Organic Chemistry: Mechanisms and Stereochemistry
The high-yield map
Organic questions are pattern recognition. Know hybridization and geometry, resonance delocalization, aromaticity (Hückel: cyclic, planar, fully conjugated, 4n+2 π electrons), and acid–base trends driven by induction, resonance, hybridization, and size. Stereochemistry is guaranteed: chiral centers, R/S assignment, E/Z, enantiomers versus diastereomers, meso compounds, and the stereochemical outcome of each mechanism (SN2 inverts; SN1 racemizes).
Then the reaction families: SN1/SN2/E1/E2 (substrate, nucleophile strength, base strength, leaving group, solvent), alkene additions (Markovnikov vs anti-Markovnikov, syn vs anti), oxidation and reduction, and carbonyl chemistry - nucleophilic addition, hemiacetals and acetals as protecting groups, imines, aldol condensation, esterification and hydrolysis. Spectroscopy appears too: IR functional-group stretches, ¹H NMR shift, integration, and n+1 splitting, and mass spec fragmentation.
Traps
- Calling a ring aromatic because it looks conjugated, without counting π electrons.
- Assuming a strong base always means E2 - heat and bulky bases favor elimination, but a strong nucleophile on a primary halide still substitutes.
- Forgetting solvent effects: polar protic stabilizes carbocations (SN1/E1), polar aprotic favors SN2.
- Ignoring stereochemistry when the stem asks for the product.
- Misreading splitting: a proton with three equivalent neighbors gives a quartet, not a triplet.
Rule of thumb
Leaving-group ability tracks conjugate-base stability, so I⁻ > Br⁻ > Cl⁻ > F⁻. Weak, stable conjugate bases leave readily; strong, unstable ones do not.
Worked example
2-bromobutane with NaCN in DMSO: cyanide is a strong nucleophile, DMSO is polar aprotic, and the substrate is secondary - SN2 dominates, giving 2-methylbutanenitrile with inverted configuration at C2.