Unravelling the configuration of transient ortho-quinone methides by combining microfluidics with gas phase vibrational spectroscopy
| Autor: | Knut R. Asmis, Christoph Schneider, Max Grellmann, Matthias Spanka, Marcel Sickert, Detlev Belder, Maik Pahl, Martin Mayer |
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| Rok vydání: | 2020 |
| Předmět: |
chemistry.chemical_classification
Materials science Double bond 010405 organic chemistry General Physics and Astronomy Infrared spectroscopy 010402 general chemistry 01 natural sciences 0104 chemical sciences Quinone chemistry Dehydration reaction Physical chemistry Density functional theory Ion trap Physical and Theoretical Chemistry Brønsted–Lowry acid–base theory Isomerization |
| Zdroj: | Physical Chemistry Chemical Physics. 22:4610-4616 |
| ISSN: | 1463-9084 1463-9076 |
| DOI: | 10.1039/c9cp06435d |
| Popis: | The alkylidene double bond configuration of transient ortho-quinone methides (o-QMs) is studied by cryogenic ion trap vibrational spectroscopy. To this end, o-QMs are formed from ortho-hydroxy benzhydryl alcohols in a Brønsted acid mediated dehydration reaction on a microfluidic chip reactor and the E/Z isomer ratio is determined by comparing the measured gas phase mid-infrared fingerprints with the predicted harmonic spectra from density functional theory calculations. Control over the stereochemistry is achieved by exploiting steric repulsion interactions between the substituents adjacent to the formal double bond of the o-QMs. Attempts to manipulate the ratio of the E- and Z-isomers by varying the reaction conditions were unsuccessful. This observation suggests a low isomerization barrier and hence shorter equilibration times with respect to the on-chip residence time. The fluxional character of the formal double bond is confirmed in 13C-labelling experiments, which reveal a substantially red-shifted CC stretching frequency characteristic for extended, conjugated π-systems. |
| Databáze: | OpenAIRE |
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