Organic Chemistry 1 Midterm 3 Review

Alkyne reactions, radical halogenation, substitution reactions, elimination reactions, and synthesis

Addition of Hydrogen Halide (HX)

• Geminal dihalide (two halide substituents on the same carbon)

• Triple bond become single bond

• Markovnikov

• Non-stereoselective

Halogenation (X₂)

• Four halides (two halides on either side)

• Triple bond becomes a single bond

• Non-regioselective

• Anti stereoselectivity

Hydroboration-Oxidation (R₂BH, H₂O₂, NaOH)

• Ketone

• Non-Markovnikov

• Syn Stereoselectivity

Hydrogenation to TRANS-alkene (Na^o, NH₃)

• Triple bond turns into trans-alkene

• Non-regioselectivity

• Anti Stereoselectivity

Hydrogenation to Alkane (H₂, Pd)

• Triple bond becomes single bond

• Non-regioselective

• Syn Stereoselectivity (both H₂ are added to the same face)

Hydrogenation to CIS-Alkene (H₂, Lindlar)

• Triple bond becomes cis-alkene

• Non-regioselective

• Syn Stereoselectivity

Acid-Catalyzed Hydration (H₃O⁺)

• Internal: Ketone racemic mix

• External: Single Ketone

• Markovnikov regioselectivity

• Non-stereoselective

Alkylation (NaH or NaNH₂, R’-X)

• Adds R’ to alkyne in place of H

• Non-regioselective

• Non-stereoselective

Dehydrohalogenation (β-elimination)

Internal: Br₂, NaNH₂

External: Br₂, NaNH₂, H₃O⁺

• Turns double bond to triple bond

• Non-regioselective

• Non-stereoselective

Substitution (Br₂, light/heat)

• Adds a Bromide

• Single bond reactant and product

• Markovnikov

• Non-stereoselective

Allylic Substitution (NBS, light)

• Adds a Br and possibly moves the double bond

• Zaitsev

• Non-stereoselective

Addition of HBr to Alkenes (HBr, ROOR)

• Double bond becomes single bond and a bromide is added

• Non-Markovnikov

• Non-Stereoselective

Radical Stability: What order of stability?

3º > 2º > 1º > sp² > sp

resonance increases stability

Nucleophile Strength: What makes a strong base differ from a weak base?

• Negative charge > neutral

• Bulky strong bases act exclusively as bases and not as nucleophiles

• I^-, Br^-, HS^-, NC^- are good nucleophiles but weak bases (non-basic)

S_N1

• Multi-Step reaction

• First step is the slow step

• Stereochemistry is “lost” (racemic mixture)

• Resonance may occur and must be shown in the energy diagram

S_N2

• Single-Step reaction (simultaneous)

• Backside attack

• Stereochemistry is Inverted

• 1º usually S_N2 unless the base is bulky

E1

• Weak base and 2º or 3º leaving group

• Directly complete with S_N1 so both will occur at once

E2

Strong base and a proton on the carbon next to the leaving group

2º and 3º leaving groups favor E2 over S_N2 due to sterics