Physical imagevsstructure relation: part 12 - structure of 2,2,5,5-tetramethyl-dihydro-furan-3-one oxime and its protonated forms through isomerization and NMR spectra

A Benefit of Using the IDSCRF- over UFF-Radii Cavities and Why Joint Correlations of NMR Chemical Shifts Can Be Advantageous: Condensed Pyridines as an IEF-PCM/GIAO/DFT Case Study

Herein, an advantage of the use of IDSCRF- over UFF-radii-based solute cavities in GIAO/DFT calculations is presented for the ¹³C and especially ¹⁵N NMR chemical shifts made for several bicyclic aromatic nitrogen heterocycles in CDCl₃ solution treated within the classical IEF-PCM solvation scheme. Successful application of the IDSCRF-radii in the non 1:1 joint multinuclear ¹H/¹³C and particularly ¹H/¹³C/¹⁵N correlations of the measured δ_H,C(,N) values to those obtained theoretically is also documented for a series of test systems (-268 ≤ δ_N ≤ -72 ppm). The experimentally yet unknown δ_N's were found in this way for the title compounds via a trinuclear eq 1 determined for an optimally chosen value of the multiplication factor of initial raw δ_H data (m_H = 10). Such a simultaneous analysis of the δ_H,C(,N) data is proposed as a novel method to study the solution structure of the other similar conformationally homogeneous (bio)organic compounds. The issue of small spurious imaginary vibrational frequencies computed for a few molecular systems using the Gaussian 09 default UFF-radii is briefly considered as well.

Multi-conformer molecules in solutions: an NMR-based DFT/MP2 conformational study of two glucopyranosides of a vitamin E model compound

Overall geometries of both glucosyl derivatives of PMC were found on the basis of their NMR spectra in CDCl₃and relatedδ_H,C/ⁿJ_HHIEF-PCM(UFF,CHCl₃)/DFT calculational results.

NMR spectral study of some 2r,6c-diarylpiperidin-4-one (3'-hydroxy-2'-naphthoyl)hydrazones with special reference to γ-syn effect

1H and 13C NMR spectra have been recorded for 2r,6c-diarylpiperidin-4-one (3'-hydroxy-2'-naphthoyl)hydrazones 10-17 and 3,3-dimethyl-2r,6c-bis(p-methoxyphenyl)piperidin-4-one (5). For selected compounds 2D NMR spectra have been recorded. The spectral data along with those reported for related compounds are used to study the effect of a heteroatom X on the 13C chemical shift of a γ-carbon with X Cα Cβ Cγ torsional angle close to 0°, termed as γ-syn effect. Also γ-gauche and δ-effects of the alkyl groups at C-3 on the carbons of the aryl group at C-2 have been studied. The chemical shifts for the naphthalene ring are in accord with the mesomeric and steric effects of the carbonyl and hydroxy groups.

15N chemical shifts of a series of isatin oxime ethers and their corresponding nitrone isomers

In this article, we describe the characteristic (15)N chemical shifts of isatin oxime ethers and their isomer nitrone. These oxime ethers and nitrones are the alkylation reaction products of isatin oximes. In our study, the (15)N chemical shifts observed in these oxime ethers were in the 402-408 (or 22-28) ppm range, although those for their corresponding nitrone series were in the 280-320 (or -100 to -60) ppm range. This remarkable difference in (15)N NMR chemical shift values could potentially be used to determine the O- versus N-alkylation of oximes, even when only one isomer is available. In this paper, the differences in (15)N NMR chemical shifts serve as the basis for a discussion about how to distinguish both regioisomers derived from the oximes alkylation.