25 Key Terms — OC-02 Glossary
1. Alkane — Saturated hydrocarbon with formula Cₙₙ₊_{2}; all C–C and C–H single bonds; hybridized carbons.
2. Alkene — Unsaturated hydrocarbon with formula Cₙₙ; contains at least one C=C double bond; hybridized at the double bond carbons.
3. Alkyne — Unsaturated hydrocarbon with formula Cₙₙ₋_{2}; contains at least one C≡C triple bond; sp hybridized at the triple bond carbons.
4. Conformation — A three-dimensional arrangement of atoms in a molecule resulting from rotation around a single bond; not a structural isomer (same connectivity).
5. Newman Projection — A diagram showing the view along a C–C bond: the front carbon is a dot, the back carbon is a circle, and substituents are shown as lines.
6. Dihedral Angle (torsion angle) — The angle between two planes defined by substituents on adjacent carbons when viewed in Newman projection.
7. Torsional Strain — Destabilizing energy arising from eclipsing of bonding orbitals on adjacent carbons (most important in ethane).
8. Steric Strain — Destabilizing energy from repulsion between non-bonded atoms or groups that are forced into close spatial proximity.
9. Staggered Conformation — A conformation in which bonds on adjacent carbons are offset (dihedral angle ≠ 0°, 120°, 240°); most stable for ethane at 60° dihedral.
10. Eclipsed Conformation — A conformation in which bonds on adjacent carbons are aligned (dihedral angles 0°, 120°, 240°); less stable due to torsional/steric strain.
11. Anti Conformation — The staggered conformation with a dihedral angle of 180° (e.g., anti-butane with the two methyl groups maximally separated).
12. Gauche Conformation — A staggered conformation with a dihedral angle of 60° or 300°; the two methyl groups in butane are close but not eclipsing.
13. Free Radical Halogenation — A substitution reaction of alkanes with (hν or ) proceeding via initiation, propagation, and termination steps with radical intermediates.
14. Initiation — The first step of a radical chain reaction; homolysis of by UV/heat to give two X• radicals.
15. Propagation — Chain-carrying steps in free radical halogenation: (i) R–H + X• → R• + HX; (ii) R• + → R–X + X•.
16. Termination — Steps that destroy radicals and end the chain: R• + R•, R• + X•, or X• + X• combinations.
17. Markovnikov's Rule — In electrophilic addition of HX to an unsymmetrical alkene, H adds to the carbon with more H atoms (equivalent: the more stable carbocation intermediate is formed).
18. Kharasch Effect (Anti-Markovnikov Addition) — Addition of HBr to an alkene in the presence of organic peroxide by a free radical mechanism; Br adds to the less substituted carbon; ONLY works with HBr.
19. Electrophilic Addition — Reaction of an alkene with an electrophile; proceeds via carbocation intermediate; follows Markovnikov's rule for HX addition.
20. Ozonolysis — Cleavage of C=C double bonds by ozone () to give an ozonide intermediate, which is then decomposed to carbonyl compounds (aldehydes/ketones with reductive workup Zn/O, or carboxylic acids with oxidative workup H_{2}$$O_{2}).
21. Lindlar's Catalyst — Partially deactivated hydrogenation catalyst: Pd deposited on CaC, poisoned with Pb(OAc)_{2} and quinoline. Reduces alkynes to cis-alkenes (syn-addition).
22. Dissolving Metal Reduction (Birch for alkynes) — Reduction of alkynes with Na (or Li) in liquid ; proceeds via radical anion mechanism; gives trans-alkene (anti-addition).
23. syn-Addition — Addition of two groups to the SAME face of a double/triple bond; example: Lindlar's addition to alkynes gives cis-alkene.
24. anti-Addition — Addition of two groups to OPPOSITE faces of a double/triple bond; examples: addition to alkenes (via bromonium ion), Na/ reduction of alkynes.
25. Acetylide Ion — The conjugate base of a terminal alkyne (RC≡); formed by treating terminal alkyne with NaN (or n-BuLi); a powerful carbon nucleophile used in synthesis (e.g., acetylide alkylation with alkyl halides).