Ch.22

Question 1

What is alpha substitution?

Answer 1

the substitution of one of the hydrogens attached to the alpha carbon for an electrophile

Question 2

Alpha substitution occurs through an _____ ion intermediate.

Answer 2

enolate

Question 3

What is tautomerization?

Answer 3

an interconversion of isomers that occurs through the migration of a proton and the movement of a double bond

Question 4

Are tautomers resonance forms?

Answer 4

no

Question 5

Describe base-catalyzed tautomerism.

Answer 5

A proton on the a carbon is abstracted to form a resonance-stabilized enolate ion with the negative charge spread over a carbon atom and an oxygen atom

Question 6

Equilibrium in base-catalyzed tautomerism favors which form?

Answer 6

favors keto form over the enolate ion

Question 7

Describe acid-catalyzed tautomerism.

Answer 7

the oxygen is first protonated, and then a proton from the a carbon is removed

Question 8

Describe reacemization.

Answer 8

If a chiral a carbon has an enolizable hydrogen atom, a trace of acid or base allows that carbon to invert its configuration, with the enol serving as the intermediate.

Question 9

What is the pKa for alpha H of aldehyde or ketone?

Answer 9

around 20

Question 10

Which is more acidic, and aldehyde/ketone or alkane/alkene?

Answer 10

aldehyde/ketone

Question 11

What is the approximate pKa of water?

Answer 11

15.7

Question 12

what is the pKa of an alkyne?

Answer 12

25

Question 13

what is the pKa of an alcohol?

Answer 13

16-19

Question 14

Even though the keto–enol tautomerism equilibrium favors the keto form, addition of an ______ ______ the equilibrium toward the formation of more enol

Answer 14

electrophile shifts

Question 15

How is LDA made?

Answer 15

by using an alkyllitium reagent to deprotonate diispropylamine

Question 16

What can LDA do?

Answer 16

convert a carbonyl compound completely to its enolate

Question 17

what happens when LDA reacts with a ketone?

Answer 17

it abstracts the a proton to form the lithium salt of the enolate

Question 18

Ketones or aldehydes react with a secondary amine to form _________.

Answer 18

enamines

Question 19

The enamine has a nucleophilic a carbon, which can be used to attack ___________.

Answer 19

electrophiles

Question 20

The electrostatic potential map (EPM) of a simple enamine shows a what (red) near the a carbon atom of the double bond?

Answer 20

high negative electrostatic potential

Question 21

Enamines displace halides from reactive alkyl halides, giving alkylated _____ __________.

Answer 21

iminium salts

Question 22

The alkylated iminium salt can be hydrolyzed to the ketone under _____ conditions.

Answer 22

acidic

Question 23

Hydrolysis of the iminium salt produces the ______ as the final product.

Answer 23

beta-diketone

Question 24

When a ketone is treated with a halogen and a base, an ____________ reaction occurs.

Answer 24

alpha halogenation

Question 25

What reaction is called base-promoted?

Answer 25

the alpha halogenation of ketone

Question 26

In multiple halogenation, which halogenation occurs faster?

Answer 26

second halogenation

Question 27

In haloform reaction, when Cl2 is used, what is formed?

Answer 27

chloroform

Question 28

In haloform reaction, when Br2 is used, what is formed?

Answer 28

bromoform

Question 29

In haloform reaction, when I2 is used, what is formed?

Answer 29

iodoform

Question 30

What is the iodoform test used to identify?

Answer 30

methyl ketones (or secondary alcohols)

Question 31

Alcohols can give a _____ iodoform test.

Answer 31

positive

Question 32

What is iodoform (CHI3)?

Answer 32

a yellow solid that participates out of solution

Question 33

The _____ reaction replaces a hydrogen atom with a bromine atom on the a carbon of a carboxylic acid (a-bromoacid).

Answer 33

HVZ

Question 34

what do condensations do?

Answer 34

combine two or more molecules, often with the loss of a small molecule such as water or an alcohol

Question 35

what is the aldol condensation?

Answer 35

the addition of an enolate ion to another carbonyl group. It occurs under basic conditions

Question 36

In aldol condensations, When the reaction is carried out at _____ temperatures, the beta-hydroxy carbonyl compound can be isolated

Answer 36

low

Question 37

In aldol condensation, what will heating do?

Answer 37

Heating will dehydrate the aldol product to the alpha,beta-unsaturated compound.

Question 38

what is crossed aldol condensation?

Answer 38

When the enolate of one aldehyde (or ketone) adds to the carbonyl group of a different aldehyde or ketone

Question 39

Intramolecular aldol reactions of diketones are often used for making what?

Answer 39

five- and six-membered rings

Question 40

Is stereo control possible for Mukaiyama Aldol Addition and Alkylation?

Answer 40

yes

Question 41

Is stereo control possible for Henry Reaction?

Answer 41

yes

Question 42

Describe the mannich reaction.

Answer 42

formation of the iminium ion of aldehyde

Question 43

The claisen condensation results when what happens?

Answer 43

when an ester molecule undergoes nucleophilic acyl substitution by an enolate

Question 44

What is an internal Claisen cyclization is called?

Answer 44

a Dieckmann condensation or a Dieckmann cyclization

Question 45

What are useful esters?

Answer 45

benzoates, formates, carbonates, and oxalates

Question 46

_________ may also react with an ester to form a beta-diketone.

Answer 46

ketones

Question 47

What happens in a crossed claisen condensation?

Answer 47

an ester without alpha hydrogens serves as the electrophilic component

Question 48

Which are more acidic, and more likely to deprotonate and serve as the enolate component in the condensation, ketones or esters?

Answer 48

ketones

Question 49

What does malonic ester synthesis make?

Answer 49

substituted derivatives of acetic acids.

Question 50

______ takes place through a cyclic transition state, initially giving an enol form that quickly tautomerizes to the product.

Answer 50

Decarboxylation

Question 51

What are the final products of acetoacetic ester synthesis?

Answer 51

ketones

Question 52

_____ ion completely deprotonates acetoacetic ester.

Answer 52

Ethoxide

Question 53

alpha,beta-Unsaturated carbonyl compounds have unusually _______ double bonds.

Answer 53

electrophilic

Question 54

describe hard nucleophiles.

Answer 54

have low energy HOMO's and a high charge + have high energy LUMO's and a high charge

Question 55

describe soft nucleophiles.

Answer 55

have high energy HOMO's and are polarizable + low energy LUMO's and are polarizable

Question 56

What dominates the reactivity of hard nucleophiles?

Answer 56

charge

Question 57

What dominates the reactivity of soft nucleophiles?

Answer 57

orbital interactions

Question 58

Hard nucleophiles tend to react well with ___ electrophiles.

Answer 58

hard

Question 59

Soft electrophiles tend to react well with ____ nucleophiles.

Answer 59

soft

Question 60

What are some hard basic nucleophiles?

Answer 60

H20, HO-, RCO2-, Cl-, ROH, RO-, NH3, RNH2

Question 61

What are some hard acidic electrophiles?

Answer 61

H+, Li+, Na+, K+, Mg2+, BF3

Question 62

What are some soft basic nucleophiles?

Answer 62

I-, RS-, RSe-, S2-, RSH, RSR, R3P, alkenes, aromatics, R-

Question 63

What are some soft acidic electrophiles?

Answer 63

Ag+, Pd2+, I2, Br2, radicals

Question 64

An enolate will do a ___,___-attack on the a,b-unsaturated ketone (MVK).

Answer 64

1,4

Question 65

Describe robinson annulation.

Answer 65

With enough base, the product of the Michael reaction undergoes a spontaneous intramolecular aldol condensation, usually with dehydration, to give a six-membered ring—a conjugated cyclohexenone