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Schaum's Outline of Organic Chemistry

George Hademenos, George Hademenos

Chapter 17

CARBANION-ENOLATES AND ENOLS - all with Video Answers

Educators

Chapter Questions

Problem 1

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01:57

Problem 2

Why is the keto form so much more stable (by about $46-59 \mathrm{~kJ} / \mathrm{mol}$ ) than the enol form?

Ahmed Ali
Ahmed Ali
Numerade Educator
03:01

Problem 2

Write structural formulas for the $\beta$-hydroxycarbonyl compounds and their dehydration products formed by aldol condensations of: $(a)$ butanal, $(b)$ phenylacetaldehyde, $(c)$ diethyl ketone, $(d)$ cyclohexanone, (e) benzaldehyde.

Aadit Sharma
Aadit Sharma
Numerade Educator
03:41

Problem 3

The $\mathrm{C}$ of the $-\mathrm{C}=\mathrm{N}$ group is an electrophilic site capable of being attacked by a carbanion. Show how nitriles like $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{C}=\mathrm{N}$ undergo an aldol-type condensation (Thorpe reaction) with hindered bases.

Ian Kaigh
Ian Kaigh
Numerade Educator
10:06

Problem 3

Compare the mechanisms for $(a)$ base-catalyzed and $(b)$ acid-catalyzed keto-enol tautomerism.

Crystal Wang
Crystal Wang
Numerade Educator
04:28

Problem 4

Racemization, D-exchange, and bromination of carbonyl compounds are also acid-catalyzed. (a) Suggest reasonable mechanisms in which enol is an intermediate. (b) In terms of your mechanisms, are the rate expressions of these reactions the same? (c) Why do enols not add $X_2$ as do alkenes?

Ly Tran
Ly Tran
Numerade Educator
01:18

Problem 5

(a) Show the tautomers of each of the following compounds, which are written as the more stable form: (1) $\mathrm{CH}_3 \mathrm{CHO}$, (2) $\mathrm{C}_6 \mathrm{H}_5 \mathrm{COCH}_3$, (3) $\mathrm{CH}_3 \mathrm{NO}_2$, (4) $\mathrm{Me}_2 \mathrm{C}=\mathrm{NOH}$, and (5) $\mathrm{CH}_3 \mathrm{CH}=\mathrm{NCH}_3$. (b) Which two enols are in equilibrium with (i) 2-butanone, and (ii) 1-phenyl-2-butanone? Which is more stable?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
05:09

Problem 6

(a) Write the structural formulas for the stable keto and enol tautomers of ethyl acetoacetate. (b) Why is this enol much more stable than that of a simple ketone? (c) How can the enol be chemically detected?

Nicholas Sacco
Nicholas Sacco
Numerade Educator
01:54

Problem 7

Reaction of $1 \mathrm{~mol}$ each of $\mathrm{Br}_2$ and $\mathrm{PhCOCH}_2 \mathrm{CH}_3$ in basic solution yields $0.5 \mathrm{~mol}$ of $\mathrm{PhCOCBr}_2 \mathrm{CH}_3$ and $0.5 \mathrm{~mol}$ of unreacted $\mathrm{PhCOCH}_2 \mathrm{CH}_3$. Explain.

Alkendra Singh
Alkendra Singh
Numerade Educator
04:57

Problem 8

(a) Use carbanion-enolate alkylations to synthesize: (i) 2-ethylbutanenitrile, (ii) 3-phenyl-2pentanone, (iii) 2-benzylcyclopentanone. (b) Why can the unsymmetrical ketone in part (ii) be alkylated in good yield?

Nima Gharibi
Nima Gharibi
Numerade Educator
02:25

Problem 9

Use enamines in the following conversions: (a) cyclohexanone to (i) 2-allylcyclohexanone and (ii) 2-acetylcyclohexanone, and (b) 3-pentanone to 2-methyl-1-phenyl-3-pentanone.

Alkendra Singh
Alkendra Singh
Numerade Educator
01:00

Problem 10

Compare the relative acid strengths of 2,4-pentanedione, $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{COCH}_3$ (I); ethyl acetoacetate, $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{COOC}_2 \mathrm{H}_5$ (II); and diethyl malonate, $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OOCCH}_2 \mathrm{COOC}_2 \mathrm{H}_5$ (III). Explain your ranking.

Ahmed Ali
Ahmed Ali
Numerade Educator
01:54

Problem 11

Use malonic ester to prepare (a) 2-ethylbutanoic acid, (b) 3-methylbutanoic acid, (c) 2methylbutanoic acid, $(d)$ trimethylacetic acid.

Grigoriy Sereda
Grigoriy Sereda
Numerade Educator
06:37

Problem 12

Use $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}$ and $\mathrm{H}_2 \mathrm{C}\left(\mathrm{COOC}_2 \mathrm{H}_5\right)_2$ as the only organic reagents to synthesize valeramide, $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CONH}_2$.

Ian Kaigh
Ian Kaigh
Numerade Educator
03:38

Problem 13

Prepare 3-methyl-2-pentanone from acetoacetic ester.

Ronald Prasad
Ronald Prasad
Numerade Educator
03:38

Problem 14

Use AAE (acetoacetic ester) synthesis to prepare the $\beta$-diketone 2,4-hexanedione, $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{COCH}_2 \mathrm{CH}_3$.

Ronald Prasad
Ronald Prasad
Numerade Educator
10:54

Problem 15

Devise a synthesis of $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCH}_2 \mathrm{COOH}$ from acetoacetic ester.

Anupa Sharad Medhekar
Anupa Sharad Medhekar
Numerade Educator
04:36

Problem 16

(a) Show the nucleophilic addition of the malonate carbanion to methyl vinyl ketone and the formation of the final keto product. (b) Show how this product can be converted to a $\delta$-ketoacid.

Tom Rutherford
Tom Rutherford
Numerade Educator
02:44

Problem 17

Cyanoethylation is the replacement of an acidic $\alpha \mathrm{H}$ of a carbonyl compound by a $-\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CN}$ group, using acrylonitrile $\left(\mathrm{CH}_2=\mathrm{CHCN}\right)$ and base. Illustrate with cyclohexanone.

Nicholas Sacco
Nicholas Sacco
Numerade Educator

Problem 18

Suggest a mechanism for the $\mathrm{OH}^{-}$-catalyzed aldol condensation of acetaldehyde.

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03:03

Problem 19

Aldehydes and ketones also undergo acid-catalyzed aldol condensations. Devise a mechanism for this reaction in which an enol is an intermediate.

Tom Rutherford
Tom Rutherford
Numerade Educator
05:46

Problem 21

Mixed aldol condensations are useful if (a) one of the two aldehydes has no $\alpha \mathrm{H},(b)$ a symmetrical ketone reacts with $\mathrm{RCHO}$. Explain and illustrate.

Zubair Abdulla
Zubair Abdulla
Numerade Educator
15:05

Problem 22

Show how the following compounds are made from $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CHO}$. Do not repeat the synthesis of any compound needed in ensuing syntheses.

Tom Rutherford
Tom Rutherford
Numerade Educator
04:44

Problem 23

Crotonaldehyde $\left(\stackrel{\check{C}}{\mathrm{C}} \mathrm{H}_3 \stackrel{\beta}{\mathrm{C}} \mathrm{H}=\stackrel{\pi}{\mathrm{C}} \mathrm{HCH}=\mathrm{O}\right)$ undergoes an aldol condensation with acetaldehyde to form sorbic aldehyde $\left(\mathrm{CH}_3 \mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{O}\right)$. Explain the reactivity and acidity of the $\gamma \mathrm{H}$.

Ian Kaigh
Ian Kaigh
Numerade Educator
10:13

Problem 24

Use aldol condensations to synthesize the following useful compounds from cheap and readily available compounds: $($ a $)$ the food preservative sorbic acid, $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{COOH}$; (b) 2-ethyl-1hexanol; (c) 2-ethyl-1,3-hexanediol, an insect repellant; (d) the humectant pentaerythritol, $\left.\mathrm{C}_{(} \mathrm{CH}_2 \mathrm{OH}\right)_4$.

Zubair Abdulla
Zubair Abdulla
Numerade Educator
01:38

Problem 25

Which of the following alkanes can be synthesized from a self-aldol condensation product of an aldehyde [see Problem 17.24(a)] or a symmetrical ketone? (a) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_3$, (b) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}\left(\mathrm{CH}_3\right) \mathrm{CH}_2 \mathrm{CH}_3$,
(c) $\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{CH}_2 \mathrm{CH}_3$,
(d) $\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{C}\left(\mathrm{CH}_3\right)_3$,
(e) $\left(\mathrm{CH}_3\right)_2 \mathrm{CHCH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_3,(\mathrm{f})\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_2 \mathrm{CHCH}\left(\mathrm{CH}_3\right) \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_3$.

Raghvendra Singh
Raghvendra Singh
Numerade Educator
05:45

Problem 26

Give the structural formulas for the products of the aldol-type condensations indicated in Table 17-2. See Table 17-1 $(a)-(g)$ for the carbanions of these condensations.

Nicholas Sacco
Nicholas Sacco
Numerade Educator
01:27

Problem 27

Give structures of the products from the following condensations:

Raghvendra Singh
Raghvendra Singh
Numerade Educator
06:32

Problem 28

In the Knoevenagel reaction, aldehydes or ketones condense with compounds having a reactive $\mathrm{CH}_2$ between two $\mathrm{C}=\mathrm{O}$ groups. The cocatalysts are both a weak base $\left(\mathrm{RCOO}^{-}\right)$and a weak acid $\left(\mathrm{R}_2 \mathrm{NH}_2^{+}\right)$. Outline the reaction between $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}=\mathrm{O}$ and $\mathrm{H}_2 \mathrm{C}(\mathrm{COOEt})_2$.

Tom Rutherford
Tom Rutherford
Numerade Educator
03:14

Problem 29

Prepare trans-cinnamic acid, $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}=\mathrm{CHCOOH}$, by a Perkin condensation [Problem $17.27(a)$ ],

Ronald Prasad
Ronald Prasad
Numerade Educator
01:30

Problem 31

Write structural formulas for the products from the reaction of $\mathrm{C}_2 \mathrm{H}_5 \mathrm{O}^{-} \mathrm{Na}^{+}$with the following esters:
(a) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOC}_2 \mathrm{H}_5$
(b) $\mathrm{C}_6 \mathrm{H}_5 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5$
(c) $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{O}=\mathrm{C}\left(\mathrm{OC}_2 \mathrm{H}_5\right)_2$

Sima Sarker
Sima Sarker
Numerade Educator
05:20

Problem 32

Ethyl pimelate, $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OOC}\left(\mathrm{CH}_2\right)_5 \mathrm{COOC}_2 \mathrm{H}_5$, reacts with $\mathrm{C}_2 \mathrm{H}_5 \mathrm{O}^{-} \mathrm{Na}^{+}$(Dieckmann condensation) to form a cyclic keto ester, $\mathrm{C}_9 \mathrm{H}_{14} \mathrm{O}_3$. Supply a mechanism for its formation and compare the yields in ethanol and ether as solvents.

James Irizarry
James Irizarry
Numerade Educator
02:49

Problem 33

Account for the fact that tricyanomethane, $(\mathrm{CN})_3 \mathrm{CH}$, is a strong acid $\left(K_u=1\right)$.

Vasu Makani
Vasu Makani
Numerade Educator
00:53

Problem 34

Acetone reacts with LDA in THF and then with trimethylsilyl chloride, $\left(\mathrm{CH}_3\right)_3 \mathrm{SiCl}$, at $-78^{\circ} \mathrm{C}$, to give an enolsilane. ( $a$ ) Give equations for the reactions. (b) Why does $\mathrm{O}$ - rather than $\mathrm{C}$-silylation occur?

MS
Morgan Schnars
Numerade Educator
10:55

Problem 35

Prepare 4-methyl-1-hepten-5-one from $\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_2 \mathrm{C}=\mathrm{O}$ and other needed compounds.

Ronald Prasad
Ronald Prasad
Numerade Educator
03:26

Problem 36

Prepare 3-phenylpropenoic acid from malonic ester and $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Br}$.

Isaac Huidobro
Isaac Huidobro
Numerade Educator
02:01

Problem 37

Can the following ketones be prepared by the acetoacetic ester synthesis? Explain. (a) $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{C}_6 \mathrm{H}_5$, (b) $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{C}\left(\mathrm{CH}_3\right)_3$.

Grigoriy Sereda
Grigoriy Sereda
Numerade Educator
10:55

Problem 38

Use acetoacetic ester (AAE) and any needed alkyl halide or dihalide to prepare: (a) $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{CH}_2 \mathrm{COCH}_3$, (b) cyclobutyl methyl ketone, (c) $\mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COCH}_3$, and (d) 1,3-diacetylcyclopentane.

Ronald Prasad
Ronald Prasad
Numerade Educator
03:56

Problem 39

The Robinson "annelation" reaction for synthesizing fused rings uses Michael addition followed by intramolecular aldol condensation. Illustrate with cyclohexanone and methyl vinyl ketone, $\mathrm{CH}_2=\mathrm{CHCOCH}_3$.

Tom Rutherford
Tom Rutherford
Numerade Educator
01:50

Problem 40

Give the ester or combination of esters needed to prepare the following by a Claisen condensation.

Tom Rutherford
Tom Rutherford
Numerade Educator
00:51

Problem 41

In the biochemical conversion of the sugar glucose to ethanol (alcoholic fermentation) a key step is Formulate this reaction as a reversal of an aldol condensation (retroaldol condensation).

Rebecca Wallace
Rebecca Wallace
Numerade Educator