Ch. 8 basics

Question 1

Describe Hydrohalogenation reaction mechanism

Answer 1

1. Proton transfer
2. Nucleophilic attack

the alkene is protonated, forming a carbocation intermediate and a bromide ion
the bromide ion functions as a nucleophile and attacks the carbocation intermediate

Question 2

Describe Hydrohalogenation reactions

Answer 2

the treatment of alkenes with HX ( X= Cl, Br, or I)
markovnikov
X on more subsitituted side

Rearrangements CAN occur

if ROOR is added then anti-mark addition occurs

Question 3

What are the three types of hydration reactions and what do they add?

Answer 3

Acid catalyzed
oxymercuration demercuration
hydroboaration/oxidation

Hydration mechanisms add OH and H

Question 4

Describe Acid- Catalyzed Hydration
what are the reagents
mark or anti-mark?
rearrangmemt?

Answer 4

For most simple alkenes, this reaction proceeds via a Markovnikov addition.

The net result is an addition of H and OH across the π bond, with the OH group positioned at the more substituted carbon:

Will rearrange

reagents:
1. H+
2. H2O
( H3O+) ( dilute H2S04)

1. H2SO4
2. H20
   racemic

Question 5

What are the basic steps in the acid catalyzed hydration?

Answer 5

1. proton transfer
2. Nucleophilic attack
3. Proton transfer

Question 6

oxymercuration-demercuration:

Answer 6

A two-step process for the Markovnikov addition of water across an alkene. with this process, carbocation rearrangements do NOT occur

reagents : 1. Hg(OAc)2, H2O
2. NaBH4

Question 7

hydroboration-oxidation

Answer 7

reagents:
1. BH3* THF
2. H2O2, NaOH

Anti-mark addition of a proton and an OH across an alkene

OH on less substituted side

no rearrangements

when two new chiral centers are formed syn addition ( an addition reaction in which two groups are added to the same face of a pi bond)

stereospecific because only two of the possible four stereoisomers are formed.

Question 8

Describe a (catalytic) hydrogenation

Answer 8

the addition of H2 across a double bond in the presence of a metal catalyst ( Pt, Pd,Ni)

result - alkene to alkane

syn addition of enantiomers

Note: meso compounds are possible ( always check for symmetry bc then only one product is formed

Question 9

Describe halogenation

Answer 9

additon of X2 across a double bond
( Br2 or Cl2 )

Both Enantiomers form

Anti- addition ( think about the bromonium Ion)

know mech.

Question 10

describe Halohydrin rxn

Answer 10

when the reaction is performed in the presence of water, the bromonium ion that is initially formed can be captured by a water molecule, rather than bromide
The net result is the addition of Br and OH across the alkene.

OH on more subsituted

reagents
1. x2
2. H20
anti addition
know mech

Question 11

Anti Dihydroxylation

Answer 11

reactions are characterized by the addition of OH and OH across an alkene
Anti addition + En

know mech for epoxide to diol
know why anti is observed

reagents
1. CH3CO3H
2. H30+
or
1. MCPBA
2. H3O+
or

1. RCO3H
2. H3O+

Question 12

Syn Dihydroxylation

Answer 12

Conditions/ Reagents

1. OsO4 (catalytic) 1. KMnO4
2. NMO 2. NaOH
3. OsO4 ( catalytic)
4. O-OH
5. OsO4
6. NaHSO3/H2O

edit card for formating

Question 13

Oxidative Cleavage

Answer 13

1. O3
2. DMS ( or Zn/H30)

the C═C bond is completely split apart to form two C═O bonds. Therefore, issues of stereochemistry and regiochemistry become irrelevant

Question 14

Common Dehydration reaction

Answer 14

H2SO4, heat

Or

H3Po4, heat