Govt. Exams
Entrance Exams
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.
SN1 is a unimolecular reaction with rate = k[R-X]. It is first-order with respect to alkyl halide only, independent of nucleophile concentration.
Cannizzaro reaction occurs with aldehydes lacking α-hydrogens. Acetaldehyde has α-hydrogens, so it undergoes aldol condensation instead of Cannizzaro reaction.
Dehydration follows Zaitsev's rule, producing the most substituted (stable) alkene. 2-methylbut-2-ene is the major product with the double bond at the tertiary position.
Nitration involves formation of NO2+ (nitronium ion) from HNO3 in presence of H2SO4. NO2+ acts as the electrophile in electrophilic aromatic substitution.
Basic hydrolysis of alkyl halides follows SN2 mechanism (bimolecular nucleophilic substitution) with OH- as nucleophile, especially for primary halides.
PCC oxidizes primary alcohols to aldehydes without further oxidation to carboxylic acids. KMnO4 and Na2Cr2O7 further oxidize aldehydes to carboxylic acids.
Aldol condensation requires an α-hydrogen. Acetaldehyde has α-hydrogens and undergoes aldol condensation. Benzaldehyde and formaldehyde lack α-hydrogens.
Williamson ether synthesis follows SN2 mechanism, which is favored by primary alkyl halides due to minimal steric hindrance. Reactivity: Primary > Secondary > Tertiary.
