Related Experiment Video
Updated: Jan 11, 2026
06:48
CD Spectroscopy to Study DNA-Protein Interactions
Published on: February 10, 2022
7.5K
Conformer-selective photoelectron circular dichroism: Experimental development and application to nitrogen chirality.
Etienne Rouquet, Julien Vincent1, Valéria Lepère1
1Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Université Paris-Saclay, F-91405 Orsay, France.
Structural Dynamics (Melville, N.Y.)
|November 10, 2025
Summary
Researchers developed new experimental methods for analyzing flexible molecules, achieving conformer selectivity. These techniques successfully differentiated conformers of 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM), revealing subtle differences in their properties.
Area of Science:
- Physical Chemistry
- Molecular Spectroscopy
- Quantum Chemistry
Background:
- Conformational isomerism in flexible molecules presents challenges for selective analysis.
- Photoelectron Circular Dichroism (PECD) is a sensitive technique for probing molecular chirality.
- Resonance-enhanced multiphoton ionization (REMPI) offers pathways for selective ionization.
Purpose of the Study:
- To present upgraded experimental methods for conformer-selective photoelectron spectroscopy.
- To investigate the photoelectron spectrum, anisotropy parameter, and PECD of jet-cooled flexible molecules.
- To apply these methods to differentiate conformers of 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM).
Main Methods:
- Utilized a one-color resonance-enhanced multiphoton ionization (REMPI) process.
- Employed selective ionization of S0-S1 transitions for conformer differentiation.
- Detailed experimental setup, data acquisition, and processing for accuracy.
Main Results:
- Successfully achieved conformer selectivity in analyzing THIQM.
- Observed slight differences in ionization energies between THIQM conformers (THIQMI and THIQMII).
- PECD spectra showed differences in shape and magnitude, while the anisotropy parameter proved more sensitive to conformational isomerism.
Conclusions:
- The developed experimental scheme enables conformer-selective analysis of flexible molecules.
- The anisotropy parameter is a highly sensitive probe of conformational differences in THIQM.
- This approach advances the study of chiral molecules and their conformers.
Related Concept Videos
02:30Chirality at Nitrogen, Phosphorus, and Sulfur
6.8K
Chirality is most prevalent in carbon-based tetrahedral compounds, but this important facet of molecular symmetry extends to sp3-hybridized nitrogen, phosphorus and sulfur centers, including trivalent molecules with lone pairs. Here, the lone pair behaves as a functional group in addition to the other three substituents to form an analogous tetrahedral center that can be chiral.
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...
6.8K
02:30Chirality in Nature
16.5K
Chirality is the most intriguing yet essential facet of nature, governing life’s biochemical processes and precision. It can be observed from a snail shell pattern in a macroscopic world to an amino acid, the minutest building block of life. Most of the snails around the world have right-coiled shells because of the intrinsic chirality in their genes. All the amino acids present in the human body exist in an enantiomerically pure state, except for glycine - the sole achiral amino acid.
16.5K
01:26Photochemical Electrocyclic Reactions: Stereochemistry
2.2K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
2.2K
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
1.2K
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
1.2K
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
1.7K
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
1.7K
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
1.8K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.8K