Synthesis, crystal structure, conformational and vibrational properties of 6-acetyl-2,2-dimethyl-chromane

Abstract

The 6-acetyl-2,2-dimethyl-chromane compound was synthesized and characterized by IR, Raman, UV-Visible and 1H NMR spectroscopies. Its solid state structure was determined by X-ray diffraction methods. The substance crystallizes in the triclinic P-1 space group with a = 5.9622(5) Å, b = 10.342(1) Å, c = 10.464(1) Å, α = 63.81(1)°, β = 81.923(9)°, γ = 82.645(9)°, and Z = 2 molecules per unit cell. Due to extended π-bonding delocalization a substantial skeletal fragment of the molecule is planar. The vibrational modes were calculated at B3LYP/6-31G(d,p) level and all of them assigned in the IR and Raman spectra. The DFT calculated 1H NMR spectrum (chemical shifts) were in good agreement with the experimental data. The electronic (UV-Visible) spectrum was calculated using TD-DFT method in gas phase and it was correlated with the experimental data. The assignment and analysis of the frontier HOMO and LUMO orbitals indicate that the absorption bands are mainly originated from π → π* transitions. According to DSC measurements the substance presents a melting point of 93 ºC and decomposes at temperatures higher than 196 ºC.