Configurational assignment of carbon, silicon and germanium containing propynal oximes by means of ¹³C¹H, ¹³C¹³C and ¹⁵N¹H spin–spin coupling constants

Abstract

Configurational assignment of five carbon, silicon and germanium containing propynal oximes has been carried out by means of experimental measurements and high-level ab initio calculations of their 13C-1H, 13C-13C and 15N-1H spin-spin coupling constants. The title compounds were shown to exist in the nonequilibrium mixture of E and Z isomers with the energy difference of less than 0.3 kcal/mol calculated at the MP2/6-311G** level.

CH···N and CH···O intramolecular hydrogen bonding effects in the 1H, 13C and 15 N NMR spectra of the configurational isomers of 1‐vinylpyrrole‐2‐carbaldehyde oxime substantiated by DFT calculations

“…It is remarkable that the nitrogen lone pair orientation effect in 1-vinylpyrrole-2-carbaldehyde oxime1 is significantly smaller than that in the other aldoximes. [3,4,7,10] Besides, one can see the dramatic difference between the 2 J(N-2', H-1') coupling constants in the 1-E and the 1-Z isomers. The 2 J(N-2', H-1') coupling constant is by as much as 7 times larger in the absolute size in the 1-Z isomer (Table 4) revealing the variable contribution from nitrogen lone pair to this coupling in the configurational isomers of aldoximes.…”

“…Recently, such an effect was successfully employed to carry out the configurational assignment of the new silicon and germanium containing propynal aldoxime. [10] N-Vinylpyrroles were thoroughly studied from an NMR spectroscopic viewpoint. It was shown that both shielding and spin-spin coupling constants were sensitive to the stereo-orientation of the vinyl group relative to the pyrrole ring.…”

Comparative analysis of 13C shielding constants stereospecificity in the silicon and germanium derivatives of acetylenic aldehyde and ketone oximes based on the 13C NMR spectroscopy and GIAO calculations

“…[12] Also, an unusually large orientational effect of the nitrogen lone pair on the 1 J(C,C) coupling constant (13-16 Hz) was found in these compounds. [11] Further investigation of the 13 C NMR spectra for series of oximes with a heteroaryl substituent discovered that the shielding constants of the double bond carbons (C-2 and C-3, Scheme 1) reveal the same stereospecificity in the configurational isomers as those of the triple bond carbons in the propynal oxime (C-2 and C-3, Scheme 1) [13,14] indicating the common character of the stereospecific effect on the carbon shielding constants in the configurational isomers of the conjugated oximes.…”

“…[11,12] In order to develop an idea about the stereospecificity of the 13 C shielding constants in the oximes having a substituent with triple bond, in this work, the silicon and germanium containing acetylenic ketoximes were synthesized and their 13 C NMR spectra were studied. A comparative analysis of 13 C shielding constants stereospecificity in the acetylenic aldoximes and ketoximes was carried out.…”

“…The chemical shift of the 'aldoxime proton' is larger by 0.6-0.7 ppm in the Z isomer of aldoximes compared with that of the E isomer, [1] whereas the chemical shift of the α-carbon of alkyl substituents with a syn-orientation relative to the oxygen atom is lesser by 4-8 ppm than that with an anti-orientation. [3] Very recently the series of the 3-substituted propynal oximes were synthesized and the stereospecificity of both coupling [11] and shielding constants [12] in their diverse isomers was explored. It was recognized that the shielding constants of the triple bond carbons are highly stereospecific.…”