Related Experiment Video
Updated: Mar 24, 2026
08:43
Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
Published on: January 19, 2016
10.9K
Hydrogen-atom attack on phenol and toluene is ortho-directed
Olha Krechkivska1, Callan M Wilcox1, Tyler P Troy2
1School of Chemistry, University of New South Wales, Kensington, NSW 2052, Australia. s.kable@unsw.edu.au.
Physical Chemistry Chemical Physics : PCCP
|March 8, 2016
Summary
Hydrogen atom reactions with phenol and toluene preferentially form ortho isomers due to kinetic factors. This ortho selectivity is expected to persist at higher temperatures, influencing early combustion stages.
Area of Science:
- Chemical Kinetics
- Reaction Dynamics
- Spectroscopy
Background:
- Understanding radical reactions is crucial for combustion chemistry.
- Previous studies established benchmarks for H + benzene reactions.
Purpose of the Study:
- Investigate the reaction products of H + phenol and H/D + toluene.
- Determine the isomeric distribution and conformational preferences of reaction products.
- Elucidate the kinetic and thermodynamic factors governing ortho-isomer selectivity.
Main Methods:
- Supersonic expansion with electric discharge.
- Resonance-enhanced multiphoton ionization (REMPI) spectroscopy.
- Mass spectrometry for product identification (m/z = parent + 1, or parent + 2 amu).
- Theoretical calculations for reaction pathways and energy barriers.
Main Results:
- H + phenol reaction exclusively yields the ortho-hydroxy-cyclohexadienyl radical in syn and anti conformers.
- H/D + toluene reaction exclusively forms the ortho-tolyl radical.
- Ortho isomer preference at 100-200 K is kinetically controlled, with a lower entrance channel barrier.
- Calculations benchmarked against H + benzene reaction.
Conclusions:
- The reaction of H + phenol and H/D + toluene strongly favors the ortho isomer under molecular beam conditions.
- Kinetic control, not thermodynamic stability, dictates ortho selectivity.
- Ortho isomer preference is predicted to continue at elevated temperatures relevant to combustion (200-400 °C).
More Related Videos
Related Concept Videos
00:47Radical Formation: Abstraction
4.5K
The electron of an atom can be abstracted from a compound by a relatively unstable radical to generate a new radical of relatively greater stability. For example, an initiator which forms radicals by homolysis can abstract a suitable species like a hydrogen atom or a halogen atom from a compound to generate a new radical. This ability of radicals to propagate by abstraction is a crucial feature of radical chain reactions.
Even though homolysis produces radicals, it is different from radical...
Even though homolysis produces radicals, it is different from radical...
4.5K
00:54Radical Formation: Homolysis
4.6K
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
4.6K
01:26Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
2.3K
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 reactions,...
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 reactions,...
2.3K
01:02Radical Reactivity: Electrophilic Radicals
2.6K
Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a...
2.6K
01:17Radical Anti-Markovnikov Addition to Alkenes: Mechanism
5.0K
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy...
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy...
5.0K
00:51Radical Formation: Elimination
2.4K
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect...
2.4K