Cue Column | Notes Column

What are the 3 classes of hydrocarbons? | Alkanes Cₙ$H_{2}$ₙ₊_{2} (saturated); Alkenes Cₙ$H_{2}$ₙ (one C=C); Alkynes Cₙ$H_{2}$ₙ₋_{2} (one C≡C)

Ethane conformations? | Staggered (60°, most stable, zero torsional strain) vs Eclipsed (0°, least stable, max torsional strain)

Butane stability order? | Anti (180°) > Gauche (60°) > Eclipsed (120°) > Fully eclipsed (0°) — mnemonic: "A Gentle Evening Falls"

3 steps of radical halogenation? | Initiation (UV/heat: $X_{2}$ → 2X•) → Propagation (R–H + X• → R• + HX; R• + $X_{2}$ → R–X + X•) → Termination (R• + R• → R–R)

H-abstraction selectivity? | 3° > 2° > 1°; Halogen selectivity: $Br_{2}$ (most selective) > $Cl_{2}$ > $F_{2}$

Markovnikov's rule? | H adds to C with more H atoms → more stable carbocation intermediate

Anti-Markovnikov — which HX? | ONLY HBr + organic peroxide (Kharasch). NOT HCl (endothermic radical step). NOT HI (premature termination).

Ozonolysis products? | Alkene + $O_{3}$ → ozonide --[Zn/$H_{2}$O]--> aldehydes/ketones. 2-Butene → 2× acetaldehyde.

Alkyne acidity order? | sp (50% s) > $sp^{2}$ (33.3% s) > $sp^{3}$ (25% s). Terminal alkyne + NaN$H_{2}$ → sodium acetylide + $NH_{3}$.

Lindlar's catalyst? | Pd/CaC$O_{3}$ + Pb(OAc)_{2} + quinoline; syn-addition → cis-alkene

Na/liq. $NH_{3}$ (Birch)? | Dissolving metal; radical anion → anti-addition → trans-alkene

Summary

Hydrocarbons are classified by degree of unsaturation. Key reactions: (1) conformational analysis via Newman projections; (2) free radical halogenation (3 steps, $Br_{2}$ most selective); (3) Markovnikov addition (ionic) vs anti-Markovnikov (radical, HBr+peroxide ONLY); (4) ozonolysis locates C=C position; (5) alkynes show sp-hybridized acidic H; (6) Lindlar's → cis, Na/$NH_{3}$ → trans.

Apparatus Reference: Newman Projections of Ethane ($C_{2}H_{6}$)

Staggered H H H H H H Dihedral = 60° · Min. torsional strain Eclipsed H H H H H H Dihedral = 0° · Max. torsional strain