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Related Concept Videos

Basicity of Aromatic Amines01:18

Basicity of Aromatic Amines

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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...
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Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

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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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Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

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Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...
7.1K
Acidity and Basicity of Alcohols and Phenols02:36

Acidity and Basicity of Alcohols and Phenols

22.8K
Like water, alcohols are weak acids and bases. This is attributed to the polarization of the O–H bond making the hydrogen partially positive. Moreover, the electron pairs on the oxygen atom of alcohol make it both basic and nucleophilic. Protonation of an alcohol converts hydroxide, a poor leaving group, into water—a good one. The two acid–base equilibria corresponding to ethanol are depicted below.
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Exceptions to the Octet Rule02:55

Exceptions to the Octet Rule

38.5K
Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:
38.5K
Acidity and Basicity of Carboxylic Acid Derivatives01:25

Acidity and Basicity of Carboxylic Acid Derivatives

4.5K
Carboxylic acids are the strongest among organic acids, as they readily lose the hydroxyl proton to form a resonance-stabilized carboxylate ion. In comparison, the acid derivatives lack acidic hydrogens directly attached to a functional group. In these compounds, the acidic nature arises from their ability to lose α hydrogens, making them weakly acidic.
The relative acidic strength of the derivatives can be explained based on the extent of resonance stabilization of the conjugate base. The...
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Related Experiment Video

Updated: Mar 19, 2026

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography
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Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

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Gas phase basicities of polyfunctional molecules. Part 5: Non-aromatic sp2 nitrogen containing compounds.

Guy Bouchoux1,2, Mirjana Eckert-Maksic3

  • 1Département de Chimie, Laboratoire de Chimie Moléculaire, UMR CNRS 9168, Ecole Polytechnique, Palaiseau, 91120, France.

Mass Spectrometry Reviews
|June 9, 2016
PubMed
Summary

This review examines the gas-phase protonation of non-aromatic molecules with sp2 nitrogen atoms, including imines, amidines, and guanidines. It provides thermochemical data and computational insights for these important functional groups.

Keywords:
intramolecular hydrogen bondsmass spectrometryprotonationquantum chemical calculationssubstituent effectsthermochemistry

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On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes
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On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes

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Determination of the Gas-phase Acidities of Oligopeptides
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Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography
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On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes
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Determination of the Gas-phase Acidities of Oligopeptides
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Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Organic Chemistry

Background:

  • This study is the fifth in a series reviewing gas-phase protonation thermochemistry of polyfunctional molecules.
  • Focuses on non-aromatic molecules with lone pairs on sp2 hybridized nitrogen atoms.

Purpose of the Study:

  • To review and analyze the gas-phase protonation thermochemistry of various nitrogen-containing functional groups.
  • To present experimental data re-evaluated on a consistent basicity scale and provide computational insights.

Main Methods:

  • Review and re-evaluation of experimental data on protonation energetics.
  • Utilized G4MP2 quantum chemistry computations for structural and energetic analysis.
  • Organized findings into five major chapters based on functional groups.

Main Results:

  • Comprehensive data on the protonation of imines, amidines, guanidines, diazenes, hydrazines, oximes, and phosphazenes.
  • Re-evaluated experimental data using a standardized basicity scale (PA(NH3) = 853.6 kJ/mol, GB(NH3) = 819 kJ/mol).
  • Presented structural and energetic information from G4MP2 computations.

Conclusions:

  • Provides a valuable resource for understanding the protonation behavior of diverse nitrogen-containing functional groups.
  • Highlights the importance of computational methods in elucidating thermochemical properties.
  • Establishes a consistent dataset for gas-phase protonation of non-aromatic sp2 nitrogen compounds.