OH NO! - Investigating the microsolvation of aminoxyl radicals via FTIR spectroscopy

by Elisabeth Katharina Maria Mercedes Sennert
Doctoral thesis
Date of Examination:2025-09-29
Date of issue:2025-12-02
Advisor:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Marina Bennati
Persistent Address: http://dx.doi.org/10.53846/goediss-11651

 

 

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Abstract

English

This work investigates complexes of stable organic radicals with halogenated alcohols using FTIR jet spectroscopy combined with quantum chemical calculations. Due to the formation of a hydrogen bond, the OH stretching vibration of the alcohol serves as a sensitive probe for the presence of a specific heterodimer (1:1) conformation in the supersonic expansion. The TEMPO (2,2,6,6-tetramethylpiperidinyloxyl) radical is combined with benzyl alcohol and its halogenated derivatives, which are investigated separately beforehand. Two main conformer types are identified, differing in the orientation of the alcohol relative to the radical. The preferred conformer can be controlled in subtle ways by introducing halogens of different sizes (F, Cl, Br, I) and at different positions to the aromatic system of benzyl alcohol. This variation of the alcohol reveals how the interplay between hydrogen bonding and dispersion forces affects the complex stability. The amount of dispersion interaction is quantified using local energy decomposition. Switching to the TEMPO derivative TEMPONE (4-oxo-TEMPO) shows that the additional carbonyl group can act as a hydrogen bond acceptor, competing with the radical NO side. Due to the chiral nature of TEMPONE, relative chirality becomes relevant for the complexes with the transiently chiral benzyl alcohol.
Keywords: FTIR spectroscopy; supersonic expansion; vibrational spectroscopy; hydrogen bonding; alcohols; radicals; dispersion; quantum chemical calculations
 
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