Related Experiment Video
Updated: Apr 28, 2026
11:45
Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
7.9K
Substituent effects in trans-p,p'-disubstituted azobenzenes: X-ray structures at 100 K and DFT-calculated structures
Katarzyna Gajda1, Bartosz Zarychta1, Zdzisław Daszkiewicz1
1Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
Summary
Substituents on azobenzene impact benzene ring aromaticity. Electron-donating groups cause ring deformation, while electron-withdrawing groups show normal geometry, confirmed by DFT calculations.
Area of Science:
- Crystallography
- Organic Chemistry
- Computational Chemistry
Background:
- Azobenzenes are versatile organic compounds with tunable electronic properties.
- Substituent effects on molecular geometry and aromaticity are crucial for material design.
Purpose of the Study:
- To determine the crystal and molecular structures of two para-substituted azobenzenes.
- To investigate the influence of electron-donating (-NEt2) and electron-withdrawing (-COOEt) groups on benzene ring aromaticity.
- To analyze geometric changes in crystalline and isolated states using DFT calculations.
Main Methods:
- X-ray crystallography for structure determination.
- Density Functional Theory (DFT) calculations for geometric analysis.
- Harmonic Oscillator Model of Aromaticity (HOMA) index for aromaticity assessment.
Main Results:
- N,N,N',N'-tetraethyl-4,4'-(diazenediyl)dianiline (I) exhibits aromatic ring deformation due to the -NEt2 group's steric and electronic effects.
- Diethyl 4,4'-(diazenediyl)dibenzoate (II) shows normal geometry, lying on a crystallographic inversion center.
- DFT calculations revealed significant changes in N=N-C-C torsion angles between crystalline and isolated states.
- HOMA index indicated a slight decrease in aromaticity for compound (I) and no substantial change for compound (II).
Conclusions:
- The study elucidates the distinct structural impacts of electron-donating and electron-withdrawing substituents on azobenzene derivatives.
- Geometric distortions and altered aromaticity are linked to specific substituent types.
- Computational methods complement crystallographic data, providing a comprehensive understanding of molecular behavior.
![[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)
Related Concept Videos
01:18Directing and Steric Effects in Disubstituted Benzene Derivatives
3.2K
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...
3.2K
01:09Directing Effect of Substituents: meta-Directing Groups
5.0K
Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the...
5.0K
02:37Disubstituted Cyclohexanes: cis-trans Isomerism
10.8K
Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
10.8K
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
1.7K
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...
1.7K
01:14Directing Effect of Substituents: ortho–para-Directing Groups
6.5K
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...
6.5K
01:11Nomenclature of Aromatic Compounds with Multiple Substituents
9.1K
When more than one substituent is present on the benzene ring, the IUPAC nomenclature depends on the number of substituents present.
For disubstituted benzene derivatives, with two groups attached to the benzene ring, three constitutional isomers are possible. For example, consider dimethyl benzene, often called xylene, where the second methyl group can be substituted at the second, third, or fourth carbon. The relative position of the substituents is represented by prefixes ortho, meta, or...
For disubstituted benzene derivatives, with two groups attached to the benzene ring, three constitutional isomers are possible. For example, consider dimethyl benzene, often called xylene, where the second methyl group can be substituted at the second, third, or fourth carbon. The relative position of the substituents is represented by prefixes ortho, meta, or...
9.1K