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Related Concept Videos

Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

4.1K
Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei...
4.1K
Atomic Radii and Effective Nuclear Charge03:08

Atomic Radii and Effective Nuclear Charge

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The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number and distribution of electrons in their valence shells.
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¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

2.2K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
2.2K
Polyprotic Acids03:38

Polyprotic Acids

34.4K
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:
34.4K
Electron Affinity03:07

Electron Affinity

44.8K
The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).
44.8K
Strong Acid and Base Solutions03:22

Strong Acid and Base Solutions

37.7K
A strong acid is a compound that dissociates completely in an aqueous solution and produces a concentration of hydronium ions equal to the initial concentration of acid. For example, 0.20 M hydrobromic acid will dissociate completely in water and produces 0.20 M of hydronium ions and 0.20 M of bromide ions.
37.7K

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Updated: Mar 29, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
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Proton Affinity Calculations with High Level Methods.

Stein Kolboe1

  • 1inGAP Center for Research Based Innovation, Department of Chemistry, University of Oslo , Blindern, P.O. Box 1033, 0315, Oslo, Norway.

Journal of Chemical Theory and Computation
|November 21, 2015
PubMed
Summary
This summary is machine-generated.

This study accurately computed proton affinities for various organic molecules using advanced computational methods. Findings reveal discrepancies in existing literature values for propene and methylbenzenes, highlighting the need for refined data.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Physical Chemistry

Background:

  • Proton affinity is a fundamental chemical property influencing molecular interactions and reactivity.
  • Accurate proton affinity data is crucial for various chemical applications, including reaction mechanism elucidation and drug design.
  • Existing literature values for some compounds may contain inaccuracies, necessitating re-evaluation.

Purpose of the Study:

  • To accurately calculate proton affinities for a range of organic compounds, from small molecules to polycyclic aromatic hydrocarbons.
  • To compare the performance of several high-accuracy computational methods in determining proton affinities.
  • To identify and correct potential inaccuracies in currently accepted literature proton affinity values.

Main Methods:

  • High-accuracy computational chemistry methods were employed, including W1BD, G4, G3B3, CBS-QB3, and M06-2X.
  • Calculations covered a spectrum of molecules, from simple reference compounds to methylbenzenes, naphthalene, and anthracene.
  • Computed proton affinities were rigorously compared against established reference values.

Main Results:

  • Computed proton affinities generally show excellent agreement with accepted reference values, with notable exceptions.
  • Literature values for propene and methylbenzenes appear to be overestimated by 6-7 kJ/mol and 4-5 kJ/mol, respectively.
  • The G4 and G3B3 methods demonstrated good agreement with the high-level W1BD method.
  • The CBS-QB3 method consistently underestimated proton affinities, with errors increasing for larger molecules.
  • The M06-2X functional showed significant deviations for small molecules like CO and ketene but high accuracy for methylbenzenes.

Conclusions:

  • The study provides highly accurate proton affinity data, refining existing literature values for specific compounds.
  • Computational methods exhibit varying degrees of accuracy, with G4 and G3B3 showing robust performance.
  • The findings underscore the importance of employing appropriate computational tools for reliable chemical property determination.