6 Reasoning Chains for OC-02 Problems

Chain 1: Determining Markovnikov vs Anti-Markovnikov Product

Is peroxide present?
→ NO → Ionic mechanism → Apply Markovnikov's rule → H adds to more-H carbon → More stable carbocation → Product
→ YES → Is the HX = HBr?
    → YES → Free radical mechanism → Br• adds to less-substituted C → More stable radical → Anti-Markovnikov product
    → NO (HCl or HI) → No anti-Markovnikov → Ionic Markovnikov product (if HCl) or no useful reaction (if HI)

Chain 2: Predicting Ozonolysis Products

Identify the C=C in the alkene
→ Mentally cleave the C=C bond
→ For each C of the former C=C:
    → Does it have at least 1 H? → YES → Aldehyde (–CHO)
    → Does it have 0 H? → YES → Ketone (–CO–)
→ Name or write SMILES for each fragment
→ These are the products

Chain 3: Choosing Lindlar vs Na/$NH_{3}$ for Desired Alkene Geometry

Do I want cis (Z) alkene from an alkyne?
→ YES → Use Lindlar's catalyst + $H_{2}$ (syn-addition)
→ NO → Do I want trans (E) alkene?
    → YES → Use Na (or Li) in liquid $NH_{3}$ (anti-addition)
    → Do I want complete reduction to alkane?
        → YES → Use $H_{2}$/Pd–C (excess, no poisoning)

Chain 4: Testing Alkyne Acidity

Is the C–H bond sp, $sp^{2}$, or $sp^{3}$?
→ sp (alkyne terminal C–H) → 50% s-character → Most acidic → Can be deprotonated by NaN$H_{2}$
→ $sp^{2}$ (alkene vinylic C–H) → 33.3% s-character → Intermediate acidity → Cannot be deprotonated by NaN$H_{2}$
→ $sp^{3}$ (alkane C–H) → 25% s-character → Least acidic → Cannot be deprotonated by NaN$H_{2}$ or NaOH

Chain 5: Free Radical Halogenation — Predicting Major Product

Which halogen is used?
→ $Br_{2}$ (UV/$\Delta$): Highly selective
    → Is there a 3° carbon? → YES → 3° H abstraction → 3° alkyl bromide is major product
    → No 3°? → Is there a 2° carbon? → YES → 2° H abstraction → 2° alkyl bromide is major
→ $Cl_{2}$ (UV/$\Delta$): Moderately selective
    → All positions compete but 3° > 2° > 1° still applies
    → Statistical factors (number of H at each position) matter more for $Cl_{2}$

Chain 6: Identifying Unknown Alkyne from Reactions

Does compound decolorize $Br_{2}$/$CCl_{4}$? → YES → Unsaturated (alkene or alkyne)
Does compound give precipitate with $AgNO_{3}$/$NH_{3}$? → YES → Terminal alkyne (acidic sp C–H forms silver acetylide)
Does compound react with NaN$H_{2}$? → YES → Terminal alkyne confirmed
Apply Na/liq. $NH_{3}$ → trans-alkene product
Apply Lindlar's + $H_{2}$ → cis-alkene product