CHEM 2211 Exam 4

What is Zaitsev’s rule?

Remove the most substituted beta-hydrogen, unless: 1) F is the leaving group, 2) a bulky base is used, 3) the more substituted beta-hydrogen cannot adopt anti-PPL (only applies to cyclic rings)

What is the rate for a Sn1 mechanism?

rate = k[AH]

What is the rate for a E1 mechanism?

rate = k[AH]

What is the rate for a Sn2 mechanism?

rate = k[AH][Nu-]

What is the rate for a E2 mechanism?

rate = [AH][B-]

What is the reactivity for Sn2 electrophile?

methyl > 1º > 2º > 3º

What is the reactivity for Sn1, E1, and E2 electrophile?

3º > 2º > 1º > methyl

What happens with polar protic solvents?

H-bonding stabilizes cation, best for Sn1/E1, larger Nu- are better, ex: CH3OH, H2O, NH3

What happens with polar aprotic solvents?

No H-bonding present, best for Sn2/E2, smaller Nu- are better, ex: THF, DCM, DMSO

Substrate for Sn1 mechanism

3º AH

Substrate for E1 mechanism

3º > 2º > 1º AH

Substrate for Sn2 mechanism

1º or 2º AH

Substrate for E2 mechanism

3º > 2º > 1º AH

Product stereochemistry for Sn1 mechanism

equal amounts of R & S

Product stereochemistry for E1 mechanism

Zaitsev’s rules, largest groups on opposite sides of the double bond (E or Z)

Product stereochemistry for Sn2 mechanism

100% INVERSION

Product stereochemistry for E2 mechanism

Zaitsev’s rules, anti-periplanar conformation required

What is the Sn1 mechanism favored by?

Low temperatures, polar protic solvent

What is the E1 mechanism favored by?

Higher temperatures, polar protic solvent

What is the Sn2 mechanism favored by?

Strong Nu-, weak B- (SN/WB), polar aprotic solvent

What is the E2 mechanism favored by?

Strong B-, weak Nu- (WN/SB), polar aprotic solvent

What does stereospecific mean?

The stereochemistry of the starting material dictates the stereochemistry of the product

Sn2 reactions are always stereospecific if the starting material is chiral

E2 reactions may be stereospecific if there is only one beta-hydrogen available to be removed

What does stereoselective mean?

A reaction that produces 2 possible products, but one in higher amounts than the other

E2 reactions may be stereoselective if there are 2 beta-hydrogens available to be removed (E is favored)

E1 reactions are stereoselective as they favor the E alkene over the Z alkene

When you have a strong nucleophile, which reaction is more likely to take place?

Sn2, but E2 if there is a strong but HINDERED base

If there is a bulky base, which reaction mechanism will take place?

E2

Is a neutral sulfur a strong or weak nucleophile?

strong

In polar aprotic solvents, what atoms are better nucleophiles?

Small

In polar protic solvents, what atroms are better nucelophiles?

Big

What kind of hybridization can Sn2 not take place with?

sp2

What is the R and S for hydrohalogenation?

R: Mark, S: no pref

What is the R and S for modified hydrobromination?

R: Anti-Mark, S: no pref

What is the R and S for acid-catalyzed hydration?

R: Mark, S: no pref

What is the R and S for acid-catalyzed ether formation?

R: Mark, S: no pref

What is the R and S for oxymercuration-demercuration?

R: Mark, S: no pref

What is the R and S for modified oxymercuration-demercuration?

R: Mark, S: no pref

What is the R and S for halogenation?

R: Mark, S: Anti

What is the R and S for halohydrin formation?

R: Mark, S: Anti

What is the R and S for haloether formation?

R: Mark, S: Anti

What is the R and S for hydroboration-oxidation?

R: Anti-Mark, S: Syn

What is the R and S for syn dihydroxylation?

R: N/A, S: Syn

What is the R and S for epoxide formation via peroxyacid, epoxide formation via halohydrin, and anti dihydroxylation?

R: N/A, S: Syn

What is the R and S for hydrogenation?

R: N/A, S: Syn

What is the R and S for ozonolysis?

R: N/A, S: N/A

Which reactions have a carbocation intermediate with possible rearrangement?

Hydrohalogenation, acid-catalyzed hydration, and acid-catalyzed ether formation