¹H NMR utilization of through‐space effects: III—configuration of oximes and analogous compounds

Abstract

The configurational assignment of 2 and E nitrogen derivatives (>C=N--The configurations of dienic nitriles have been previously assigned from through-space effects affecting proton chemical shifts'. The application of cyclic compounds 1 and 2, obtained from isophorone ( 3 5 5 -trimethyl-2-cyclohexen-l-one), has been demonstrated for this approach. The effect of the electric field is the determining factor in assigning configurational isomers, in both dienic nitriles and ketones. ',2 Our purpose is to extend this methodology to the evaluation of through-space effects on the two isomers of the nitrogen derivatives of ketones corresponding to the general formula ZC=N-Y.The Z and E diastereoisomers in the following series of six isophorone derivatives were therefore synthesized and separated: oxime, 0-methyloxime, dimethylhydrazone, tertbutylimine, N,N,N-trimethylhydrazonium iodide and oxime hydrochloride. RESULTS AND DISCUSSION Configurational assignmentThe value of models 1 and 2 is due mainly to the simplicity of their 'H NMR spectra. The assignment of the H-2, H-3 and H-5 proton signals is straightforward. Only H-4 exhibits a long-range coupling with the ethylenic proton, so that its signal is broader than that of H-6, as already demonstrated for dienic nitriles and ketones.' The NMR chemical shifts obtained for derivatives 1 and 2 are shown in

The influence of oxime stereochemistry in the generation of nitrones from ω-alkenyloximes by cyclization or 1,2-prototropy

“…Oxime stereochemical assignment can be made in a number of ways; by C NMR spectra were taken in CDCl 3 . utilization of through-space effects, 8 by 13 C or 15 N NMR spectra studies, 9 and by examination of J13 C, 1 H coupling constants for aldoximes. 10 In this case assignment was based largely on UV π→π* absorption; (E)-1,2-hydroxyiminoketones are known to exhibit a bathochromic shift when their spectra, recorded in basic solution (MeOH-NaOH), are compared with those measured in neutral solution (MeOH), whereas Z-isomers show no such effect.…”

Axial/equatorial populations in ?-hetero-substituted cyclohexanone Oximes andO-methyl oximes

“…O-methyl oxime ethers. All compounds of these series (17)(18)(19)(20)(21)(22)(23) are novel, except 16, which was described by Denmark and Dappen. 5 The 1 H NMR data for the cis-2,4-oximes are presented in Table 1 and they occur as E isomers only.…”

“…4,6 13 C NMR spectroscopy cis-2,4-Oximes. The 13 C NMR chemical shifts of the cis-2,4-oximes (16)(17)(18)(19)(20)(21)(22)(23) and of 15 are given in Table 5. The assignments for the cis-2,4-oximes were easily made by comparison with the chemical shifts of the corresponding cyclohexanones, 16 except the distinction of the C-5 from the C-6 signal, which was attributed from the assignments of 4-tert-butylcyclohexanone oxime 17 and O-methyl oxime, 12 where the C-5 signal is downfield in relation to C-6.…”

“…The relation between electron density at oxygen and its shielding/deshielding properties can be understood as a result of electric effects. 18,19 In fact, the primary reason for studying both oximes and oxime O-methyl ethers was the expected enhancement of the axial proportions in the ethers due to a better CN / Ł cx orbital interaction.…”

Circular dichroism spectroscopy and DFT calculations in determining absolute configuration and E/Z isomers of conjugated oximes

“…In particular, we want to address finding a reliable, unequivocal, and fast method for distinguishing geometric isomers of oximes. This issue has been studied in the past for both saturated and unsaturated oximes using nuclear magnetic resonance (NMR) and electronic circular dichroism (ECD) spectroscopies . It turns out that versatile analysis of 1 H and 13 C NMR spectra in tandem with extensive calculations of NMR parameters is effective for this purpose .…”