Schwingungsspektroskopische Untersuchungen der Wasserstoffbrückendynamik in Alkohol-α-Hydroxyester-Komplexen aus topologischer und chiraler Perspektive

Vibrational spectroscopy of hydrogen bond dynamics in alcohol-α-hydroxy ester complexes from a topological and chiral perspective

by Manuel Lange
Doctoral thesis
Date of Examination:2023-06-15
Date of issue:2024-04-26
Advisor:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Dirk Schwarzer
Referee:Prof. Dr. Ricardo A. Mata
Referee:Dr. Tim Schäfer
Referee:Prof. Dr. Oliver Bünermann
Referee:Prof. Dr. Burkhard Geil
Persistent Address: http://dx.doi.org/10.53846/goediss-10469

 

 

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Abstract

English

The success of an organocatalytic reaction in which the bond between substrate and catalyst is non-covalent, e.g. in the form of a hydrogen bond, is determined by the topology of the hydrogen bond in the prereactive complex. If the reaction is to be enantioselective, the relative chirality of the binding partners also matters. This can lead to chirality induction, where a permanently chiral molecule induces chirality on a transiently chiral or prochiral substrate to form a new stereogenic centre. The challenge is to control both the topology and the process of chirality induction by other non-covalent interactions, such as London dispersion. For this purpose, model systems consisting of the permanently chiral α-hydroxy ester methyl lactate and transiently chiral benzyl alcohol derivatives with an aromatic dispersion center were investigated in this work. The results of linear FTIR and Raman spectroscopy of supersonic jet expansions are compared with the predictions of quantum chemical calculations in order to provide unambiguous statements about the preferred hydrogen bond topology and the tendency to chirality induction. The results are supported by a comparison with the non-chiral methyl glycolate-alcohol complexes. It is shown that the topology can be controlled by suitable chemical substitutions on the hydroxy ester or the alcohol and that a uniform chirality induction takes place in all chiral systems. The influence of London dispersion is relevant for both aspects and can be controlled chemically. In addition, first steps in the investigation of the aggregation behaviour of the natural product piperonal and optimisations of the FTIR setup used are presented.
Keywords: hydrogen bond; chirality; chirality induction; hydrogen bond topology; intermolecular interactions; London dispersion; benzyl alcohol; α-hydroxy ester; FTIR spectroscopy; Raman spectroscopy; supersonic jet expansions; quantum chemical calculations; density functional theory
 
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