Exam 4 O Nucleophile

Question 1

Add water to aldehyde or ketone

Answer 1

Get hydrate

Question 2

Hydrate

Answer 2

Two OH’s

Question 3

The rate of reaction forming a hydrate is relatively slow under neutral conditions but is readily enhanced by

Answer 3

the presence of either acid or base

The reaction can be acid catalyzed or base catalyzed allowing the equilibrium to be achieved quicker

Question 4

Base Catalyzed Hydrate

Answer 4

OH (nucleophile) attacks at the bottom of the aldehyde or ketone, attaching the OH and removing the double bond to the aldehyde or ketone oxygen. That oxygen then attacks water, giving an end product with 2 OH groups attached

Question 5

In the base-catalyzed hydrate reaction hydroxide serves as

Answer 5

a catalyst for the addition of water across the carbonyl group

Question 6

Acid Catalyzed Hydrate

Answer 6

The oxygen from the aldehyde or ketone attacks the H on H3O and takes the H giving an OH with the O being positive. The remaining H2O molecule attacks the side of the double bond to the oxygen and attaches to the molecule and removes the double bond. Water comes in again and attacks the H on the H2O that just attached leaving the end product with 2 OHs

Question 7

For most ketones, hydrate formation is unfavorable because

Answer 7

the equilibrium favors the ketone rather than the hydrate, except for CF3 as the R groups

Question 8

In acidic conditions, an aldehyde or ketone will react with two molecules of alcohol to form

Answer 8

An acetal

Question 9

Acetal

Answer 9

Two OR groups

Question 10

Common acids to make an acetal from aldehydes and ketones

Answer 10

TsOH and H2SO4

Question 11

In the presence of an acid when making an acetal, the carbonyl group is protonated, rendering the carbon atom

Answer 11

More electrophilic

The alcohol is a weak nucleophile so the carbon must be a strong electrophile

Question 12

Acetal formation PAGE 925 LOOK UP and PUT ON CHEAT SHEET

Answer 12

1. The carbonyl group is protonated by attacking the H-A and becomes OH with a positive charge on the O
2. The alcohol attacks the protonated carbonyl and attaches the whole molecule to the starting material by the O from the alcohol
3. The alcohol is deprotonated forming a hemiacetal: making the alcohol OR instead of HOR
4. The OH that is left attacks H-A making it a good leaving group

Question 13

Hemiacetal

Answer 13

1 OH and 1 OR attached to the molecule

Intermediate step in acetal formation

Question 14

During acetal formation, the acid is

Answer 14

not consumed when making the hemiacetal

Question 15

First three steps to Acetal formation

Answer 15

Make the Hemiacetal

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

Question 16

Last four steps of Acetal formation

Answer 16

4. Proton transfer
5. Loss of a leaving group
6. Nucleophilic attack
7. Proton transfer
   Ends with 2 OR groups

Question 17

The middle steps of the last half of acetal formation cannot occur simultaneously because

Answer 17

That would represent SN2 process at a sterically hindered substrate
Instead the leaving group leaves first to form a resonance-stabilized intermediate, which is then attacked by the nucleophile in a separate step

Question 18

For many simple aldehyde, equilibrium favors the formation of

Answer 18

The acetal

Question 19

Most ketones equilibrium favors

Answer 19

Reactants rather than products
Therfore, formation of the acetal happens when one of the products (water) is removed via a special distillation technique

Question 20

Acetal formation requires

Answer 20

2 equivalents of the alcohol (ROH) for every molecule of ketone or a compound containing two OH groups can be used to form a cyclic acetal

Question 21

Cyclic acetal formation

Answer 21

ketone + a compound containing two OH groups