Theoretical study of the structure and vibrational spectra of the Ci(2) conformation of 18-crown-6.
Optimized geometries of 18-crown-6 (18ce6) were calculated at the HF/6-31G* and B3LYP/6-31G* levels of theory for the D3d, Ci(1) and Ci(2) conformations. At the B3LYP level, the Ci(2) optimized geometry was higher in energy by 23.3 and 18.8 kcal mol(-1) than the Ci(1) and D3d optimized geometries, respectively. Harmonic force field, vibrational frequencies and IR absorption intensities were calculated at the corresponding optimized geometry at the B3LYP level for the Ci(2) conformation. Scaled Ci(2) frequencies were compared with the experimental frequencies of free 18ce6, Ci(1) conformation, and 18ce6-urea complex, Ci(2) conformation. This comparison showed possible misassignments in the fundamental vibrational frequencies of 18ce6.
El-Azhary
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Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt.
Al-Kahtani
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AA
D043844:Crown Ethers; D004988:Ethers, Cyclic / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D013059:Spectrum Analysis, Raman / Q000379:methods
D043844:Crown Ethers; D004988:Ethers, Cyclic; C015762:18-crown-6