Chem 261 mechanisms

Question 1

what conditions give the anti-Markonikov product?

Answer 1

HBr and Peroxide (ROOR)

Question 2

Steps of acid catalyzed alkene hydration

Answer 2

• acid protonates alkene (C=C bond broken, C-C remains)
• water (Nu-) added –> OH group added to alkane

Question 3

Oxymercuration/Demercuration steps

Answer 3

• oxymerc. –> addition of HgOAc and OH (reactants: H2O, Mg(OAc)2, THF)
• demerc. –> removal of HgOAc and addition of H (Reactants: NaBrH4

*** NO rearrangements –> no carbocation intermediate

Question 4

3 mechanisms of alkene hydration:

Answer 4

• acid catalyzed
• oxymerc./demerc.
• Hydroboration-oxidation

Question 5

Hydroboration-oxidation steps

Answer 5

• hydroboration –> addition of BH2 and H (syn)
• Oxidation –> removal of BH2 and addition of OH

Question 6

dihalogenation of an alkene steps

Answer 6

• addition of br or cl, 3-membered transition state
• addition of other br or cl from other side (syn addition)

Question 7

reactants in halohydration of alkenes

Answer 7

H2O and X2 (X = Cl or Br)

Question 8

Halohydration adds ___ and ___ across a C=C bond

Answer 8

OH and X (X = Cl or Br)

Question 9

2 options for conditions of 1,2-dihydroxylation:

Answer 9

1.) dilute KMnO4/HO-/H2O/cold

2.)OsO4, pyridine then NaHSO3, H2O

Question 10

Dihydroxylation of an olefin with OsO4 (list steps and other conditions)

Answer 10

• OsO4 and pyridine –> intermediate with Os
• react with NaHSO3 and H2O –> product is formed

Question 11

reactants in oxidative cleavage of alkenes

Answer 11

O3 (ozone), Low temp
–> and a reductive or oxidative workup

Question 12

Steps of oxidative cleavage of alkenes

Answer 12

• add O3 with low temp, as well as a reductive/oxidative workup
• results is fragments due to breaking of double bond (2 carbonyl fragments)

Question 13

why is a phenol not an alcohol?

Answer 13

The OH group is attached to an SP2 C and not a SP3

Question 14

Steps of converting an alcohol to an alkyl halide with PBr3

Answer 14

• protonate OH with PBr3
• PBr2 attaches, Br leaves
• Br attacks from bottom, OHPBr2 leaves
• alkyl halide remains

Question 15

What is the purpose of protonating alcohols

Answer 15

To make them into better leaving groups

Question 16

acronym for an OH protecting group

Answer 16

TBSCl or TBS

Question 17

what is TBAF used for

Answer 17

to remove an alcohol protecting group (ie. TBS)
It is a source of fluoride

Question 18

what can you treat an alkene with that results in an epoxide?

Answer 18

MCPBA (a peroxy acid)

Question 19

Acid catalyzed ring opening of an epoxide results in the ____________ product while basic conditions result in the _____________ product

Answer 19

Markonikov
Anti-Markonikov

Question 20

what 2 functinoal groups are created in an epoxide ring opening?

Answer 20

2 OH groups

Question 21

Hyperconjugation definition

Answer 21

delocalization of Pi electrons, increases stability

Question 22

Hydroboration-Oxidation reactants

Answer 22

1.) BH3/THF
2.) H2O2, NaOH

Question 23

What is the solvent for alkyne dihalogenation?
Note: NOT reactant

Answer 23

CCl4

Question 24

What is the solvent for alkene dihalogenation?
Note: NOT reactant

Answer 24

CCl4

Question 25

What is a polar protic solvent? when is it used?
list some examples

Answer 25

A solvent with an OH or NH bond
Used in E1/SN1 reactions
eg. ethanol, methanol, water

Question 26

What is a polar aprotic solvent? when is it used?
List some examples

Answer 26

A solvent without OH or NH
Used in E2/SN2 reactions
Acetone, DMSO, DMF, THF

Question 27

What are the reactants for an acid catalyzed epoxide ring opening?

Answer 27

Acid (ex. H2SO4)
H2O

Question 28

What are the reactants for an base catalyzed epoxide ring opening?

Answer 28

A strong base (ex. NaOH)

Question 29

conditions for CIS 1, 2-Dihydroxylation

Answer 29

OsO4, NaHSO3
(Similar to dihydroxyltion of an alkene with OsO4)

Question 30

conditions for TRANS 1, 2-Dihydroxylation

Answer 30

MCPBA and H+/H2O
(Similar to the formation of an epoxide and then the opening of its ring with an acid and H2O)