Organic Chemistry
Organic chemistry in JAM CY rewards mechanism-level reasoning: bonding and hybridization, stereochemistry, reaction intermediates, functional-group transformations, aromaticity, and pericyclic rules. You should be able to push electrons, assign configuration, and choose between competing pathways.
Core rules
- Nucleophilic substitution: SN2 is concerted, backside attack, second order, and favoured by methyl/primary substrates, strong nucleophiles, and polar aprotic solvents. SN1 is stepwise via carbocation, first order, and favoured by tertiary/benzylic substrates and polar protic solvents.
- Elimination: E2 needs an anti-periplanar β-H and is favoured by strong bulky bases; E1 shares a carbocation intermediate with SN1.
- Aromaticity: cyclic, planar, fully conjugated, and 4n + 2 π electrons. Count lone pairs only if they reside in a p orbital that participates in the ring.
- Carbonyl chemistry: nucleophiles add to the carbonyl carbon; leaving-group ability follows I− > Br− > Cl− > F− for acyl substitution; acid catalysis activates the carbonyl.
- Stereochemistry: assign R/S by CIP priority; for E/Z, compare priorities at each alkene carbon.
Worked example
Rank 1-bromobutane, 2-bromobutane, and 2-bromo-2-methylpropane for SN2 reactivity. SN2 rate is dominated by steric hindrance at the reacting carbon. 1-bromobutane is primary and fastest. 2-bromobutane is secondary, so slower. 2-bromo-2-methylpropane is tertiary and essentially unreactive by SN2; it proceeds by SN1 or E1 instead. Order: 1-bromobutane > 2-bromobutane > 2-bromo-2-methylpropane.
Traps
Reversing SN2 stereochemistry when the nucleophile is not the highest-priority group; drawing E2 without anti-periplanar geometry; counting an sp³ lone pair as part of an aromatic π system; forgetting that tertiary halides do not undergo SN2; and assigning R/S from a 2D drawing without viewing the lowest-priority group away.