The Hydrates of TEMPO: Water Vibrations Reveal Radical Microsolvation

Abstract

An organic radical monohydrate complex is detected in vacuum isolation at low temperature by FTIR supersonic jet spectroscopy for the first time. It is shown to exhibit a rich conformational and vibrational coupling dynamics, which can be drastically reduced by appropriate isotope substitution. Its detection with a new gas recycling infrared spectrometer demonstrates the thermal metastability of the gaseous TEMPO radical even under humid gas conditions. Compared to its almost isoelectronic and isostructural, closed shell ketone analogue, the hydrogen bond of the solvating water is found to be less directional, but stronger and more strongly downshifting the bonded water OH stretch vibration. A second solvent water directs the first one into a metastable hydrogen bond position to solvate the nitrogen center and the first water at the same time.

Raising the benchmark potential of a simple alcohol-ketone intermolecular balance

“…S15 and S16 in the ESI †) and MEK case (see Fig. S10-13 in ESI †) and in analogous cases 52 . For the small MEK signal D = O ?…”

Connections between the accuracy of rotational constants and equilibrium molecular structures

“…On the other hand, advancements in gasphase spectroscopic techniques have extended their use to larger and flexible systems (such as clusters [30][31][32] , amino acids 33,34 , DNA-scaffold ribosugars 35 ) as well as to unstable species (obtained by flash vacuum pyrolysis 36,37 or discharge 38 ). Increasingly, complicated spectra have to be analyzed which strongly require theory for their interpretation 12,13,34,36,[39][40][41] . For isolated systems, rotational spectroscopy can serve to demonstrate the accuracy that can be reached by quantum chemistry and to show how much we need to push theory to obtain predictions useful to experiment.…”

Investigation of Intermolecular Ketone-Alcohol Balances via FTIR Spectroscopy

“…Also, trimers in ketone-water balances were previously observed in the same spectral region. [171] In contrast, evidence for the small signal D = O ? being some higher complex is not entirely conclusive, even though concentration series with MeOH (see Fig.…”