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Related Concept Videos

Structure and Physical Properties of Alkynes02:37

Structure and Physical Properties of Alkynes

Introduction:
In nature, compounds containing both carbon and hydrogen are known as "hydrocarbons". Aliphatic hydrocarbons are compounds whose molecules contain saturated single bonds (i.e., alkanes) or unsaturated double or triple bonds. Alkenes contain carbon–carbon double bonds and have a structural formula CnH2n. Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented by the formula CnH2n-2.
The simplest alkyne is ethyne, or...
Conformations of Ethane and Propane02:18

Conformations of Ethane and Propane

In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered ethane, the...
Acidity of 1-Alkynes02:42

Acidity of 1-Alkynes


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.
Nomenclature of Alkynes02:39

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:
UV–Vis Spectroscopy: Woodward–Fieser Rules01:29

UV–Vis Spectroscopy: Woodward–Fieser Rules

UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...

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First principles potential for the acetylene dimer and refinement by fitting to experiments.

Claude Leforestier1, Adem Tekin, Georg Jansen

  • 1Institut Charles Gerhardt (CTMM)-UMR 5253, CC 1501, Université Montpellier II-CNRS, 34095 Montpellier Cedex 05, France. claude.leforestier@univ-montp2.fr

The Journal of Chemical Physics
|December 24, 2011
PubMed
Summary
This summary is machine-generated.

Researchers developed and refined a new computational model for the acetylene dimer. This refined potential accurately predicts experimental microwave spectra, improving understanding of molecular interactions.

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Area of Science:

  • Computational Chemistry
  • Molecular Spectroscopy
  • Quantum Mechanics

Background:

  • The acetylene dimer is a fundamental system for studying non-covalent interactions.
  • Accurate theoretical potentials are crucial for predicting molecular properties and dynamics.
  • Previous theoretical models showed discrepancies with experimental data for isomerization barriers.

Purpose of the Study:

  • To develop and refine a high-accuracy first-principles potential energy surface for the acetylene dimer.
  • To improve the prediction of the acetylene dimer's microwave spectrum.
  • To accurately model the isomerization pathways and energy barriers within the dimer.

Main Methods:

  • Utilized density functional theory (DFT) combined with symmetry-adapted intermolecular perturbation theory (SAPT) for ab initio calculations.
  • Fitted the calculated interaction energies to a site-site functional form to create a potential model.
  • Refined the potential parameters by fitting to experimental microwave transition frequencies.

Main Results:

  • A new first-principles potential for the acetylene dimer was successfully defined and refined.
  • Initial potential underestimated isomerization barriers, leading to discrepancies with experimental data.
  • Refinement achieved excellent agreement with experimental microwave spectra, within approximately 1 MHz.

Conclusions:

  • The refined potential accurately describes the acetylene dimer's energetics and spectroscopic properties.
  • This work provides a reliable computational tool for studying acetylene dimer dynamics and interactions.
  • The methodology demonstrates the power of combining advanced quantum chemical methods with experimental data for potential development.