Govt Exams
FeBr3 is a Lewis acid that polarizes Br2, generating Br+ (bromonium ion) which acts as the electrophile in electrophilic aromatic substitution of benzene.
Friedel-Crafts alkylation using CH3Cl with AlCl3 as Lewis acid catalyst converts benzene to toluene. This is the standard industrial method for alkylbenzene synthesis.
Esterification (Fischer esterification) requires acid catalyst (H2SO4 or HCl) which protonates the carbonyl oxygen, increasing electrophilicity and facilitating nucleophilic attack by alcohol.
β-Ketoacids (RCOCH2COOH) undergo easy decarboxylation through a six-membered transition state, producing ketones. This is more facile than decarboxylation of regular carboxylic acids.
RMgX + CO2 → RMgX-O2C- → RCOO- MgX+ → RCOOH (after acidification). This is a classic method for carboxylic acid synthesis.
In staggered conformation, bonds are maximally separated reducing electron-electron repulsion and torsional strain. Staggered is most stable with ~12 kJ/mol lower energy than eclipsed.
Iodoform test requires CH3CO- group. Pentan-2-ol (CH3CH2CH(OH)CH3) can be oxidized to CH3COCH2CH3 which contains the required methyl ketone group.
Formic acid is most acidic (Ka = 1.8×10-4) due to favorable +I effect of hydrogen. Acidity decreases with increasing alkyl chain length due to +I effect: Formic > Acetic > Propionic.
F-C alkylation proceeds via carbocation formation. Tertiary carbocations are most stable, followed by secondary, then primary. Reactivity: Tertiary > Secondary > Primary.
SN1 is a unimolecular reaction with rate = k[R-X]. It is first-order with respect to alkyl halide only, independent of nucleophile concentration.