Survey of the Natural Sciences - Organic Chemistry
What the organic chemistry section tests
The OAT organic chemistry section tests structure and bonding, functional groups, nomenclature, stereochemistry, conformations, substitution and elimination, addition reactions, aromaticity, carbonyl chemistry, and IR/NMR/mass spectrometry. You need to connect a structure to its properties and to a plausible mechanism.
Core rules
- Hybridization: sp3 = tetrahedral, sp2 = trigonal planar, sp = linear. Aromatic rings are sp2 and planar with 4n+2 π electrons.
- Stereochemistry: assign priorities by atomic number; if the lowest priority points away, clockwise = R. A wedge/dash inversion means reverse the result.
- SN1/SN2: SN2 is concerted, backside attack, favored by a strong nucleophile, methyl/primary substrate, and polar aprotic solvent. SN1 goes through a carbocation, favored by tertiary substrate and polar protic solvent.
- E1/E2: E2 is concerted and needs anti-periplanar geometry; a strong bulky base favors E2.
- Spectroscopy: IR C=O near 1700 cm−1; NMR splitting = n+1 from neighboring equivalent protons.
Worked example
A chiral carbon bears Cl, OH, CH3, and H. Priorities: Cl (1, atomic number 17) > OH (2, O=8) > CH3 (3, C=6) > H (4). With H pointing away and 1→2→3 clockwise, the configuration is R. If H is not pointing away, reverse the result.
Traps
- Assigning R/S without putting H away.
- Treating a primary alkyl halide as SN1-favored.
- Forgetting that OH is an alcohol, not a carboxylic acid.
- Reading an NMR integration as splitting.
- Assuming all planar rings are aromatic; check the π-electron count.