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Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate
Published on: September 13, 2019
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Picolinic and isonicotinic acids: a Fourier transform microwave spectroscopy study.
Isabel Peña1, Marcelino Varela, Vanina G Franco
1Grupo de Espectroscopia Molecular (GEM), Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Unidad Asociada CSIC, Universidad de Valladolid , 47011 Valladolid, Spain.
The Journal of Physical Chemistry. A
|November 11, 2014
Summary
Researchers studied picolinic and isonicotinic acids using advanced microwave spectroscopy. They identified specific molecular structures and confirmed a crucial hydrogen bond in picolinic acid, revealing insights into their chemical properties.
Area of Science:
- Physical Chemistry
- Molecular Spectroscopy
- Organic Chemistry
Background:
- Picolinic and isonicotinic acids are pyridine carboxylic acids with potential applications in pharmaceuticals and materials science.
- Understanding their molecular structure and intermolecular interactions is key to predicting their properties and reactivity.
- Previous studies have provided limited structural data, particularly regarding conformers and hydrogen bonding.
Purpose of the Study:
- To investigate the molecular structure and conformational preferences of picolinic and isonicotinic acids.
- To identify and characterize specific conformers using high-resolution rotational spectroscopy.
- To elucidate the role of intramolecular hydrogen bonding in stabilizing molecular structures.
Main Methods:
- Broadband chirped pulse (CP-FTMW) and narrowband molecular beam (MB-FTMW) Fourier transform microwave spectroscopies were employed.
- Analysis of rotational spectra to determine molecular parameters such as rotational constants and quadrupole coupling constants.
- High-level computational methods were used to support spectral assignments and structural determination.
Main Results:
- Two conformers (s-cis-I and s-cis-II) of picolinic acid and one conformer of isonicotinic acid were identified.
- Experimental evidence for an O-H···N hydrogen bond in the most stable picolinic acid conformer (s-cis-I) was obtained.
- The rs structure of picolinic acid was determined using isotopically substituted species.
- Mesomeric effects were investigated by comparing nuclear quadrupole coupling constants across isomeric acids.
Conclusions:
- The identified hydrogen bond in picolinic acid significantly stabilizes its structure, compensating for the energetic cost of a trans -COOH configuration.
- Microwave spectroscopy provides precise structural information, including the presence and strength of hydrogen bonds.
- The study offers valuable insights into the electronic structure and intermolecular interactions of pyridine carboxylic acids.
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