ch 7 - Aldehydes and Ketones II

Question 1

alpha-carbon

Answer 1

adjacent to the carbonyl carbon

Question 2

alpha-hydrogens

Answer 2

hydrogens connected to the alpha-carbon

Question 3

acidity of alpha-hydrogens

Answer 3

augmented by resonance stabilization of the conjugate base; when alpha-hydrogen is removed, the extra electrons that remain can resonate between the alpha-carbon, the carbonyl carbon, and the carbonyl oxygen which increases stability of this enolate intermediate.

Question 4

carbanion

Answer 4

molecule with a negatively charged carbon atom

Question 5

enol

Answer 5

gets name from presence of carbon-carbon double bond (the en-component) and an alcohol (the -ol); one of two isomers of aldehydes and ketones that exist in solution

Question 6

tautomers

Answer 6

two isomers (keto, enol) of aldehydes or ketones that exist in solution; they differ in the placement of a proton and the double bond; equilibrium lies far to keto side so there are more of these

Question 7

alpha-recemization

Answer 7

process through which any aldehyde or ketone with a chiral alpha-carbon will rapidly become a racemic mixture as the keto and enol forms interconvert

Question 8

Michael addition

Answer 8

the nucleophilic enolate carbanion attacks an alpha, beta-unsaturated carbonyl compound - a molecule with a multiple bond between the alpha- and beta-carbons next to a carbonyl

Question 9

kinetically controlled product of reaction

Answer 9

formed more rapidly but is less stable; has the double bond to the less substituted alpha-carbon; formed by the removal of the alpha-hydrogen from the less substituted alpha-carbon because it offers less steric hindrance; favored in reactions that are rapid, irreversible, at lower temps, and with strong, sterically hindered base

Question 10

thermodynamically controlled product of reaction

Answer 10

formed more slowly but more stable; double bond formed with the more substituted alpha-carbon; formed by removal of alpha-hydrogen from the more substituted alpha-carbon; favored with higher temps, slow, reversible reactions, and weaker smaller bases

Question 11

enamination (tautomerization)

Answer 11

imine tautomerized to enamine: from C-C(double bond)N-CH3 to C(double bond)C-N-CH3; imine form is thermodynamically favored

Question 12

aldol condensation

Answer 12

follows same general mechanism for nucleophilic addition to a carbonyl but an aldehyde or ketone acts both as an electrophile (in its keto form) and a nucleophile (in its enolate form), and the end result is the formation of a carbon-carbon bond

Question 13

aldol

Answer 13

molecule that contains both an aldehyde and an alcohol functional group

Question 14

steps of aldol condensation reaction

Answer 14

step 1: form the aldol: an enolate ion is formed, which then attacks the carbonyl carbon forming the aldol; step 2: dehydration of the aldol: the -OH is removed as water (dehydration), forming a double bond

Question 15

condensation reaction

Answer 15

two molecules joined with the loss of one molecule

Question 16

dehydration reaction

Answer 16

small molecule lost in reactions is water

Question 17

retro-aldol reaction

Answer 17

reverse of aldol condensation reaction: aqueous base is added and heat is applied; useful for breaking bonds between alpha- and beta-carbons of a carbonyl

Question 18

what species act as nucleophiles in aldol condensation

Answer 18

enolate carbanion; the deprotonated aldehyde or ketone

Question 19

what species acts as an electrophile in aldol condensation

Answer 19

keto form of the aldehyde or ketone