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Related Concept Videos

Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

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...
Basicity of Heterocyclic Aromatic Amines01:25

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).
Acidity and Basicity of Alcohols and Phenols02:36

Acidity and Basicity of Alcohols and Phenols

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.
Basicity of Aromatic Amines01:18

Basicity 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...
Acid Strength and Molecular Structure03:05

Acid Strength and Molecular Structure

Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Acidity and Basicity of Carboxylic Acid Derivatives01:25

Acidity and Basicity of Carboxylic Acid Derivatives

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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Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)
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Experimental gas-phase basicity scale of superbasic phosphazenes.

Ivari Kaljurand1, Ilmar A Koppel, Agnes Kütt

  • 1Department of Chemistry, University of Tartu, Jakobi 2 str, 51014 Tartu, Estonia.

The Journal of Physical Chemistry. A
|February 3, 2007
PubMed
Summary

New organic superbasic phosphazenes and Verkade's bases extend the experimental gas-phase basicity scale. This research establishes a self-consistent scale for strong bases, enhancing accessibility for future studies.

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Area of Science:

  • Organic Chemistry
  • Physical Chemistry
  • Computational Chemistry

Background:

  • The superbasic region of the gas-phase basicity (GB) scale was previously dominated by metal hydroxide bases.
  • Extending this scale with organic bases is crucial for broader accessibility and study.
  • Superbasic phosphazenes and Verkade's bases are potent organic bases with unique structural properties.

Purpose of the Study:

  • To supplement and extend the experimental gas-phase basicity scale in the superbasic region.
  • To determine, for the first time, the gas-phase basicity values for 19 strong organic bases, including novel phosphazenes and Verkade's bases.
  • To establish a self-consistent experimental gas-phase basicity scale between 1020 and 1107 kJ/mol using organic bases.

Main Methods:

  • Experimental determination of gas-phase basicity (GB) values for 17 superbasic phosphazenes and 2 Verkade's bases.
  • Utilizing established techniques to measure GB values for strong organic bases.
  • Computational calculations using density functional theory (DFT) at the B3LYP/6-311+G** level to predict GB values.

Main Results:

  • Experimental GB values were determined for the first time for 19 strong organic bases, including BEMP, a Verkade's base, Et-P2 phosphazene, and t-Bu-P1 phosphazene.
  • Experimental GB values were also determined for the first time for P2 phosphazenes.
  • A self-consistent experimental gas-phase basicity scale from 1020 to 1107 kJ/mol was established, now including organic bases.
  • DFT calculations showed a standard deviation of 6.5 kJ/mol for the phosphazene family, indicating good agreement with experimental values.

Conclusions:

  • The study successfully extended the experimental gas-phase basicity scale into the superbasic region using organic bases.
  • The established scale, now incorporating organic superbases, provides a more accessible platform for future research.
  • Computational methods, specifically DFT, show good predictive power for the gas-phase basicity of phosphazenes.