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Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines
Published on: June 23, 2019
4-Methyl-3-nitro-pyridin-2-amine.
Summary
This study details the crystal structure of a nitro-substituted pyridine compound. Key findings include specific dihedral angles, intramolecular hydrogen bonding, and crystal packing stabilized by pi-pi stacking interactions.
Area of Science:
- Crystallography
- Organic Chemistry
- Molecular Structure
Background:
- Understanding the molecular arrangement and intermolecular forces in organic compounds is crucial for predicting their physical and chemical properties.
- Pyridine derivatives with nitro groups are important in various chemical applications, necessitating detailed structural analysis.
Purpose of the Study:
- To elucidate the crystal structure of the title compound, C(6)H(7)N(3)O(2).
- To investigate the intermolecular interactions, hydrogen bonding, and packing motifs within the crystal lattice.
Main Methods:
- Single-crystal X-ray diffraction analysis was employed to determine the three-dimensional structure.
- Analysis of hydrogen bonding and non-covalent interactions, including pi-pi stacking, was performed.
Main Results:
- The dihedral angle between the nitro group and the pyridine ring was determined to be 15.5(3)°.
- An intramolecular N-H⋯O hydrogen bond was identified.
- The crystal structure features inversion dimers linked by N-H⋯N hydrogen bonds, forming R(2)(2)(8) rings.
- Crystal packing is stabilized by aromatic π-π stacking (centroid-centroid distance = 3.5666(15) Å) and a short N-O⋯π contact.
Conclusions:
- The study provides a detailed structural characterization of the nitro-substituted pyridine compound.
- The identified hydrogen bonding and π-π stacking interactions are key factors governing the crystal packing and stability.
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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.
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).
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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.
01:26Physical 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.
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