1
|
Gougoula E, Pfeiffer J, Schnell M, Tambornino F. Rotational conformers and nuclear spin isomers of carbonyl diisothiocyanate. Phys Chem Chem Phys 2024; 26:25678-25687. [PMID: 39351688 DOI: 10.1039/d4cp02226b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/10/2024]
Abstract
Nuclear spin isomers of molecules play a pivotal role in our understanding of quantum mechanics and can have significant implications for various fields. In this work, we report the isolation and characterization of stable nuclear spin isomers as well as conformational isomers of a reactive compound, namely carbonyl diisothiocyanate. It can exist as three rotational conformers, two of which, the syn-syn and syn-anti, were observed in a pulsed supersonic jet by chirped pulse Fourier transform microwave spectroscopy in the 2-12 GHz frequency region. The rotational spectra of two distinct nuclear spin isomers of syn-syn-carbonyl diisothiocyanate, ortho and para, were recorded and analyzed. Experimental molecular rotational parameters for the identified rotational and nuclear spin isomers were determined, including rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants. The two nuclear spin isomers are distinguished by unique hyperfine splitting signatures in their rotational spectra as an outcome of their different nuclear spin states. The relative abundances of the two observed conformers in the gas phase were estimated from the intensity of their rotational transitions. Following detection of singly substituted rare isotopologues of the syn-syn conformer, a partial substitution (rs) structure was determined.
Collapse
Affiliation(s)
- Eva Gougoula
- Deutsches-Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.
| | - Jonathan Pfeiffer
- Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany.
| | - Melanie Schnell
- Deutsches-Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
| | - Frank Tambornino
- Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany.
| |
Collapse
|
2
|
A Scent of Peppermint—A Microwave Spectroscopy Analysis on the Composition of Peppermint Oil. Symmetry (Basel) 2022. [DOI: 10.3390/sym14061262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Essential oils have a vast number of applications in different areas of our daily life. Detailed chiral analysis and structural characterization of their constituents remains an important subject in analytical chemistry. Here, we report on a broadband rotational spectroscopy study of peppermint oil in the frequency range 2–8 GHz. We focus on an unambiguous determination of the excess enantiomers of the oil constituents menthone and isomenthone in the oil by applying chirality-sensitive rotational spectroscopy, the so-called microwave three-wave mixing (M3WM) technique. Additionally, a new menthol conformer, not previously characterized, was experimentally observed, and the gas-phase structures of the two conformers of menthol and menthone were determined experimentally based on the assignment of their 13C-isotopologues in natural abundance.
Collapse
|
3
|
Singh H, Pinacho P, Obenchain DA, Quesada-Moreno MM, Schnell M. The many forms of alpha-methoxy phenylacetic acid in the gas phase: flexibility, internal dynamics, and their intramolecular interactions. Phys Chem Chem Phys 2022; 24:27312-27320. [DOI: 10.1039/d2cp03962a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Five conformers of the flexible molecule alpha-methoxy phenylacetic acid were identified using rotational spectroscopy. The conformational landscape, internal dynamics, and intramolecular interactions were investigated.
Collapse
Affiliation(s)
- Himanshi Singh
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
- Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118 Kiel, Germany
| | - Pablo Pinacho
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Daniel A. Obenchain
- Institut fur Physikalische Chemie, Universität Göttingen, Tammannstr. 6, 37077 Göttingen, Germany
| | - María Mar Quesada-Moreno
- Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada, Spain
| | - Melanie Schnell
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
- Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118 Kiel, Germany
| |
Collapse
|
4
|
Quesada-Moreno MM, Schnell M, Obenchain DA. Rotational analysis of naphthol-aromatic ring complexes stabilized by electrostatic and dispersion interactions. Phys Chem Chem Phys 2021; 24:1598-1609. [PMID: 34942639 DOI: 10.1039/d1cp04337d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
For complexes involving aromatic species, substitution effects can influence the preferred geometry. Using broadband rotational spectroscopy, we report the structures of three naphthol-aromatic ring complexes with different heteroatoms (furan and thiophene) and alkyl groups (2,5-dimethylfuran). The aim was to analyze the influence of the presence of heteroatoms or alkyl groups on the structure of the complex and the kind of intermolecular forces that control it. Face or edge arrangements can take place in these complexes via π-π or O-H⋯O/O-H⋯π interactions, respectively. All the experimentally observed complexes present O-H⋯O/O-H⋯π interactions with the hydroxyl group, with different structures and intermolecular interactions depending on the heteroatom present in the five-membered aromatic rings, yielding different symmetries in the experimental structure. Structures are experimentally identified through the use of planar moments of inertia. Further results from SAPT calculations show that dispersion and electrostatic interactions contribute similarly to the stabilization of all the studied complexes. These new spectroscopic results shed light on the influence of dispersion and hydrogen bonding in molecular aggregation of systems with substituted aromatic residues.
Collapse
Affiliation(s)
| | - Melanie Schnell
- Deutsches Elektronen-Synchrotron DESY, Notkestraβe 85, 22607 Hamburg, Germany.,Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straβe 1, 24118 Kiel, Germany.
| | - Daniel A Obenchain
- Deutsches Elektronen-Synchrotron DESY, Notkestraβe 85, 22607 Hamburg, Germany
| |
Collapse
|
5
|
Lopes Jesus AJ, Fausto R, Reva I. Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix. J Phys Chem A 2021; 125:8215-8229. [PMID: 34506137 DOI: 10.1021/acs.jpca.1c05907] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In this work, monomers of carvacrol (5-isopropyl-2-methylphenol), a natural monoterpene exhibiting wide range bioactivity, were trapped in a cryogenic argon matrix and characterized by infrared spectroscopy, while quantum chemical calculations at the B3LYP and MP2 levels were employed to characterize the conformational landscape of the isolated molecule. Four conformers have been localized on the potential energy surface, and the factors accounting for their relative stability were analyzed. The two most stable conformers of carvacrol, differing in the relative orientation of the isopropyl group and both having the OH group pointing away from the vicinal methyl fragment, were identified in the cryomatrix for the first time. The individual spectral signatures of the two conformers were distinguished based on the change in their relative abundance induced by exposing the matrix to broadband infrared light. Matrix-isolated carvacrol was also irradiated with broadband UV light (λ > 200 nm), which resulted in the cleavage of the OH group. Recombination of the released H atom at the ortho- or para-position of the ring resulted in the formation of alkyl-substituted cyclohexadienones. These were found to undergo subsequent valence and open-ring isomerizations, leading, respectively, to the formation of a Dewar isomer and open-chain conjugated ketenes. Decarbonylation of the photoproducts was also observed for longer irradiation times. A mechanistic analysis of the observed photochemical transformations is presented.
Collapse
Affiliation(s)
- A J Lopes Jesus
- University of Coimbra, CQC, Faculty of Pharmacy, 3004-295 Coimbra, Portugal
| | - Rui Fausto
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Igor Reva
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal.,University of Coimbra, CIEPQPF, Department of Chemical Engineering, 3030-790 Coimbra, Portugal
| |
Collapse
|
6
|
Quesada-Moreno MM, Pinacho P, Pérez C, Šekutor M, Schreiner PR, Schnell M. Do Docking Sites Persist Upon Fluorination? The Diadamantyl Ether-Aromatics Challenge for Rotational Spectroscopy and Theory. Chemistry 2021; 27:6198-6203. [PMID: 33512017 PMCID: PMC8048501 DOI: 10.1002/chem.202100078] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Indexed: 12/28/2022]
Abstract
Fluorinated derivatives of biological molecules have proven to be highly efficient at modifying the biological activity of a given protein through changes in the stability and the kind of docking interactions. These interactions can be hindered or facilitated based on the hydrophilic/hydrophobic character of a particular protein region. Diadamantyl ether (C20H30O) possesses both kinds of docking sites, serving as a good template to model these important contacts with aromatic fluorinated counterparts. In this work, an experimental study on the structures of several complexes between diadamantyl ether and benzene as well as a series of fluorinated benzenes is reported to analyze the effect of H→F substitution on the interaction and structure of the resulting molecular clusters using rotational spectroscopy. All experimentally observed complexes are largely dominated by London dispersion interactions with the hydrogen‐terminated surface areas of diadamantyl ether. Already single substitution of one hydrogen atom with fluorine changes the preferred docking site of the complexes. However, the overall contributions of the different intermolecular interactions are similar for the different complexes, contrary to previous studies focusing on the difference in interactions using fluorinated and non‐fluorinated molecules.
Collapse
Affiliation(s)
| | - Pablo Pinacho
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607, Hamburg, Germany
| | - Cristóbal Pérez
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607, Hamburg, Germany
| | - Marina Šekutor
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392, Giessen, Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392, Giessen, Germany
| | - Melanie Schnell
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607, Hamburg, Germany.,Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118, Kiel, Germany
| |
Collapse
|
7
|
Joyce LA, Schultz DM, Sherer EC, Neill JL, Sonstrom RE, Pate BH. Direct regioisomer analysis of crude reaction mixtures via molecular rotational resonance (MRR) spectroscopy. Chem Sci 2020; 11:6332-6338. [PMID: 32953028 PMCID: PMC7472927 DOI: 10.1039/d0sc01853h] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 05/30/2020] [Indexed: 01/05/2023] Open
Abstract
Direct analyses of crude reaction mixtures have been carried out using molecular rotational resonance (MRR) spectroscopy. Two examples are presented, a demonstration application in photocatalytic CH-arylation as well as generation of an intermediate in a natural product synthesis. In both cases, the reaction can proceed at more than one site, leading to a mixture of regioisomers that can be challenging to distinguish. MRR structural parameters were calculated for the low lying conformers for the desired compounds, and then compared to the experimental spectra of the crude mixtures to confirm the presence of these species. Next, quantitation was performed by comparing experimentally measured line intensities with simulations based on computed values for the magnitude and direction of the molecular dipole moment of each species. This identification and quantification was performed without sample purification and without isolated standards of the compounds of interest. The values obtained for MRR quantitation were in good agreement with the chromatographic values. Finally, previously unknown impurities were discovered within the photocatalytic CH-arylation work. This paper demonstrates the utility of MRR as a reaction characterization tool to simplify analytical workflows.
Collapse
Affiliation(s)
- Leo A Joyce
- Department of Process Research & Development , Merck & Co., Inc. , Rahway , NJ 07065 , USA .
| | - Danielle M Schultz
- Department of Process Research & Development , Merck & Co., Inc. , Rahway , NJ 07065 , USA .
| | - Edward C Sherer
- Department of Computational and Structural Chemistry , Merck & Co., Inc. , Rahway , NJ 07065 , USA
| | - Justin L Neill
- BrightSpec, Inc. , 770 Harris St., Suite 104b , Charlottesville , VA 22904 , USA .
| | - Reilly E Sonstrom
- Department of Chemistry , University of Virginia , McCormick Road , Charlottesville , VA 22904 , USA
| | - Brooks H Pate
- Department of Chemistry , University of Virginia , McCormick Road , Charlottesville , VA 22904 , USA
| |
Collapse
|