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Basicity of Heterocyclic Aromatic Amines

Basicity of Heterocyclic Aromatic Amines

Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).

2° Amines to N-Nitrosamines: Reaction with NaNO2

2° Amines to N-Nitrosamines: Reaction with NaNO₂

Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.

meta-Directing Deactivators: –NO2, –CN, –CHO, –&NoBreak;CO2R, –COR, –CO2H

meta-Directing Deactivators: –NO₂, –CN, –CHO, –⁠CO₂R, –COR, –CO₂H

All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for the...

Preparation of Nitriles

Preparation of Nitriles

One of the common methods to prepare nitriles is the dehydration of amides. This method requires strong dehydrating agents like phosphorous pentoxide or boiling acetic anhydride for converting amides to nitriles. Another reagent namely, thionyl chloride also accomplishes the dehydration of amides, where amide acts as a nucleophile. The first step of the mechanism involves the nucleophilic attack by the amide on the thionyl chloride to form an intermediate. In the next step, the electron pairs...

ortho–para-Directing Activators: –CH3, –OH, –&NoBreak;NH2, –OCH3

ortho–para-Directing Activators: –CH₃, –OH, –⁠NH₂, –OCH₃

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...

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Related Experiment Video

Updated: Jun 1, 2026

Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate

Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate

Published on: April 24, 2018

2-Chloro-3-nitro-pyridine.

¹Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.

Acta Crystallographica. Section E, Structure Reports Online

|May 18, 2011

Summary

This summary is machine-generated.

This study details the molecular structure of a pyridine derivative, C5H3ClN2O2. Researchers observed a significant twist in the nitro group and identified intermolecular hydrogen bonds contributing to a layered crystal structure.

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Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate

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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

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Area of Science:

Crystallography
Organic Chemistry
Molecular Structure

Background:

Understanding the precise arrangement of atoms in organic molecules is crucial for predicting their properties and reactivity.
Pyridine derivatives are important scaffolds in medicinal chemistry and materials science.

Purpose of the Study:

To elucidate the crystal structure and intermolecular interactions of the title compound, C5H3ClN2O2.
To analyze the conformational details of the nitro group relative to the pyridine ring.

Main Methods:

Single-crystal X-ray diffraction was employed to determine the three-dimensional molecular and crystal structure.
Analysis of intermolecular interactions, including hydrogen bonding, was performed.

Main Results:

The crystal structure of C5H3ClN2O2 was successfully determined.
A notable twist of 38.5(2)° was observed between the nitro group and the pyridine ring.
Non-classical hydrogen bonds (C-H⋯N and C-H⋯O) were identified, leading to a layered motif in the crystal.

Conclusions:

The study provides detailed structural insights into this specific pyridine derivative.
The observed structural features, including the nitro group twist and hydrogen bonding network, offer a basis for understanding its solid-state behavior and potential applications.