Chapter 7: Aldehyde and Ketones II

Question 1

the carbonyl carbon is ___________ (electrophilic/nucleophilic)

Answer 1

electrophilic

(positively charged = electron loving)

Question 2

what is an alpha carbon

Answer 2

a carbon directly attached to the carbonyl carbon

Question 3

alpha-hydrogen

Answer 3

a hydrogen attached to an alpha carbon

Question 4

the alpha hydrogen is _________ (acidic/basic). why? (2 reasons)

Answer 4

acidic (deprotonate easily)

the carbonyl oxygen weakens the C-H bond (via induction)

the negative charge between the alpha-carbon, carbonyl carbon, and carbonyl oxygen are all resonance stabilized once the alpha-hydrogen is removed

Question 5

in _____ (acidic/basic) solutions, the alpha hydrogen will easily deprotonate

Answer 5

basic

Question 6

electron-withdrawing groups (example) ________ (stabilize/destabilize) organic anions

Answer 6

stabilize

ex. oxygen

Question 7

electron-donating groups (example) ________ (stabilize/destabilize) organic anions

Answer 7

destabilize

ex. alkyl groups

Question 8

which alpha-hydrogen is slightly more acidic than the other? (aldehydes vs ketones)

why?

Answer 8

aldehydes alpha-hydrogens are slightly more acidic than ketone alpha-hydrogens

the extra (electron-donating) alkyl group of the ketone destabilizes the carbanion, slightly disfavouring the loss of alpha-hydrogens

Question 9

which are slightly more reactive to nucleophiles, aldehydes or ketones? why?

Answer 9

aldehydes

additional steric hindrance of ketone: the alkyl group of ketones are in the way of the nucleophile more than the hydrogen of aldehydes (crowded, higher energy intermediate)

Question 10

keto-enol tautomerization

Answer 10

equilibrium lies far to the keto side (many more keto isomers is solution)

Question 11

tautomers

Answer 11

isomers of a molecule in a solution

interchangeable forms because chemical bonds are rearranged many times spontaneously

Question 12

enolization

Answer 12

enolization or tautomerization

Question 13

enolate (?)

Answer 13

deprotonation of the alpha carbon by a strong base

Question 14

Michael addition reactions (add more later?)

Answer 14

the nucleophilic addition of a carbanion or another nucleophile to an α,β-unsaturated carbonyl compound containing an electron withdrawing group

Question 15

what role does the notate carbanion play in organic reactions?

Answer 15

nucleophile

Question 16

what conditions favour the kinetic enolate?

Answer 16

favoured by fast, irreversible reactions

(ex. strong, sterically hindered base; lower temperatures)

Question 17

what conditons favour the thermodynamic enolate?

Answer 17

favoured by slower, reversible reactions

(ex. weaker/smaller bases; higher temperatures)

Question 18

enamines

Answer 18

tautomers of imines

Question 19

which is thermodynamically favoured, imines or enamines?

Answer 19

imines

Question 20

condensation reaction

Answer 20

two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water

Question 21

aldol condensation

Answer 21

follows same general mechanism as nucleophilic addition to a carbonyl

aldehyde or ketone acts as both an electrophile (keto form) and a nucleophile (enolate form)

Question 22

aldol condensation steps

Answer 22

step 1: forming the aldol

step 2: dehydration of the aldol

Question 23

aldol structure

Answer 23