OCHEM 1 Final

Cerritos College

NaH, DBN, DBU

Strong Base, Weak nucleophile (E2)

HO^-, MeO^-, EtO^-

Strong Base, Strong Nucleophile (SN2, E2)

I^-, Br^-, Cl^-, RS^-, HS^-, RSH, H₂S

Weak base, Strong nucleophile (SN1, SN2)

H₂O, MeOH, EtOH

Weak base and weak nucleophile (SN1, E1)

SN1

• substitution w/ strong nucleophile

• methyl & hydride shifts

• bad sterics

• polar protic solvent

• NO STEREOCHEM

• Weak Bases: alcohols, water, nucleophiles

SN1 - Rate

Rate = k[alkyl halide]

SN2

• one step

• alpha & beta carbon pos is very important

• Polar aprotic solvent: acetone, DMSO, DMF (no h-bond)

• good leaving group

• Back side attack ~ stereochem ~ chiral center inverts

• No shifts

SN2 Rate

Rate = k[alkyl halide][nucleophile]

E1

• Carbocation forms ~ rate determining step

• Hydrogen shift ~ beta hydrogen moves to form alkene or tertiary

  • This works to form the most stable carbocation

• Weak Base: H₂O, Neutral Base,

• Polar Protic Solvent

• Temperature needed

• Zaitsev product forms

• No STEREOCHEM

E1 Rate

Rate = k[alkyl halide]

E2

• strong base moves beta hydrogen to form alkene

• No carbocation

• STEREOCHEM - the beta hydrogen has to be anti to the leaving group

• Strong Base:

  • Small: OH^-, OEt^-, OMe^-

  • t-BuO^-, LDA, DBU/ DBN

• Polar Protic Solvent

• Zaitsev and Hoffman

E2 Rate

Rate = k[Substrate][base]

Reaction 1 - HX Addition

Reagent - HX

Cond: Markovnikov + Methyl/ Hydride shifts + Tertiary (or closest) + 2 step + adds nucleophile

Reaction 2 - HBr + ROOR

Reagent - HBr + ROOR

Cond: Peroxide + Antimarkovnikov + forms terminal Bromines

Reaction 3 - Acid-catalyzed hydration

Reagent - H3O+

Cond: Markonivkov + Equilibrium + forms alcohol

Reaction 3 - Oxymercuration-demurcuration

Reagent:

1. Hg(OAc)2, H2O

2. NaBH4

Cond: no need to mem. mech + can have methyl/ hydride shifts + two part rxn + markonivkov + forms alcohol

Reaction 4 - Hydroboration-oxidation

Reagent:

1. BH3*THF

2. H2O2, NaOH

Cond: peroxides needed + forms alcohol + syn formed with alcohol and beta hydrogen + enantiomers

Reaction 6 - Halogenation of Alkenes

Reagents: Cl2 or Br2

Cond: two halogens attach + triangle forms + carbocation forms + halogens end anti

Reaction 7 - Formation of Halohydrins

Reagents: Br2 + H2O

Cond: alcohol and halogen both attach + attached groups are anti + triangle forms with one of the Halogens + alcohol breaks triangle and attaches

Reaction 8 - Epoxides

Reagents:

1. Peroxy Acid, RCOOOH, mCPBA

2. H3O

Cond: oxygen triangle forms + Syn