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32.4.19: Chapter 20

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    460331
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    Problem 20-1
    (a) 3-Methylbutanoic acid
    (b) 4-Bromopentanoic acid
    (c) 2-Ethylpentanoic acid
    (d) cis-4-Hexenoic acid
    (e) 2,4-Dimethylpentanenitrile
    (f) cis-1,3-Cyclopentanedicarboxylic acid
    Problem 20-2
    (a) The structure of 2,3-dimethylhexanoic acid. Methyl groups are attached to C 2 and C 3. C 1 is part of the C O O H group.
    (b) The structure of 4-methylpentanoic acid, a five-carbon chain with a methyl group attached to C 4. C 1 is part of the C O O H group.
    (c) The structure of trans-1,2-cyclobutanedicarboxylic acid. C O O H groups are attached to C 1 and C 2 of a cyclobutane ring, trans to one another.
    (d) The structure of o-hydroxybenzoic acid. A C O O H group is present on C 1 of benzene ring. The ortho position is connected to the O H group.
    (e) Structure of (9 Z, 12 Z)-9, 12-octadecadienoic acid. C 9 and C 12 are double-bonded with attached groups in Z configuration. C 1 is part of C O O H.
    (f) The structure of 2-pentenenitrile. A double bond is placed between C 2 and C 3. C 1 is part of the C N group.
    Problem 20-3 Dissolve the mixture in ether, extract with aqueous NaOH, separate and acidify the aqueous layer, and extract with ether.
    Problem 20-4 43%
    Problem 20-5
    (a) 82% dissociation
    (b) 73% dissociation
    Problem 20-6 Lactic acid is stronger because of the inductive effect of the  −OH group.
    Problem 20-7 The dianion is destabilized by repulsion between charges.
    Problem 20-8 More reactive
    Problem 20-9
    (a) p-Methylbenzoic acid < Benzoic acid < p-Chlorobenzoic acid
    (b) Acetic acid < Benzoic acid < p-Nitrobenzoic acid
    Problem 20-10
    (a) 1. Mg; 2. CO2; 3. H3O+
    (b) 1. Mg; 2. CO2; 3. H3O+ or 1. NaCN; 2. H3O+
    Problem 20-11 1. NaCN; 2. H3O+; 3. LiAlH4
    Problem 20-12 1. PBr3; 2. NaCN; 3. H3O+; 4. LiAlH4
    Problem 20-13
    (a) Propanenitrile + CH3CH2MgBr, then H3O+
    (b) p-Chlorobenzonitrile + CH3MgBr, then H3O+
    Problem 20-14 1. NaCN; 2. CH3CH2MgBr, then H3O+
    Problem 20-15 A carboxylic acid has a very broad  − OH absorption at 2500–3300 cm−1.
    Problem 20-16 4-Hydroxycyclohexanone: H–C–O absorption near 4 δ in the 1H spectrum and C═O absorption near 210 δ in the 13C spectrum. Cyclopentanecarboxylic acid: –CO2H absorption near 12 δ in the 1H spectrum and  –CO2H absorption near 170 δ in the 13C spectrum.

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