A comparative analysis of the UV/Visabsorption spectra of nitrobenzaldehydesElectronic supplementary information (ESI) available: Full assignment (including molecular orbitals) of the MS-CASPT2/CASSCF and CC2 vertical spectra. See DOI: 10.1039/c0cp01372b

• Main Authors: Leyva, Verónica, Corral, Inés, Schmierer, Thomas, Gilch, Peter, González, Leticia
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c0cp01372b

In a joint experimental and theoretical study, the UV/Visabsorption spectra of the three isomers ( ortho , meta , para ) of nitrobenzaldehyde (NBA) were analyzed. Absorption spectra are reported for NBA vapors, cyclohexane and acetonitrile solutions. All spectra are poor in vibronic structure and hardly affected in shape by the surroundings (vapor or solution). Moderate solvatochromic shifts of ∼−0.2 eV are measured. For all isomers vertical transition energies, oscillator strengths, and excited state dipole moments were computed using the MS-CASPT2/CASSCF and CC2 methods. Based on these calculations the experimental transitions were assigned. The spectra of all isomers are characterized by weak ( max 100 M −1 cm −1 ) transitions around 350 nm (3.6 eV), arising from nπ* absorptions starting from the lone pairs of the nitro and aldehyde moieties. The next band of intermediate intensity peaking around 300 nm (4.2 eV, max 1000 M −1 cm −1 ) is dominated by ππ* excitations within the arene function. Finally, strong absorptions ( max 10 000 M −1 cm −1 ) were observed around 250 nm (5.0 eV) which we ascribe to ππ* excitations involving the nitro and benzenegroups. UV/Vis absorption spectra of o -, m -, and p -nitrobenzaldehyde have been recorded and assigned with ab initio calculations.