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Related Concept Videos

Lewis Acids and Bases02:16

Lewis Acids and Bases

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This lesson delves into Lewis acids and bases in the context of the octet rule for electron-deficient compounds. Here, the concept is discussed, emphasizing the group 13 elements like boron or aluminium. Since group 13 elements possess three valence electrons, they form trivalent compounds with a sextet of electrons and a vacant orbital for the central atom. Consequently, these electron-deficient compounds accept electrons from other species to complete their octet in a chemical reaction. They...
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Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.1K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
3.1K
Acidity of 1-Alkynes02:42

Acidity of 1-Alkynes

10.1K

The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
10.1K
Exceptions to the Octet Rule02:55

Exceptions to the Octet Rule

30.1K
Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:
30.1K
Polyprotic Acids03:38

Polyprotic Acids

29.6K
Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
29.6K
Acid Halides to Carboxylic Acids: Hydrolysis01:01

Acid Halides to Carboxylic Acids: Hydrolysis

2.9K
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic...
2.9K

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Related Experiment Video

Updated: Sep 30, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy

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A free boratriptycene-type Lewis superacid.

Marcel Henkelmann1, Andreas Omlor2, Michael Bolte1

  • 1Institute of Inorganic Chemistry, Goethe University Frankfurt Max-von-Laue-Straße 7 60438 Frankfurt am Main Germany matthias.wagner@chemie.uni-frankfurt.de.

Chemical Science
|March 14, 2022
PubMed
Summary
This summary is machine-generated.

New ferrocene-based borenium salts exhibit exceptionally strong Lewis acidity due to a unique iron-boron interaction. These potent boron Lewis acids have potential applications in catalysis and materials science.

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Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library
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Area of Science:

  • Organometallic Chemistry
  • Boron Chemistry
  • Ferrocene Derivatives

Background:

  • Ferrocenes are versatile organometallic compounds with unique electronic and structural properties.
  • Boron-based Lewis acids are crucial in catalysis and synthesis, but stronger variants are continuously sought.
  • Pyrazabole-bridged ferrocenes offer a rigid scaffold for incorporating reactive boron centers.

Purpose of the Study:

  • To synthesize novel bicyclic pyrazabole-bridged ferrocenes containing boron hydride groups.
  • To generate and characterize borenium salts from these ferrocene derivatives.
  • To investigate the structural, electronic, and Lewis acidity properties of the resulting borenium salts.

Main Methods:

  • Synthesis of bicyclic pyrazabole-bridged ferrocenes via reaction of a dilithiated ferrocene precursor with pyrazoles and chlorosilanes.
  • Formation of borenium salts by treating the ferrocene derivatives with a strong hydride scavenger, [Ph3C][B(C6F5)4].
  • Structural characterization using X-ray crystallography and spectroscopic analysis (11B NMR).
  • Evaluation of Lewis acidity through experimental (Gutmann-Beckett acceptor number) and theoretical (quantum-chemical calculations) methods.

Main Results:

  • Successful synthesis of pyrazabole-bridged ferrocenes and their corresponding borenium salts.
  • X-ray crystallography revealed a highly distorted borenium cation with a large dip angle (40.6°) and a short Fe⋯B distance (2.365(4) Å).
  • 11B NMR spectroscopy showed a significant upfield shift (23.4 ppm), indicative of strong electronic interaction with the iron center.
  • Quantum-chemical calculations confirmed a direct Fe(3d) → B(2p) donor-acceptor interaction, albeit with a low coupling energy (12 kJ mol-1).
  • Experimental and theoretical assessments demonstrated that the borenium cation is an exceptionally strong boron-based Lewis acid (AN = 111).

Conclusions:

  • The synthesized pyrazabole-bridged ferrocene borenium salts represent a new class of highly reactive Lewis acids.
  • The observed strong Lewis acidity is attributed to a direct, albeit weak, Fe→B interaction, influencing the boron center's electronic structure.
  • These compounds are among the strongest known boron-based Lewis acids, offering potential for advanced catalytic applications.