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Ch. 2 - Acids and Bases; Functional Groups
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 2 - Acids and Bases; Functional GroupsProblem 40b
Chapter 2, Problem 40b

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.
b. Determine which nitrogen atom is the most basic.

Verified step by step guidance
1
Identify the three nitrogen atoms in the compound: Nitrogen 1 is bonded to an ethyl group and a hydrogen, Nitrogen 2 is part of an amide group, and Nitrogen 3 is part of an imine group.
Consider the electronic environment of each nitrogen atom. Nitrogen 1 is a secondary amine, Nitrogen 2 is an amide nitrogen, and Nitrogen 3 is an imine nitrogen.
Evaluate the basicity of each nitrogen. Basicity is influenced by the availability of the lone pair of electrons on the nitrogen to accept a proton.
Nitrogen 1, being part of a secondary amine, has its lone pair more available for protonation compared to Nitrogen 2 and Nitrogen 3. Amide nitrogen (Nitrogen 2) is less basic due to resonance delocalization of its lone pair with the carbonyl group. Imine nitrogen (Nitrogen 3) is also less basic due to the partial positive charge on the nitrogen from the double bond.
Conclude that Nitrogen 1 is the most basic nitrogen atom in the compound because its lone pair is not involved in resonance and is more available to accept a proton.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Basicity of Nitrogen Atoms

Basicity refers to the ability of a compound to accept protons (H+ ions). In nitrogen-containing compounds, the basicity is influenced by the availability of the lone pair of electrons on the nitrogen atom. The more available the lone pair, the stronger the base. In this case, the nitrogen atom's environment, including steric and electronic effects, will determine its basicity.
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Steric Hindrance

Steric hindrance occurs when the spatial arrangement of atoms in a molecule prevents certain interactions, such as protonation. In the context of nitrogen atoms, if a nitrogen is surrounded by bulky groups, it may be less accessible for protonation, thus affecting its basicity. Understanding the spatial arrangement of the nitrogen atoms in the given compound is crucial for determining which is the most basic.
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Understanding steric effects.

Resonance Effects

Resonance refers to the delocalization of electrons within a molecule, which can stabilize or destabilize certain structures. In nitrogen-containing compounds, resonance can affect the electron density on nitrogen atoms, influencing their basicity. If a nitrogen atom is involved in resonance with a carbonyl or other electronegative groups, it may be less basic due to reduced electron availability for protonation.
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Related Practice
Textbook Question

The Ka of phenylacetic acid is 5.2 × 10−5, and the pKa of propionic acid is 4.87.

a. Calculate the pKa of phenylacetic acid and the Ka of propionic acid.

b. Which of these is the stronger acid? Calculate how much stronger an acid it is.

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Textbook Question

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.

c. Explain why Y is a stronger acid than X.

d. Explain why Z is a stronger acid than Y.

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Textbook Question

The Ka of phenylacetic acid is 5.2 × 10−5, and the pKa of propionic acid is 4.87.

c. Predict whether the following equilibrium will favor the reactants or the products.

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Textbook Question

Predict the products of the following acid–base reactions.

(a) H2SO4 + CH3COO– ⇌

(b) CH3COOH + (CH3)3N: ⇌

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Textbook Question

Hydrogen peroxide (HOOH) has a pKa of 11.6, making it roughly 10,000 times as strong an acid as water (pKa = 15.7). Explain why H2O2 is a stronger acid than H2O.

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Textbook Question

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

a. Draw the important resonance forms of the products of protonation on each of the three nitrogen atoms.

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