Govt. Exams
Entrance Exams
The initially formed secondary carbocation rearranges via methyl shift to form a more stable tertiary carbocation, producing 2-methylbut-2-ene as major product.
Formaldehyde is the only aldehyde without an α-hydrogen, so it undergoes the Cannizzaro reaction where it acts as both oxidizing and reducing agent, forming formate and methanol.
Malonic acid derivatives (with two electron-withdrawing groups) undergo decarboxylation through a cyclic transition state mechanism, facilitated by the stabilization of the resulting carbanion by the remaining electron-withdrawing group.
2-bromobutane (CH3CHBrCH2CH3) has a carbon with four different groups attached, making it chiral. The bromine-bearing carbon is a stereocenter.
No C=O in IR rules out ketone/aldehyde. The signals at δ 3.8 (OCH2) and δ 4.7 suggest acetal carbons (characteristic of dioxolane ring). 2,2-dimethyl-1,3-dioxolane fits C5H10O2 with protected diol functionality.
Hydroboration occurs through a concerted mechanism involving a four-membered ring transition state, resulting in syn-addition of BH across the double bond.
The singlet at δ 3.3 ppm suggests the OH is on a quaternary carbon (no neighboring H, hence no coupling). 2,3-dimethyl-2-butanol fits: the OH is on a quaternary carbon, explaining the singlet and broad O-H in IR.
β-Ketoacids (RCOCH2COOH) undergo easy decarboxylation through a six-membered transition state, producing ketones. This is more facile than decarboxylation of regular carboxylic acids.
Iodoform test requires CH3CO- group. Pentan-2-ol (CH3CH2CH(OH)CH3) can be oxidized to CH3COCH2CH3 which contains the required methyl ketone group.
F-C alkylation proceeds via carbocation formation. Tertiary carbocations are most stable, followed by secondary, then primary. Reactivity: Tertiary > Secondary > Primary.
