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Related Concept Videos

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride01:26

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride

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Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation...
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Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

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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...
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Hybridization of Atomic Orbitals II03:35

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sp3d and sp3d 2 Hybridization
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Hydrogen Bonds00:26

Hydrogen Bonds

127.9K
Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
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Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared....
127.9K
Hydrogen Bonds01:04

Hydrogen Bonds

11.2K
A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...
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Electrophilic Addition to Alkynes: Halogenation02:38

Electrophilic Addition to Alkynes: Halogenation

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Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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Sequential Hydrogen Tunneling in o-Tolylmethylene.

Thomas Lohmiller1,2, Sujan K Sarkar3,4, Jörg Tatchen5

  • 1Max-Planck-Institut für Chemische Energiekonversion, 45470, Mülheim an der Ruhr, Germany.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|August 4, 2021
PubMed
Summary

o-Tolylmethylene, a metastable triplet carbene, rearranges via hydrogen atom tunneling. Two conformers rapidly interconvert, with the anti conformer

Keywords:
ENDOR spectroscopycarbeneshydrogen transfermatrix isolationtunneling

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Area of Science:

  • Quantum Chemistry
  • Chemical Kinetics
  • Spectroscopy

Background:

  • o-Tolylmethylene (1) is a metastable triplet carbene.
  • It undergoes rearrangement to o-xylylene (2) via hydrogen atom tunneling.
  • This rearrangement occurs even at very low temperatures (2.7 K).

Purpose of the Study:

  • To investigate the mechanism of the rearrangement of o-tolylmethylene.
  • To identify and characterize different conformers of o-tolylmethylene.
  • To understand the role of quantum tunneling in the rearrangement process.

Main Methods:

  • Electron paramagnetic resonance (EPR) spectroscopy.
  • Electron nuclear double resonance (ENDOR) spectroscopy.
  • Conformer-specific kinetic measurements and quantum chemical calculations.

Main Results:

  • Two conformers of o-tolylmethylene (anti and syn) were identified in noble gas matrices and frozen organic solutions.
  • The rate constants for the rearrangement of anti and syn conformers are similar.
  • Anti and syn conformers rapidly interconvert via quantum tunneling, establishing a rotational pre-equilibrium.
  • The [1,4] H migration from the anti conformer is the rate-limiting step for o-xylylene formation.

Conclusions:

  • The study presents an efficient strategy for investigating tunneling equilibria.
  • Quantum tunneling plays a crucial role in the rearrangement of o-tolylmethylene at low temperatures.
  • The interconversion of conformers via tunneling is faster than the subsequent hydrogen migration.