OC-02 — Complete Cheat Sheet (Exam Day Ready)
Hydrocarbon Formulas
| Class | Formula | Example | SMILES |
|---|---|---|---|
| Alkane | Cₙₙ₊_{2} | Ethane | CC |
| Alkene | Cₙₙ | Propene | CC=C |
| Alkyne | Cₙₙ₋_{2} | But-2-yne | CC#CC |
Butane Conformations (Decreasing Stability)
| Conformation | Dihedral | Energy Above Anti | Mnemonic Letter |
|---|---|---|---|
| Anti | 180° | 0 kJ/mol | A |
| Gauche | 60° | ~3.8 kJ/mol | G |
| Eclipsed | 120° | ~16 kJ/mol | E |
| Fully eclipsed | 0° | ~19 kJ/mol | F |
Mnemonic: "A Gentle Evening Falls"
Free Radical Halogenation Summary
Initiation: $X_{2}$ --[UV/]--> 2X•
Propagation: R–H + X• → R• + HX then R• + $X_{2}$ → R–X + X•
Termination: R• + R• → R–R
Selectivity: 3° > 2° > 1° H | Halogen selectivity: >> >
Addition Reactions of Alkenes
| Reagent | Condition | Rule | Product from Propene |
|---|---|---|---|
| HBr | No peroxide | Markovnikov | 2-bromopropane CC(Br)C |
| HBr | + ROOR (peroxide) | Anti-Markovnikov | 1-bromopropane CCCBr |
| O | Dil. H_{2}$$SO_{4} | Markovnikov | Propan-2-ol |
| Anti-addition | Vicinal dihalide | ||
| /Zn/O | Reductive | C=C cleavage | Aldehydes + Ketones |
KEY RULE: Anti-Markovnikov = ONLY HBr + peroxide. HCl and HI do NOT work.
Alkyne Reduction
| Reagent | Addition Type | Product Geometry |
|---|---|---|
| / Lindlar's (Pd/CaC + Pb(OAc)_{2} + quinoline) | Syn | cis-alkene (Z) |
| Na / liq. (Birch-type) | Anti | trans-alkene (E) |
| / Pd–C (excess) | Syn → complete | Alkane |
Mnemonic: "Lindlar = cis (L for 'sis'). Na/ = trans (N for opposite)"
Alkyne Acidity
| Hybridization | % s-character | Example | pKa | Reaction with NaN? |
|---|---|---|---|---|
| sp | 50% | Ethyne C#C | ~25 | YES → acetylide |
| 33.3% | Ethene C=C | ~44 | NO | |
| 25% | Ethane CC | ~50 | NO |
KEY RULE: More s-character = More electronegative carbon = More acidic C–H
Top 3 NEET Trap Answers
- "Anti-Markovnikov works with HCl and HBr" → WRONG. Only HBr.
- "Lindlar's gives trans-alkene" → WRONG. Lindlar's = cis. Na/ = trans.
- "Gauche is least stable butane conformation" → WRONG. Fully eclipsed (0°) is least stable.