Gas-Phase UV Spectroscopy of Chemical Intermediates Produced in Solution: Oxidation Reactions of Phenylhydrazines by DDQ

Abstract

In this study, we demonstrated cold gas-phase spectroscopy of chemical intermediates produced in solution. Herein, we combined an electrospray ion source with a Tshaped solution mixer for introducing chemical intermediates in solution into the gas phase. Specifically, the oxidation reaction of 2-(4-nitrophenyl)hydrazinecarboxaldehyde (NHCA) by 2,3dichloro-5,6-dicyano-p-benzoquinone (DDQ) was initiated by mixing the methanol solutions of NHCA and DDQ in the T-shaped mixer, and the chemical species were injected into the vacuum apparatus for ultraviolet photodissociation (UVPD) spectroscopy. A cationic intermediate was strongly observed at m/z 150 in the mass spectrum, and the UVPD spectrum was observed under cold (∼10 K) gas-phase conditions. The UVPD spectrum showed a strong, broad absorption at ∼38,000 cm −1 , accompanied by a relatively weak component at ∼34,000 cm −1 . These spectral patterns can be ascribed to a diazonium cation intermediate, whose existence has been predicted in a previous study. This report indicates that cold gas-phase UV spectroscopy can be a useful method for identifying the structure of chemical intermediates produced in solution.

One-Dimensionally Conjugated Carbocyanine Dyes Isolated under Cold Gas-Phase Conditions: Electronic Spectra and Photochemistry

“…Herein, we have studied their vibronic structures. We simulated the vibronic patterns upon the S 1 –S 0 transitions of 1-I and 1-II by calculating the harmonic FC factors Figure a shows a comparison of the simulated pattern with the experimental spectrum obtained for 1 in the region of 16,000–22,000 cm –1 .…”

“…We performed DFT calculations for compounds 1 and 2 using the Gaussian 16 program package at the ωB97X-D/6-311++G­(d,p) level of theory. The choice of this computational level is based on our recent studies in which the calculations well explain the obtained experimental electronic spectra of a variety of molecules in the cold gas phase. ,, We also performed part of the calculations below by using the M06-2X functional, where the results were essentially the same (Table S1).…”

“…We simulated the vibronic patterns upon the S 1 −S 0 transitions of 1-I and 1-II by calculating the harmonic FC factors. 32 Figure 4a shows a comparison of the simulated pattern with the experimental spectrum obtained for 1 in the region of 16,000−22,000 cm −1 . The simulated bar spectra were convoluted using Gaussian curves with a full width at half-maximum (fwhm) of 90 cm −1 to reproduce the profile of the spectral onset.…”