Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 23: Problem 72

All aliphatic amines have about the same hase strength, \(\mathrm{p} K_{\mathrm{2}}\) of the conjugate acid \(10.0-11.0\), and are slightly stronger bases than ammonia. The increase in basicity compared with ammonia can be attributed to the greater stability of an alkylammonium ion, as for example \(\mathrm{RCH}_{2} \mathrm{NH}_{3}{ }^{+}\)compared with the ammonium ion, \(\mathrm{NH}_{4}{ }^{+}\). This greater stability arises from the electron- releasing effect of alky groups and the resulting partial delocalization of the positive charge from nitrogen onto carbon in the alkylammonium ion.

Short Answer

Expert verified
Answer: Aliphatic amines are slightly stronger bases than ammonia because their conjugate acid, the alkylammonium ion, is more stable due to the electron-releasing effect from the alkyl group and the partial delocalization of the positive charge on nitrogen. This stabilization makes the amine more likely to accept a proton, resulting in higher basicity compared to ammonia.

Step by step solution

01

Understand the stability of the alkylammonium ion

Aliphatic amines are slightly stronger bases than ammonia because their conjugate acid, an alkylammonium ion (e.g., \(\mathrm{RCH}_{2} \mathrm{NH}_{3}{ }^{+}\)), is more stable than the ammonium ion (\(\mathrm{NH}_{4}{ }^{+}\)). A stable conjugate acid implies that the amine is willing to accept a proton more easily.
02

Explain the electron-releasing effect

Alkyl groups, such as \(\mathrm{RCH}_{2}\), have a tendency to donate electron density to neighboring atoms. In the case of alkylamines, the alkyl group donates electron density to the adjacent nitrogen atom. This electron-releasing effect stabilizes the positive charge on the nitrogen atom in the alkylammonium ion.
03

Describe partial delocalization of the positive charge

Due to the electron-releasing effect from the alkyl group, there is a partial delocalization of the positive charge on nitrogen. This means that the positive charge is not entirely localized on the nitrogen atom; instead, it is partially spread over the adjacent carbon atom in the alkyl group, which reduces the overall charge density on the nitrogen.
04

Relate the stability to the basicity of amines

Since the positive charge in the alkylammonium ion is partially delocalized and the nitrogen atom is stabilized by the electron-releasing alkyl group, the alkylamine is more likely to accept a proton and act as a base. This results in their slightly higher basicity compared to ammonia, which has a less stable conjugate acid (the ammonium ion) with a more localized positive charge on the nitrogen atom.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

The hasicitydecreasing effect of nitro substitution in the s-position is almost entirely the result of its inductive effect, whereas that of nitro substitution in the 4.position is attributable to both inductive and resonance effects. In the case of para suhstitution (as well as ortho substitution), delocalization of the lone pair on the amino nitrogen involves not only the carbons of the aromatic ring but alwo oxy gen atoms of the nitro group.

Amines are further divided into aliphatic and aromatic amines. In an aliphatic amine, all carbons bonded to nitrogen are derived from alkyl groups; in an aromatic amine, one or more of the groups bonded to nitrogen are aryl groups.

An amine in which the nitrogen atom is part of a ring is classified as a heterocyclic amine. When the nitrogen is part of an aromatic ring (Section 21.2D), the amine is classified as a beterocyclic aromatic amine. Following are structural for mulas for two heterocyclic aliphatic amines and two heterocyclic aromatic amines.

Aromatic amines are considerahly weaker hases than aliphatic amines. Compare, for example, values of \(\mathrm{p} K_{\mathrm{a}}\) for aniline and cyclohexylamine. The ionization constant for the conjugate acid of aniline is lasger (the smaller the value of \(\mathrm{p} K_{\mathrm{a}}\), the weaker the base) than that for cyclohexylamine by a factor of \(10^{6}\).

The geometry of a nitrogen atom bonded to three other atoms or groups of atoms is trigonal pyramidal (Section 1.4). The sp, bybridized nitrogen atom is at the apex of the Pyramid, and the three groups bouded to it extend densaward to form the triangular base of the prramid. If we consider the unshared pair of electrons on nitrogen as a foeurth grosp, then the amrangement of "groups" around nitrogen is approximately tetrahedral. Berause of this geoenetry, an ansine with three different groups bonded to nitrogen is chiral and can exist as a pair of enantiomers, as illustrated by the nonsuperporable mirror images of ethyimethylamine. In assigning configuration to these enantiomers, the groxp of lowest prioxity on nitrogen is the unshared pair of electrons.
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Analysis

Read Explanation

Chemistry Branches

Read Explanation

Chemical Reactions

Read Explanation

Inorganic Chemistry

Read Explanation

Making Measurements

Read Explanation

The Earths Atmosphere

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free