ch 7 - Aldehydes and Ketones II Flashcards Preview

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1

alpha-carbon

adjacent to the carbonyl carbon

2

alpha-hydrogens

hydrogens connected to the alpha-carbon

3

acidity of alpha-hydrogens

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.

4

carbanion

molecule with a negatively charged carbon atom

5

enol

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

6

tautomers

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

7

alpha-recemization

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

8

Michael addition

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

9

kinetically controlled product of reaction

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

10

thermodynamically controlled product of reaction

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

11

enamination (tautomerization)

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

12

aldol condensation

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

13

aldol

molecule that contains both an aldehyde and an alcohol functional group

14

steps of aldol condensation reaction

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

15

condensation reaction

two molecules joined with the loss of one molecule

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dehydration reaction

small molecule lost in reactions is water

17

retro-aldol reaction

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

18

what species act as nucleophiles in aldol condensation

enolate carbanion; the deprotonated aldehyde or ketone

19

what species acts as an electrophile in aldol condensation

keto form of the aldehyde or ketone