Textbook Question
Explain the difference in reactivity between CH3O+H2 and CH3OH in a nucleophilic substitution reaction. (The pKa of H3O+ is −1.7.)
721
views
Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
All textbooks
Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 1
Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 1Chapter 11, Problem 1
Why are NH3 and CH3NH2 no longer nucleophiles when they are protonated?
Verified step by step guidance1
Understand the concept of nucleophiles: Nucleophiles are species that donate a pair of electrons to form a new covalent bond. They are typically rich in electrons and have a lone pair that can be donated.
Consider the structure of NH3 (ammonia) and CH3NH2 (methylamine): Both have a nitrogen atom with a lone pair of electrons, making them good nucleophiles in their neutral form.
Analyze what happens when NH3 and CH3NH2 are protonated: Protonation involves the addition of a proton (H⁺) to the molecule, which results in NH4⁺ (ammonium ion) and CH3NH3⁺ (methylammonium ion), respectively.
Examine the effect of protonation on electron availability: When NH3 and CH3NH2 are protonated, the lone pair of electrons on the nitrogen is used to form a bond with the added proton. This means the lone pair is no longer available for donation, reducing their nucleophilicity.
Conclude why protonated forms are not nucleophiles: Since the lone pair is occupied in bonding with the proton, NH4⁺ and CH3NH3⁺ lack the electron pair needed to act as nucleophiles, thus they are no longer nucleophiles.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilicity
Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. Nucleophiles are typically electron-rich species, such as amines like NH3 and CH3NH2, which have lone pairs of electrons that can be used for bonding. When these nucleophiles are protonated, they become positively charged, which significantly reduces their electron density and ability to donate electrons.
Recommended video:
Guided course
08:27
Nucleophilic Addition
Protonation
Protonation is the addition of a proton (H+) to a molecule, resulting in the formation of a positively charged species. In the case of NH3 and CH3NH2, protonation leads to the formation of NH4+ and CH3NH3+, respectively. This process alters the electronic structure of the molecules, making them less capable of acting as nucleophiles due to the increased positive charge that repels electron donation.
Recommended video:
Guided course
03:Proton Splitting
Charge and Reactivity
The charge of a molecule significantly influences its reactivity and ability to participate in chemical reactions. Neutral nucleophiles, like NH3 and CH3NH2, can readily attack electrophiles due to their electron-rich nature. However, once protonated, the resulting cations (NH4+ and CH3NH3+) are stabilized by their positive charge, which makes them less reactive towards electrophiles, effectively rendering them non-nucleophilic.
Recommended video:
Guided course
01:34Calculating formal and net charge.