Structural, vibrational spectra and normal coordinate analysis for two tautomers of 4(5)‐(2′‐furyl)‐imidazole

Abstract

We have synthesized both the 4 and 5 tautomeric forms of 4(5)-(2 -furyl)-imidazole (1) and investigated their molecular vibrations by infrared and Raman spectroscopies as well as by calculation based on the density functional theory (DFT) approach. Examination of the temperature dependence of IR intensity revealed the band characteristics of the 4 and 5 tautomers of (1). Comparison of experimental and calculated chemical shifts in nuclear magnetic resonance (NMR) spectroscopy was made in order to identify the two tautomeric forms. The assignment of vibrational normal modes was performed, and the force field obtained reproduced the experimental vibrational wavenumbers with a root mean-square deviation (RMSD) value of ca. 13 cm −1 for both tautomers. The natural bond orbital (NBO) study reveals the characteristics of the electronic delocalization of the two tautomeric structures.

Quantum Mechanical Modeling of Fluoromethylated-pyrrol Derivatives a Study on their Reactivities, Structures and Vibrational Properties

“…A comparison of the theoretical 1 H-NMR, 13 C-NMR, 19 F-NMR chemical shifts for the three conformers of DFPE, calculated employing the GIAO and CGST methods [27,28] at the B3LYP/6-311++G** level, with the corresponding experimental values by means of the root mean square deviations (RMSD) values can be seen in Table 2. In general, the calculated chemical shifts with both methods show higher values than the corresponding experimental ones, as also was observed in other molecules [4,[50][51][52][53][54]. In both cases, the results show a good concordance for the H nuclei with rmsd values between 0.8 and 0.9ppm and a slightly lower agreement for the 13 C nuclei (4.9-4.1 ppm) while the calculated 19 F chemical shifts show the higher rmsd values using the GIAO method (18.2 and 20.8 ppm) and the lower values using the CGST method.…”

“…Additionally, the proximities between the values for the three conformers suggest their presence in solution. A further observation is that the peak belonging to the H atom of the N-H bond appears in furyl compounds at 11.37 ppm [50][51][52][53], in this case for the N5-H6 bonds are observed at 6.88 ppm, as in the 2-(2'-furyl)-1H-imidazole compound [52,53] whose crystalline structure is polymeric with N-H---N bonds. Thus, the small shifts of these peaks towards lower fields suggest for DFPE probably the existence of some intermolecular interaction between nonbonding electrons.…”

“…The experimental bands observed in the infrared spectra in solid phase for DFPE and TFPE were taken from [1] and [24] and they are compared with the corresponding calculated wavenumbers in Table 3. The complete vibrational assignments of the experimental bands to the normal vibration modes were performed by comparison with related molecules [3,4,[20][21][22]42,[49][50][51][52][53][54][55] and taking into account the calculations performed here. The PED contributions for the three DFPE conformers can be seen in Tables S9-S11 while for TFPE are observed in Table S12.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part V

“…Ledesma et al . synthesized both the 4 and 5 tautomeric forms of 4(5)‐(2′‐furyl)imidazole and investigated their molecular vibrations by IR and Raman measurements and DFT calculations . The molecular structure and conformational properties of ethyl trifluoroacetate, CF 3 CO 2 CH 2 CH 3 , were determined in the gas phase by electron diffraction and IR and Raman spectroscopy .…”

Structural and Vibrational Properties and NMR Characterization of (2’-furyl)-Imidazole Compounds

“…Recently, the theoretical and experimental studies on structure, electronic and vibrational properties for the (2'-furyl)-imidazole series were reported by us 13,14,15,16,17 .…”