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Updated: Jun 1, 2026
05:07
Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines
Published on: June 23, 2019
N-(Pyrazin-2-yl)aniline.
Wan Ainna Mardhiah Wan Saffiee1, Azila Idris, Zanariah Abdullah
1Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.
Summary
This study details the crystal structure of a nitrogen-containing aromatic compound, C(10)H(9)N(3). Researchers observed a specific inclination between its aromatic rings and hydrogen bonding that forms molecular chains.
Area of Science:
- Crystallography
- Organic Chemistry
- Molecular Structure
Background:
- Understanding the three-dimensional arrangement of atoms in organic molecules is crucial for predicting their properties and reactivity.
- Aromatic compounds with amino groups exhibit diverse structural motifs and intermolecular interactions.
Purpose of the Study:
- To elucidate the crystal structure of the title compound, C(10)H(9)N(3).
- To analyze the molecular geometry and intermolecular interactions, specifically hydrogen bonding, within the crystal lattice.
Main Methods:
- Single-crystal X-ray diffraction was employed to determine the molecular structure.
- Analysis of bond angles, distances, and intermolecular contacts was performed.
Main Results:
- The crystal structure reveals two aromatic rings inclined at an angle of 15.2(1)°.
- The amino nitrogen atom exhibits an expanded bond angle of 130.4(1)°.
- A hydrogen bond between the amino nitrogen and a nitrogen atom of an adjacent molecule was identified, leading to a chain motif.
Conclusions:
- The determined structure provides detailed insights into the solid-state conformation of C(10)H(9)N(3).
- The observed hydrogen bonding pattern highlights a common self-assembly mechanism in related aromatic amines.
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01:10Nomenclature of Aryl and Heterocyclic Amines
The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated for this skeleton. As shown in Figure 1, the common names of the functionalized anilines involve prefixes ortho-, meta-, and para- to indicate the substitution position. Different functionalized aniline derivatives also have notable trivial names.
01:25Basicity 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).
01:18Basicity of Aromatic Amines
The basicity of aromatic amines is much weaker than that of aliphatic amines due to the involvement of the lone pair of electrons over the N atom in resonance with the aryl rings. Generally, the electron-donating ability of any substituents on the aryl ring of aromatic amines increases the basicity of the amine by increasing electron density, and hence the availability of lone pair on the nitrogen. On the other hand, electron-withdrawing functional groups on the aryl ring of amines decrease the...
01:19Diazonium Group Substitution: –OH and –H
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
01:26Physical Properties of Amines
Amines with low molecular weight are usually gaseous at room temperature, while those with high molecular weight are liquid or solids in nature. Usually, low molecular weight amines have a rotten fish-like smell. Diamines typically have a pungent smell. For instance, cadaverine and putrescine, depicted in Figure 1, are two molecules responsible for decaying tissue.
01:11Aryldiazonium Salts to Azo Dyes: Diazo Coupling
The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.