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Updated: Sep 8, 2025
06:18
Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate
Published on: April 24, 2018
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Complex hyperfine-fine structure overlapping in the microwave spectrum of 3,4-lutidine
Eléonore Antonelli1, Ha Vinh Lam Nguyen1,2
1Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France. lam.nguyen@lisa.ipsl.fr.
Physical Chemistry Chemical Physics : PCCP
|July 16, 2025
Summary
Microwave spectroscopy revealed unique methyl rotation barriers in 3,4-lutidine. The nitrogen atom
Area of Science:
- Molecular spectroscopy
- Quantum chemistry
- Physical organic chemistry
Background:
- 3,4-Lutidine is a pyridine derivative with two methyl groups.
- Internal rotation of methyl groups in aromatic compounds is influenced by steric and electronic factors.
- 14N nuclear quadrupole coupling can provide insights into the electronic environment.
Purpose of the Study:
- To investigate the effects of methyl internal rotations and 14N nuclear quadrupole coupling in 3,4-lutidine.
- To determine the barriers to internal rotation for the meta and para methyl groups.
- To understand the influence of the nitrogen atom on these rotational barriers.
Main Methods:
- Pulsed molecular jet Fourier transform microwave spectroscopy (2.0-20.0 GHz).
- Analysis of rotational transitions, including methyl torsion and 14N hyperfine splittings.
- Quantum chemical calculations (B3LYP-D3BJ/6-311++G(d,p) and MP2/6-311++G(d,p)).
- Fitting of spectral data using the XIAM program.
Main Results:
- 680 microwave transitions were assigned and fitted with high accuracy.
- Methyl internal rotation barriers determined: 510 cm-1 (meta) and 426 cm-1 (para).
- Observed reversal of typical barrier heights in adjacent methyl groups.
Conclusions:
- The nitrogen atom's meta-directing effect significantly influences methyl torsional barriers in 3,4-lutidine.
- A unique interplay of steric and electrostatic effects governs methyl rotation in this molecule.
- Spectroscopic and computational methods provide a comprehensive understanding of molecular dynamics.
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