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Alkynes
Halogenation Reagents Product X 2 (1 equivalent) Dihalo alkene X 2 (2 equivalents) Tetrahalo alkane HX (1 equivalent) Vinyl dihalide HX (in excess) Geminal dihalide Hydration Conditions Oxygen Double Bond Adds To Type Acidic Internal ( ketone ) Markovnikov Basic Terminal ( aldehyde ) Anti-Markovnikov Reduction Reagents Product H 2 + Pt/Pd/Ni Alkane reduction H 2 + Lindlar (Pd/BaSO 4 , quinoline, MeOH) Cis alkene Oxidative Cleavage โ Alkyne โ carbonyl โ Triple bond is cut โ Reagents: โ KMnO 4 , OH-, heat โ H 3 O +
Alkyne Product Internal Two carboxylic acids Terminal One carboxylic acid + CO 2 Alkyne Acidity โ Terminal alkynes are more acidic due to higher s character โ can lose H+ โ Only strong bases can deprotonate alkynes, forming acetylide anion (nucleophile) โ Reagent: Terminal alkyne + NaNH 2 โ Mechanism: Base grabs H+ โ negative charge remains on C โ Acetylide (nucleophile) reacts with methyl or 1ยฐ alkyl halides โ SN2 chain extension โ Reagent: NaNH 2 + RX โ Mechanism: C attacks C โ halide is kicked off Acetylide Addition to Carbonyls โ Acetylide attacks C double bonded to O โ makes alcohol โ Terminal alkyne + NaNH 2 โ acetylide โ NaNH 2 + C double bonded to O โ attacks carbonyl Carbonyl Product Aldehyde Secondary alcohol Ketone Tertiary alcohol
