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Conformation of some biologically active aromatic ureas
Boriana Hadjieva1, Sonia Ilieva, Diana Cheshmedzhieva
1Department of Chemistry, University of Sofia, 1 James Bourchier Avenue, 1164 Sofia, Bulgaria.
Summary
Tri-substituted ureas exist in two trans conformations, identified by distinct N-H stretching frequencies in IR spectroscopy. These conformations, trans I and trans II, are influenced by benzyl and phenyl substituents.
Area of Science:
- Organic Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Tri-substituted ureas are important organic compounds with diverse applications.
- Understanding the conformational preferences of these molecules is crucial for predicting their properties and reactivity.
- Previous studies have explored urea conformations, but specific details for benzyl and phenyl substituted variants require further investigation.
Purpose of the Study:
- To determine the conformational states of tri-substituted ureas with benzyl and/or phenyl substituents.
- To correlate experimental Infrared (IR) spectroscopic data with theoretical computational results.
- To elucidate the structural basis for observed N-H stretching frequencies.
Main Methods:
- Experimental IR spectroscopy was employed to measure N-H stretching mode frequencies.
- Density Functional Theory (DFT) calculations, specifically B3LYP/6-31G(d,p), were performed on selected compounds.
- Analysis of spectral data and computational outputs to identify conformational isomers.
Main Results:
- Two distinct types of N-H bands were observed in the IR spectra, corresponding to different trans conformations.
- A type band (trans I) appeared above 3460 cm⁻¹, characteristic of a classical trans conformation.
- B type band (trans II) was observed between 3430–3420 cm⁻¹, indicating an alternative trans form with intramolecular hydrogen bonding to an aromatic ring.
Conclusions:
- The study provides strong evidence for two stable trans conformations in tri-substituted ureas with aromatic substituents.
- The observed N-H frequencies are reliable indicators of the specific trans conformation (trans I or trans II).
- Intramolecular hydrogen bonding involving the aromatic ring significantly influences the conformational landscape and spectroscopic signatures of these ureas.