Hydrogen NMR spectra of pyridazine and pyrazole containing 15N

SummaryThe 15N-NMR spectra of azoles, with natural isotope abundance, have been measured under different experimental conditions, and chemical shifts are reported for imidazoles, pyrazoles, oxazoles, isoxazoles, thiazoles, and isothiazoles. General trends of substituent effects in this heterocyclic series are discussed based on the data of 67 substituted azoles, dihydro-and tetrahydroazoles. "N, 'H spin-coupling constants have been determined from spectra obtained by ['HI 4 I5N polarizationtransfer experiments, i.e. an application of INEPT and DEPT pulse sequences. Two-bond and three-bond coupling constants are fully assigned and are discussed in terms of the specific pathways in azoles. The potential of structural applications of the new data is illustrated for isomeric nitro-imidazoles and highly-substituted pyrazoles, and in the case of ring-chain tautomerism of 2-substituted tetrahydrooxazoles.

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Effect of electron lone‐pairs on nuclear spin–spin coupling constants

Gil

Philipsborn

1989

Magnetic Reson in Chemistry

220

107

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The nature and types of lone-pair effects on nuclear spin coupling constants are reviewed in the context of a localized bond description of molecular electronic structure. Emphasis is placed on the importance of residual delocalization involving the otherwise lone-pair orbital, in terms of which the effect of an X lone-pair, when compared with an isoelectronic Y-H or X-H+ group or with an X-R group, and its orientational dependence can be interpreted. One-, two-and three-bond coupling constants are considered and the importance of lone-pair effects for configurational and conformational information is stressed and illustrated. They also serve for a better understanding of substituent inductive effects on coupling constants.A large collection of illustrative examples are presented, with particular attention paid to couplings involving H, C, N, F and P nuclei, organized in a systematic manner into nine categories. The signs of the lone-pair effects on the reduced coupling constants are found to be independent of the actual nuclei under study in the same category. This is taken as an indication that the electron lone-pairs mainly affect the Fermi contact contribution to the coupling and, accordingly, an interpretation is given in terms of simple sum-over-states models. In addition, symmetry-based relationship are established involving the sign of lone-pair effects in coupling constants between nuclei which are a different number of bonds apart.KEY WORDS NMR Multinuclear spin coupling Lone-pair effects Substituent effects Stereochemistry MO Sum-over-states models Electron delocalization CONTENTS

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Hydrogen NMR spectra of pyridazine and pyrazole containing 15N

Cited by 15 publications

References 25 publications

Properties and Reactions of Thiazole

Properties and Reactions of Thiazole

¹⁵N‐NMR Spectra of Azoles with Two Heteroatoms

Effect of electron lone‐pairs on nuclear spin–spin coupling constants

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Hydrogen NMR spectra of pyridazine and pyrazole containing 15N

Cited by 15 publications

References 25 publications

Properties and Reactions of Thiazole

Properties and Reactions of Thiazole

15N‐NMR Spectra of Azoles with Two Heteroatoms

Effect of electron lone‐pairs on nuclear spin–spin coupling constants

Contact Info

Product

Resources

About

¹⁵N‐NMR Spectra of Azoles with Two Heteroatoms