Textbook Question
Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly.
(c)
(d)
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Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 6, Problem 35e,f
Show how each compound might be synthesized by the SN2 displacement of an alkyl halide.
e. H2C=CH—CH2CN
f. H—C≡C—CH2CH2CH3
Verified step by step guidance1
Step 1: Identify the target compound and the nucleophile required for the SN2 reaction. For compound (e) H2C=CH—CH2CN, the nucleophile is cyanide ion (CN⁻), and for compound (f) H—C≡C—CH2CH2CH3, the nucleophile is acetylide ion (C≡C⁻).
Step 2: Select an appropriate alkyl halide that can undergo SN2 displacement. For compound (e), the alkyl halide should be H2C=CH—CH2X (where X is a good leaving group, such as Br or I). For compound (f), the alkyl halide should be CH3CH2CH2X.
Step 3: Ensure the reaction conditions favor SN2. Use a polar aprotic solvent like acetone or DMSO to stabilize the nucleophile and avoid steric hindrance. The reaction should proceed with a backside attack of the nucleophile on the carbon attached to the leaving group.
Step 4: Write the reaction mechanism. For compound (e), CN⁻ attacks the carbon in H2C=CH—CH2X, displacing X and forming H2C=CH—CH2CN. For compound (f), C≡C⁻ attacks the carbon in CH3CH2CH2X, displacing X and forming H—C≡C—CH2CH2CH3.
Step 5: Verify the stereochemistry and product formation. SN2 reactions proceed with inversion of configuration at the carbon center if it is chiral. Ensure the final product matches the target compound.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
SN2 Mechanism
The SN2 (substitution nucleophilic bimolecular) mechanism involves a nucleophile attacking an electrophilic carbon atom, leading to the simultaneous displacement of a leaving group. This reaction is characterized by a single concerted step, where the nucleophile approaches the carbon from the opposite side of the leaving group, resulting in an inversion of configuration. The rate of the reaction depends on the concentration of both the nucleophile and the substrate.
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Drawing the SN2 Mechanism
Alkyl Halides
Alkyl halides are organic compounds containing a carbon atom bonded to a halogen atom (F, Cl, Br, or I). They serve as key substrates in SN2 reactions due to the polar nature of the carbon-halogen bond, which makes the carbon susceptible to nucleophilic attack. The structure of the alkyl halide, including steric hindrance and the type of halogen, significantly influences the reactivity and outcome of the SN2 reaction.
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Nucleophiles
Nucleophiles are species that donate an electron pair to form a chemical bond in a reaction. In the context of SN2 reactions, strong nucleophiles are essential for effectively displacing the leaving group from the alkyl halide. Common nucleophiles include anions like CN⁻ or neutral molecules with lone pairs, such as amines. The strength and sterics of the nucleophile can greatly affect the reaction rate and product formation.
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Related Practice
Textbook Question
When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether.
CH3CH2–Br + (CH3)3C–O–K+ → (CH3)3C–O–CH2CH3 ethyl bromide potassium tert-butoxide ethyl tert-butyl ether
a. What happens to the reaction rate if the concentration of ethyl bromide is doubled?
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Textbook Question
Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly.
(a) (CH3CH2)2CH—Cl or (CH3)3C—Cl
(b)
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Textbook Question
When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether.
CH3CH2–Br + (CH3)3C–O–K+ → (CH3)3C–O–CH2CH3 ethyl bromide potassium tert-butoxide ethyl tert-butyl ether
b. What happens to the rate if the concentration of potassium tert-butoxide is tripled and the concentration of ethyl bromide is doubled?
c. What happens to the rate if the temperature is raised?
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Textbook Question
Predict the compound in each pair that will undergo the SN2 reaction faster.
(c)
(d)
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Textbook Question
Give two syntheses for (CH3)2CH—O—CH2CH3, and explain which synthesis is better.
1971
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