Organic Chemistry
9th Edition
ISBN: 9781305080485
Author: John E. McMurry
Publisher: Cengage Learning
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Chapter 20.SE, Problem 29MP
Naturally occurring compounds called terpenoids, which we'll discuss in Section 27-5, are biosynthesized by a pathway that involves loss of CO2 from 3-phosphomevalonate 5-diphosphate to yield isopentenyl diphosphate. Use curved arrows to show the mechanism of this reaction.
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H₂C
ཏཱཏི 1 ནི
OH
1. Br2, PBг3
2. H₂O
H3C
OH
Br
The a-bromination of carbonyl compounds by Br2 in acetic acid is limited to aldehydes and ketones because acids, esters, and amides don't enolize to a sufficient extent. Carboxylic acids, however, can
be a-brominated by first converting the carboxylic acid to an acid bromide by treatment with PBr3. Following enolization of the acid bromide, Br2 reacts in an a-substitution reaction. Hydrolysis of the
acid bromide completes the reaction.
Draw curved arrows to show the movement of electrons in this step of the mechanism.
Arrow-pushing Instructions
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H3C
Br
Br
+
:::OH2
Br
H₂O
H3C
Br
за
Can you help me understand how to approach this question and explain the mechanism?
Ph3P-CHCH3
H₂C
H3C
Aldehydes and ketones are converted into alkenes by means of a direct nucleophilic addition called the Wittig reaction. In the reaction, a triphenylphosphorine ylide, also called a phosphorane, adds to
an aldehyde/ketone to give a four-membered cyclic intermediate called an oxaphosphetane. The oxaphosphetane is not isolated but instead spontaneously decomposes to release triphenylphosphine
oxide and an alkene.
CH3
00
+
The ylide is formed by reaction of triphenylphosphine, a good nucleophile, with a primary alkyl halide in an SN2 reaction, followed by deprotonation of the carbon with a strong base, such as
butyllithium. The carbonyl carbon and the carbon originally bonded to the halogen become the two carbons with the double bond in the product alkene
X m
CH3
The real value of the Wittig reaction lies in its ability to yield an alkene of predictable structure, as the C=C bond is precisely where the C=O bond was in the reactant and no isomers (other than E/Z
isomers)…
Chapter 20 Solutions
Organic Chemistry
Ch. 20.1 - Give IUPAC names for the following compounds:Ch. 20.1 - Draw structures corresponding to the following...Ch. 20.2 - Prob. 3PCh. 20.2 - The Ka for dichloroacetic acid is 3.32 Ă— 10-2....Ch. 20.3 - Calculate the percentages of dissociated and...Ch. 20.4 - Which would you expect to be a stronger acid, the...Ch. 20.4 - Dicarboxylic acids have two dissociation...Ch. 20.4 - The pKa of p-cyclopropylbenzoic acid is 4.45. Is...Ch. 20.4 - Prob. 9PCh. 20.5 - Prob. 10P
Ch. 20.6 - Prob. 11PCh. 20.6 - How might you carry out the following...Ch. 20.7 - Prob. 13PCh. 20.7 - Prob. 14PCh. 20.8 - Cyclopentanecarboxylic acid and...Ch. 20.8 - Prob. 16PCh. 20.SE - Prob. 17VCCh. 20.SE - Prob. 18VCCh. 20.SE - The following carboxylic acid can’t be prepared...Ch. 20.SE - Electrostatic potential maps of anisole and...Ch. 20.SE - Predict the product(s) and provide the mechanism...Ch. 20.SE - Predict the product(s) and provide the mechanism...Ch. 20.SE - Prob. 23MPCh. 20.SE - Predict the product(s) and provide the complete...Ch. 20.SE - Acid-catalyzed hydrolysis of a nitrile to give a...Ch. 20.SE - Prob. 26MPCh. 20.SE - Naturally occurring compounds called cyanogenic...Ch. 20.SE - 2-Bromo-6, 6-dimethylcyclohexanone gives 2,...Ch. 20.SE - Naturally occurring compounds called terpenoids,...Ch. 20.SE - In the Ritter reaction, an alkene reacts with a...Ch. 20.SE - Give IUPAC names for the following compounds:Ch. 20.SE - Prob. 32APCh. 20.SE - Prob. 33APCh. 20.SE - Prob. 34APCh. 20.SE - Prob. 35APCh. 20.SE - Prob. 36APCh. 20.SE - Prob. 37APCh. 20.SE - Prob. 38APCh. 20.SE - Calculate the Ka's for the following acids: (a)...Ch. 20.SE - Thioglycolic acid, HSCH2CO2H, a substance used in...Ch. 20.SE - Prob. 41APCh. 20.SE - Prob. 42APCh. 20.SE - How could you convert butanoic acid into the...Ch. 20.SE - How could you convert each of the following...Ch. 20.SE - How could you convert butanenitrile into the...Ch. 20.SE - How would you prepare the following compounds from...Ch. 20.SE - Prob. 47APCh. 20.SE - Using 13CO2 as your only source of labeled carbon,...Ch. 20.SE - Prob. 49APCh. 20.SE - Which method-Grignard carboxylation or nitrile...Ch. 20.SE - Prob. 51APCh. 20.SE - Prob. 52APCh. 20.SE - Propose a structure for a compound C6H12O2 that...Ch. 20.SE - Prob. 54APCh. 20.SE - How would you use NMR (either 13C or 1H) to...Ch. 20.SE - Prob. 56APCh. 20.SE - A chemist in need of 2,2-dimethylpentanoic acid...Ch. 20.SE - Prob. 58APCh. 20.SE - Prob. 59APCh. 20.SE - Prob. 60APCh. 20.SE - Prob. 61APCh. 20.SE - Prob. 62APCh. 20.SE - Prob. 63APCh. 20.SE - The following pKa values have been measured....Ch. 20.SE - Identify the missing reagents a-f in the following...Ch. 20.SE - Propose a structure for a compound, C4H7N, that...Ch. 20.SE - Prob. 67APCh. 20.SE - The 1H and 13C NMR spectra below belong to a...Ch. 20.SE - Propose structures for carboxylic acids that show...Ch. 20.SE - Carboxylic acids having a second carbonyl group...
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