Chem 215-1 Midterm 3

Epoxides as substrates conditions?

• Neutral and basic = Sn2 first then proton transfer to make an alcohol

• Acidic = Proton transfer to positive O, S_N2

• START: Epoxides

• END: Depends on reagents

In an epoxide as substrate reaction, why are they able to have an RO^- as a leaving group (ineffective for S_N2 reactions)?

Because epoxides are highly strained, this releases ring strain

In epoxides as substrate reactions, which C does the nucleophile attack?

• Neutral/basic conditions, attacks at the less highly substituted C atom of the ring

• Acidic, attacks at more highly substituted atom

When does Walden inversion occur and what is it?

When a nucleophile attacks a C atom in an S_N2 step, the connected three groups point away from the nucleophile (dashed and wedged stay the same), like an umbrella flipping in and out

Formation of epoxides by nucleophilic substitution conditions?

• START: Halohydrin (looks like a ketone with H on oxygen)

• END: Epoxide

• Proton transfer → S_N2 (oxygen nucleophile attacks itself to close ring with Cl- as leaving group)

What is diazomethane?

CH₂N₂

Diazomethane (CH₂N₂) formation of methyl esters conditions?

• START: Carboxylic acid

• NEED: Diazomethane

• END: Ester with methyl on end (with O)

• Proton transfer → S_N2 (both with diazomethane)

Amines + quaternary ammonium salts from alkyl halides conditions?

• START: Amines

• NEED: alkyl halide

• END: Primary → secondary → tertiary → quaternary amine

• S_N2 → Proton transfer

What does excess NH₃ do for a quaternary ammonium reaction?

Ensures that the alkyl halide reactions with NH₃ rather than the amine product (which would increase the degree of the amine), still decent amount of it though

• Alkylation not that effective to synthesize specific amines (degrees)

What does adding a large excess of alkyl halide do in a quaternary ammonium reaction?

Allows for the formation of a lot of quaternary ammonium ions

Hofmann elimination conditions?

• START: Primary amine

• NEED: Excess CH₃I

• END: anti-Zaitsev product

• S_N2 → Proton transfer → 2 more alkylations → Replaces og S_N2 leaving group with HO^- → E2

Generating alkynes by elimination conditions?

• START: Alkene

• NEED: Base

• END: Alkyne

• E2 → Proton transfer → Proton transfer (acid)

• Leaving group in vinylic position

• Carried out at extreme temperatures, >200 degrees C

• Acid workup

Alkylation of terminal alkyne (reactions that alter the carbon skeleton) conditions?

• START: terminal alkene

• NEED:

• END:

• Proton transfer → S_N2