Related Experiment Video
Updated: May 13, 2026
07:06
Continuous Flow Chemistry: Reaction of Diphenyldiazomethane with p-Nitrobenzoic Acid
Published on: November 15, 2017
Unidirectional vibrational energy flow in nitrobenzene.
Brandt C Pein1, Yuxiao Sun, Dana D Dlott
1School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
The Journal of Physical Chemistry. A
|February 26, 2013
Summary
Vibrational energy transfer in nitrobenzene was studied using IR pump-Raman probe. Energy flowed weakly from the phenyl to the nitro group, but not vice versa, impacting energetic materials design.
Area of Science:
- Physical Chemistry
- Molecular Spectroscopy
- Computational Chemistry
Background:
- Understanding molecular vibrations is key to controlling chemical reactions.
- Nitrobenzene serves as a model system for studying energy flow in aromatic compounds.
Purpose of the Study:
- To investigate the directionality of vibrational energy transfer between the nitro and phenyl groups in nitrobenzene.
- To explore the potential for designing molecules with specific energy transfer properties for applications in molecular electronics and phononics.
Main Methods:
- Utilized the IR pump, Raman probe technique to selectively excite vibrational modes.
- Employed quantum chemical calculations to categorize nitrobenzene's normal modes (phenyl, nitro, global).
- Investigated energy transfer dynamics by analyzing vibrational amplitude changes after selective excitation.
Main Results:
- Excitation of nitro group modes showed no detectable energy transfer to the phenyl group.
- Excitation of phenyl group modes resulted in weak energy transfer to global modes, including phenyl-nitro stretching, indicating some amplitude transfer to the nitro group.
- Demonstrated absent energy transfer from nitro to phenyl, but weak transfer from phenyl to nitro.
Conclusions:
- Vibrational energy transfer in nitrobenzene is anisotropic, with limited flow from phenyl to nitro groups.
- The vibrational isolation of the nitro group suggests unique reaction pathways in energetic materials.
- The methodology provides a framework for studying intramolecular vibrational energy flow, aiding in the design of novel functional molecules.
Related Concept Videos
01:37NMR Spectroscopy of Benzene Derivatives
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 constants depend...
00:52¹H 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...
01:20Electrophilic Aromatic Substitution: Nitration of Benzene
The nitration of benzene is an example of an electrophilic aromatic substitution reaction. It involves the formation of a very powerful electrophile, the nitronium ion, which is linear in shape. The reaction occurs through the interaction of two strong acids, sulfuric and nitric acid.
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
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 annulenes. In...
01:18Structure of Benzene: Molecular Orbital Model
According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...