Espectroscopia vibracional e propriedades estruturais das chalconas (3E)-4-[4-(dimetilamina) fenil]but-3-en-2-ona e (3R)-3-(4-clorofenil)-3-hidroxi-1-(2-hidroxifenil)propan-1-ona

Abstract

In this work, a systematic study of the vibrational and structural properties of two chalcones, (3E)-4- [ 4- ( dimethylamino ) phenyl ] but-3-en-2-one, C12H15NO (DMAP) and 3-(4- chlorophenyl ) – 3 – hydroxy – 1 - (2-hydroxyphenyl) propano -1- one, C15H13ClO3 (DIHYDROCHAL), were done. The molecules were synthesized, crystallized and characterized by single crystal X-ray diffraction (XRD), Fourier transform Raman spectroscopy (FT-Raman), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and ultraviolet-visible (UV-Vis) spectroscopy. Theoretical quantum chemistry calculations were performed to obtain data on vibration normal modes, the dipole moment, border molecular orbitals, quantum chemical parameters (HOMO-LUMO, energy gap, ionization energy, electron affinity, chemical potential, among others), molecular electrostatic potential map, Hirshfeld surfaces and theoretical UV-vis spectrum. DMAP chalcone has only one aromatic ring, in contrast to most chalcones which are formed by two aromatic rings. The DMAP crystal, at T = 300 K, presents orthorhombic symmetry and space group P212121 with four molecules per unit cell and structural parameters: a = 6.2440(7) Å, b = 7.3723(8) Å, c = 23.627(3) Å. The crystalline structure of DMAP is stabilized by two short intermolecular contacts, both involving the dimethylamine group. The chalcone DIHYDROCHAL presents a monoclinic crystalline structure at room temperature with space group P21/c with four molecules per unit cell and with the following structural parameters: a = 9.8661(11) Å, b = 5.5235(6) Å, c = 24.930(3) Å and β =94.83°. In the direction of the crystallographic a axis, the molecules are arranged in such a way that they form layers. The crystalline structure of DIHYDROCHAL is stabilized by two intermolecular hydrogen bonds involving chloride and carbonyl (C2-H2...Cl and C8-H8...O1). It is also noted that in the crystallographic direction of the a axis, the molecules are arranged forming layers. Through first principle calculations, it was possible to identify most of the normal modes of vibration of the two chalcones. A study of the vibrational modes of DIHYDROCHAL as a function of hydrostatic pressure was also carried out, with changes in the external modes being observed – low-frequency region – which were interpreted as na indication of the occurrence of a structural phase transition between 0.47 and 0, 82 GPa. From the analysis of some of the internal modes, it was possible to infer that the phase transition involves the A ring, since the frequencies of modes associated with vibrations of atoms in this structure suffer discontinuity in the same pressure range.