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Expression of hyperconjugative stereoelectronic interactions in borazines.
Chem Commun (Camb)
January 2025
Institute of Organic Chemistry, Faculty of Chemistry, University of Vienna, Währinger Strasse 38, 1090, Vienna, Austria.
This paper discusses hyperconjugative stereoelectronic effects in borazines. A series of alkyl-substituted borazines were synthesized and analysed by NMR spectroscopy and X-ray diffraction. Supported by NBO analyses, the significant decreases in coupling constant for the CH groups adjacent to the boron atoms are consistent with the presence of and interactions.
View Article and Find Full Text PDFCorrelation Between NMR Coupling Constants and σ-Donating Properties of N-Heterocyclic Carbenes and Their Derivatives.
Chemistry
January 2025
LCM, Ecole polytechnique, CNRS, IP Paris, 91128, Palaiseau, France.
Is the J coupling constant for protonated carbene a relevant measure of its σ-donation ability? This paper addresses this question by comparing calculated J values with various experimental and theoretical approaches across a broad spectrum of carbene compounds. We examined Arduengo-type NHCs based on the 2-imidazolylidene scaffold and many other derivatives with modified frameworks, including carbenes with extended, saturated, or conjugated rings, reduced heteroatom stabilization, alternative heteroatoms, permanently charged carbenes, acyclic carbenes, amidocarbenes, and cyclic amino(alkyl/aryl) carbenes, carbodicarbenes and carbodiphosphoranes. Our findings reveal a nuanced relationship between different parameters associated with σ-interaction, such as J, Huynh electronic parameter (HEP), σ-donation from ETS-NOCV, and lone pair energy.
View Article and Find Full Text PDFDFT investigation of coupling constant anomalies in substituted β-lactams.
Magn Reson Chem
August 2024
Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, North Carolina, USA.
β-lactams are a chemically diverse group of molecules with a wide range of biological activities. Having recently observed curious trends in J coupling values in studies on this structural class, we sought to obtain a more comprehensive understanding of these diagnostic NMR parameters, specifically interrogating J, J, and J, to differentiate 3- and 4-monosubstituted β-lactams. Further investigation using computational chemistry methods was employed to explore the geometric and electronic origins for the observed and calculated differences between the two substitution patterns.
View Article and Find Full Text PDFDiscovery of Terminal Oxazole-Bearing Natural Products by a Targeted Metabologenomic Approach.
Angew Chem Int Ed Engl
May 2024
Natural Products Research Institute, College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea.
A targeted metabologenomic method was developed to selectively discover terminal oxazole-bearing natural products from bacteria. For this, genes encoding oxazole cyclase, a key enzyme in terminal oxazole biosynthesis, were chosen as the genomic signature to screen bacterial strains that may produce oxazole-bearing compounds. Sixteen strains were identified from the screening of a bacterial DNA library (1,000 strains) using oxazole cyclase gene-targeting polymerase chain reaction (PCR) primers.
View Article and Find Full Text PDFA Versatile Broadband Attached Proton Test Experiment for Routine C Nuclear Magnetic Resonance Spectroscopy.
Molecules
February 2024
Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
The proposed broadband attached proton test sequence allows the user to easily record C nuclear magnetic resonance multiplicity-edited and quaternary-carbon-only spectra. Compared to earlier attached proton test experiments, it preserves both a tolerance for wide ranges of one-bond-coupling constant values and the effective suppression of residual CHn signals in the quaternary-carbon-only spectra. The recording of edited spectra or quaternary-carbon-only spectra is made easy by a single, user-controllable constant.
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