¹³C NMR Chemical Shift Calculations for Some Substituted Pyridines:  A Comparative Consideration

Abstract

For three series of mono-, di-, and trisubstituted pyridines, respectively, available incremental methods and calculation programs for estimating the corresponding 13C NMR chemical shifts were employed and compared with the results obtained. The following methods and programs were used for testing them for their accuracy: simple pyridine increments, a simplified increment calculation on the base of benzene increments (program AROSIM , ), the calculation method of Fürst and Pretsch − (Carbon-13 module for ChemWindows), SPECAL from Specinfo (a database founded calculation program), CSPEC2, , gNMR, CNMR, and HyperNMR, respectively.

A one-flask synthesis and characterization of novel symmetrical pyridyl monoselenides and X-ray crystal structure of bis(5-bromo-2-pyridyl) selenide and bis(2-bromo-5-pyridyl) selenide

“…In 13 C NMR spectroscopic data obtained for the three compounds, the order of chemical shifts observed for substituted and unsubstituted carbons of pyridyl ring is in fair agreement with those assigned for the substituted pyridines in literature [32,33]. The assignment of the peaks to each carbon of the prepared molecules is based on the numbering followed for the compounds in Scheme 1.…”

Biodegradation of 7-Hydroxycoumarin in Pseudomonas mandelii 7HK4 via ipso-Hydroxylation of 3-(2,4-Dihydroxyphenyl)-propionic Acid

“…Besides, pyridine aromatic carbons are usually differentiated into two resonances at higher field (C-3/5, meta position) and three at lower field (C-2/6, ortho position; C-4, para position), where the electron-withdrawing effect of nitrogen is effective [ 41 , 42 ]. The chemical shift of 115.22 ppm showed that the analyzed compound had relatively strongly shielded unsubstituted aromatic carbon, which should be in meta -position from nitrogen, in ortho -position from the carbonyl group, and in meta - or para -position from the carboxyl group (C-5 atom), as shown in Figure S14 in the Supplementary Material [ 43 , 44 ]. This led to the conclusion that structure 9 , as shown in Figure 7 , 6-(2-carboxyethyl)-4-oxo-1,4-dihydropyridine-2-carboxylic acid, was formed during incubation of meta -cleavage product of catechol derivative with NH 4 Cl, as depicted in Scheme 1 .…”

Solvent effects on 15N NMR coordination shifts

“…It has therefore been assumed that solvation effects in coordination compounds are largely negligible in comparison with shift alterations upon metal complexation . Consequently, 15 N NMR chemical shifts are acquired, their magnitudes are computationally predicted, and they are interpreted in terms of structure on a regular basis. However, this is performed often without considering any possible solvent effects on δ 15 N. The aforementioned hypothesis became generally accepted although neither solvent effects nor their interplay with the influence of substituents modulating the nitrogen electron density on the magnitude of δ 1 5 N has yet been systematically assessed.…”