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Related Concept Videos

¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
Molecular Orbital Theory II03:51

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams
¹H NMR of Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Bond Dissociation Energy and Activation Energy02:13

Bond Dissociation Energy and Activation Energy

Bond energy is the energy required to break a bond homolytically. These values are usually expressed in units of kcal/mol or kJ/mol and are referred to as bond dissociation energies when given for specific bonds or average bond energies when indicated for a given type of bond over many compounds. Firstly, the bond dissociation energy for a single bond is weaker than that of a double bond, which in turn is weaker than that of a triple bond. Secondly, hydrogen forms relatively strong bonds with...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...

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Measuring Biomolecular DSC Profiles with Thermolabile Ligands to Rapidly Characterize Folding and Binding Interactions
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Roaming dynamics in formaldehyde-d2 dissociation.

Vasiliy Goncharov1, Sridhar A Lahankar, John D Farnum

  • 1Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.

The Journal of Physical Chemistry. A
|September 25, 2009
PubMed
Summary
This summary is machine-generated.

State-resolved photodissociation of deuterated formaldehyde (D2CO) reveals two distinct energy release pathways. These findings clarify the dissociation dynamics and energy partitioning in molecular photolysis.

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Area of Science:

  • Chemical Physics
  • Molecular Dynamics
  • Photochemistry

Background:

  • Understanding molecular photodissociation is crucial for chemical reaction dynamics.
  • Previous studies on H2CO suggested dual dissociation pathways, including a novel

Purpose of the Study:

  • Investigate the state-resolved photodissociation dynamics of deuterated formaldehyde (D2CO).
  • Determine the energy partitioning into molecular photofragments.
  • Compare dissociation pathways between H2CO and D2CO photolysis.

Main Methods:

  • Experimental study of D2CO photodissociation.
  • Theoretical calculations of dissociation dynamics.
  • Analysis of energy distribution in CO and D2 fragments.

Main Results:

  • Observed a clear bimodal energy distribution in molecular photofragments.
  • Identified two distinct dissociation pathways, similar to H2CO.
  • Found correlations between CO rotational levels and D2 vibrational excitation.

Conclusions:

  • The bimodal energy distribution in D2CO photolysis arises from two pathways: conventional transition state and roaming.
  • Energy partitioning differs between H2CO and D2CO, influenced by isotopic substitution.
  • Confirms the roaming mechanism's role in formaldehyde photodissociation.