Modulating the Roaming Dynamics for the NO Release in ortho-Nitrobenzenes
Namitha Brijit Bejoy1, Prahlad Roy Chowdhury1, G Naresh Patwari1
1Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
The Journal of Physical Chemistry Letters
|March 13, 2023
Summary
Intramolecular hydrogen bonding in nitroaromatic compounds dictates nitric oxide (NO) release dynamics. Substituents influence NO elimination channels and favor specific dissociation mechanisms like roaming.
Area of Science:
- Physical Chemistry
- Chemical Dynamics
- Photochemistry
Background:
- Nitroaromatic compounds are crucial in various chemical processes.
- Understanding nitric oxide (NO) release is key to controlling chemical reactions.
Purpose of the Study:
- To investigate the influence of ortho-substituents on NO release dynamics during nitroaromatic photodissociation.
- To elucidate the role of intramolecular hydrogen bonding and triplet state potential energy surfaces in NO elimination pathways.
Main Methods:
- Photodissociation experiments of nitroaromatic compounds.
- Analysis of translational energy distributions of NO photofragments.
- Computational modeling of potential energy surfaces and reaction mechanisms.
Main Results:
- A bimodal translational energy distribution of NO fragments indicates two distinct elimination channels (slow and fast).
- The ratio of slow-to-fast NO release is directly correlated with the hydrogen bonding ability of ortho-substituents ([OH > NH2 > CH3 > OCH3]).
- Triplet state potential energy surface topology influences dissociation pathways, favoring roaming mechanisms with hydrogen-bonding substituents.
Conclusions:
- Intramolecular hydrogen bonding significantly regulates NO release dynamics in nitroaromatic photodissociation.
- The interplay between substituent properties, hydrogen bonding, and triplet state topology governs the NO elimination mechanism, including roaming pathways.
More Related Videos
13:21Detection of Nitric Oxide and Superoxide Radical Anion by Electron Paramagnetic Resonance Spectroscopy from Cells using Spin Traps
Published on: August 18, 2012
19.1K
08:17Practical Aspects of Sample Preparation and Setup of 1H R1ρ Relaxation Dispersion Experiments of RNA
Published on: July 9, 2021
4.8K
Related Concept Videos
01:13meta-Directing Deactivators: –NO2, –CN, –CHO, –CO2R, –COR, –CO2H
5.7K
All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
5.7K
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
6.2K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
6.2K
01:14Directing Effect of Substituents: ortho–para-Directing Groups
6.7K
Ortho–para directors are substituent groups attached to the benzene ring and direct the addition of an electrophile to the positions ortho or para to the substituent. All electron-donating groups are considered ortho–para directors. They donate electrons to the ring and make the ring more electron-rich. The ring is therefore susceptible to the addition of electrophiles. Substituents such as amino, hydroxy, or alkoxy, containing lone pairs on the atom adjacent to the ring, donate...
6.7K
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
1.2K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.2K
01:34NMR Spectroscopy of Benzene Derivatives
8.6K
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling...
8.6K
01:18Directing and Steric Effects in Disubstituted Benzene Derivatives
3.1K
When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the...
3.1K