Abstract
In this work, the structural and vibrational properties of 1-5-(difluoromethyl-1H-pyrrol-2-yl-) ethanone (DFPE) were studied by using the hybrid B3LYP/6-31G* method. The properties were analyzed and compared with those obtained for 1-(1H-pyrrol-2-yl) ethanone (PE) and 1-(5-(trifluoromethyl)-1H-pyrrol-2-yl) ethanone (TFPE). The theoretical 1H-NMR, 13C-NMR and 19F-NMR chemical shifts for DFPE were predicted by using the B3LYP/6-311++G** approach with the GIAO and CGST methods showing the three spectra good concordances with the corresponding experimental ones. A complete assignment of the vibrational spectra was presented.
Highlights
The difluoromethyl group (CF2H) is normally used in areas as pharmacology and medicine because it has hydrogen bond donor properties of great importance in the drug design [1]
We have studied from theoretical point of view the structure, the vibrational spectra and the structural properties of 1-5-(difluoromethyl-1H-pyrrol-2yl-)ethanone (DFPE), a new fluoro methylated-pyrrol derivative synthesized by Fujiwara et al [1] by using zinc difluoro methyl sulfonate salt (ZnDFMS) as reagent and a unreported synthetic procedure
The hydrogen bond donor properties for the CF2H group of DFPE were analyzed by means of the molecular electrostatic potentials [20,21,22,23] and later, they were compared with those obtained for the same group of ZnDFMS [3] and 5-difluoromethyl-1,3,4- thiadiazole-2-amino [4] and, for those obtained in this work for 1-(1H-pyrrol-2-yl) ethanone (PE) and 1-(5-(trifluoromethyl)-1H-pyrrol-2-yl) ethanone (TFPE) [24,25]
Summary
The difluoromethyl group (CF2H) is normally used in areas as pharmacology and medicine because it has hydrogen bond donor properties of great importance in the drug design [1]. Müller et al [10] have reported that the F atom can improve binding efficacy and selectivity of pharmaceuticals products because the fluorination of molecules often imparts desirable properties, such as the metabolic and thermal stability [11,12] In these contexts, the knowing of the structures of compounds containing both, difluoromethyl and pyrrol groups are useful and necessary to predict their properties and behaviours in the different media in which they are involved and, to perform the complete assignments of the corresponding vibrational spectra. For DFPE, three stable structures with C1 symmetries were found in the potential energy surface by using the hybrid B3LYP/6-31G* method which are observed in the Figure 1 together with the numbering of all the atoms These structures were initially modelled with the Gauss View 5.0 program [31] and, they were optimized by using the Gaussian 09 program package [32]. The results for DFPE were compared with those obtained for PE and TFPE
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