipsed (0° dihedral, $CH_{3}$ eclipsing $CH_{3}$ ) is least stable. Gauche is only ~3.8 kJ/mol above anti.

Error 4: Confusing termination with propagation

WRONG: "R–H + X• → R• + HX is a termination step"
CORRECT: R–H + X• → R• + HX is the FIRST PROPAGATION step. Termination involves combination of two radicals (radical + radical → stable molecule).

Error 5: Misidentifying ozonolysis products

WRONG: "Ozonolysis always gives carboxylic acids"
CORRECT: Reductive ozonolysis (Zn/ $H_{2}O$ ) gives aldehydes (if –CH=) or ketones (if –CR=). Oxidative workup ( $H_{2}O$ _{2}) gives carboxylic acids from aldehydes.

Error 6: Incorrect acidity ordering

WRONG: "Alkenes are more acidic than alkynes because they are more reactive"
CORRECT: Terminal alkynes are MORE acidic (pKa ~25) than alkenes (pKa ~44) due to 50% s-character in sp C–H bonds. Reactivity ≠ acidity.

Error 7: Claiming Lindlar's is a homogeneous catalyst

WRONG: "Lindlar's catalyst dissolves in the reaction mixture"
CORRECT: Lindlar's is a HETEROGENEOUS catalyst (solid Pd on $CaCO_{3}$ support). The reaction occurs on the surface of the solid catalyst.

Error 8: Applying Markovnikov to radical conditions

WRONG: "All HX additions to alkenes follow Markovnikov regardless of conditions"
CORRECT: Without peroxide → Markovnikov (ionic). With peroxide + HBr → anti-Markovnikov (radical). Conditions determine mechanism and product.