L. Kania

Estimation of the total range of 1JCC couplings in heterocyclic compounds: pyridines and their N-oxides, the experimental and DFT studies

A very large set of one-bond spin-spin carbon carbon coupling constants, 1J(CC), has been measured for 32 variously mono- and disubstituted pyridine N-oxides and for 14 substituted pyridines. The N-oxides studied were 2-, 3- and 4-monosubstituted isomers, and a series of disubstituted compounds. A variety of substituents has been employed (CH3, COCH3, C5H4NO, CN, F, Br, Cl, OH, OCH3, NH2, N(CH3)2 and NO2), which allowed us to study substituent effects thoroughly. Good linear relationships between 1J(C3C4) in 3- and/or 4-substituted pyridine N-oxides and 1J(CipsoCortho) in benzenes and between 1J(C2C3) in 2- and/or 3-substituted pyridine N-oxides and 1J(CipsoCortho) in benzenes have been found. An analogous linear relationship has been observed between 1J(C3C4) in 3- and/or 4-substituted pyridines and 1J(CipsoCortho) in benzenes. It has been also concluded that, by analogy to 1J(CC) couplings in substituted benzenes, those in pyridines and their N-oxides are the substituent electronegativity dependent. The estimated total range covered by 1J(CC), couplings in substituted compounds varies, in the case of 1J(C2C3) couplings for example, from 25 Hz in 2-lithiopyridine N-oxide to ca. 100 Hz in 2,3-difluoropyridine N-oxide and from 18 Hz in 2-lithiopyridine to 92 Hz in 2,3-difluoropyridine. The DFT calculations have been carried out for the parent compounds and for a set of their 2-lithio, and variously substituted fluoro derivatives. The DFT data reproduced very well the experimental coupling values and revealed that the Fermi contact contribution is the dominating factor which governs the magnitude of the CC coupling across one bond.

Structural increments in UV spectra of conjugated carbonyl compounds: Part I. The α-alkyl substituted enaminones

Abstract The configuration and conformation of a series of α-alkyl-β-monoalkyl- and α-alkyl-β-dialkylamino-α,β-unsaturated carbonyl compounds have been established by means of IR and 1 H NMR spectroscopy. A comparison of the maximum absorption of the S 0 → S 1 (π,π * ) transition of derivatives of related structures yielded the spectral constants characteristic of structural features. These are: Δλ g−Z g−E = 12−17 nm (Δν s−Z s−E = −1320 to −1820 cm −1 , Δλ H-bond intra = 17−22 nm (Δν H-bond intra = −2060 to −2690 cm −1 ), Δλ Z−s−Z α-alk = 13 nm (Δν Z−s−Z α-alk = −1340 cm −1 ) and Δλ N-alk 2 NH-alk = 11 nm (Δν N-alk 2 NH-alk = −1330 cm −1 ). The applicability of the system of spectral increments described for simple enamino aldehydes, ketones and amides has been entirely corroborated.

Analysis of spectral parameters of trans- and cis-silyl substituted 1,2-dihalogenoethenes including one-bond CC spinspin coupling constants across double bonds

Abstract Some trans- and cis-1-trialkylsilyl-1,2-dihalogenoethenes have been synthesized and their13C and1H NMR spectra recorded. The compounds studied readily undergo reversible cis-trans isomerization, the cis isomers being thermodynamically more stable than the trans isomers. The value of3J(SiHα)trans is about twice as large as that of3J(SiHα)cis, and the values of2J(CβHα)trans is about one-tenth that of2J(CβHα)cis and this allows ready assignment of the configuration. The one-bond spin spin coupling constants between the ethylenic carbons depend on the electronegativities of the substituents, trans1J(C C) in most cases being larger than1J(C C)cis.

13C NMR studies on the structure of 5H- and 6H-indolo-[2,3-b]quinolines and the related compounds

Abstract A set of 13 C NMR data which included one-bond spin–spin coupling constants has been obtained for a large series of heteroaromatic compounds. It contains, among others, 6-substituted quinolines, their N -oxides, 2- and 5-methoxyindoles. The results obtained for these basic molecules were compared with those measured for a series of variously substituted 5 H - and 6 H -indolo[2,3- b ]quinolines, which shed new light on the electronic structure of the two latter groups of the compounds.

1 H and 13C NMR studies of 6,11-dimethyl-6H-indolo[2,3-b] quinoline and some of its derivatives

The 1H and 13C NMR spectra of the parent 6,11-dimethyl-6H indolo[2,3-b]quinoline and of its nine 2- and 9- methyl-, methoxy- and fluoro-substituted derivatives have been measured and analysed by the use of cosy, HETCOR, SPT INEPT and selective decoupling experiments. The INADEQUATE experiment was applied to yield the one-bond 13C–13C coupling constants for most of the compounds studied. Proton–proton coupling constants including long-range ones have also been determined. Strong concentration effects on the spectra have been observed for all the compounds studied. In particular, large upheld shifts upon the increase of concentration have been observed for some proton resonances. This has been explained in terms of self association of the compounds.

1H and 13C NMR studies on 5,11-dimethyl-5H-indolo[2,3-b]quinoline and some of its derivatives

Abstract The 1H and 13C NMR spectra of the parent 5-methyl-5H-indolo[2,3b-quinoline] and 5,11-dimethyl-5H-indolo[2,3b]quinoline and nine various methyl, methoxy and fluoro derivatives of the latter have been measured and analysed by the use of COSY, HETCOR, COLOC and selective decoupling experiments. This gave unambiguous assignment of all signals in the spectra studied; proton-proton coupling constants across three, four and five bonds have also been determined. The most interesting result found concerns a very large increase in the shielding of carbon 1 upon introduction of a methyl group at C11. This effect is dramatically enhanced by subsequent substitution with a methoxy group at C2.

Structural increments in UV spectra of conjugated carbonyl compounds: Part II. CNDO/S-CI calculations of electronic spectra of enamino aldehydes, enamino ketones and enamino amides

Abstract The semiempirical molecular orbital CNDO/S-CI spectral parameterization is used in order to evaluate structural increments in UV spectra of a series of β-amino-α,β-un- saturated carbonyl compounds. For most of the compounds, theoretical values of con formational and configurational spectral effects are lower than the experimental ones. It is suggested that a substantial part of the discrepancy is associated with the neglect by the CNDO/S-CI approximation of the changes in the nonbonded interaction energies caused by conformational and configurational isomerizaticns. We show that the applica tion of due corrections based on simple electrostatic and van der Waals interactions according to the Lennard-Jones potentials leads to a good agreement in magnitude and sign between the experimental and theoretical increments.

One-bond 13C–13C couplings in diacetylenes: experimental and theoretical studies

Abstract Carbon-carbon spin-spin coupling constants across one bond have been measured in several mono and dialkyl substituted diacetylenes, in dialkyl substituted tetraacetylene and in trimethylsilyl substituted diacetylene. This provides new examples of the coupling constants across Csp–Csp single bonds, which, so far, have been determined for a very few compounds only. The semi-empirical INDO FPT calculations have been performed for mono substituted diacetylenes with substituents varying along the first row of the Periodical Table. The calculated results revealed that one-bond 13C–13C coupling constants across CC triple bonds with the substituent directly bound to the bond concerned as well as those across the central single CC bond are significantly affected by substituent effects.

Substituent effects in various alkyl derivatives of 9aH-quinolizine-1,2,3,4-tetra-carboxylate studied by 13C NMR spectroscopy and X-ray analysis

The 13C NMR spectra of 22 alkyl-substituted 9aH-quinolizine-1,2,3,4-tetracarboxylates have been obtained and X-ray analyses have been performed for three of them. The chemical shift differences between the parent 9aH-quinolizine and the methyl-substituted compounds can only be interpreted in terms of the usual α and β effects for 8-methyl-9aH-quinolizine. 6-, 7-, 9-, and 9a-methyl substituents cause not only a very large deshielding of the carbon at the position of substitution together with shielding changes at adjacent atoms, but also influence the shieldings of the other carbons in both rings of the compounds under study. The observed changes are interpreted in terms of steric hindrance between the methyl groups of ring B and the ester groups of ring A, and hyperconjugative effects introduced by the methyl groups.

Substituent effects in alkyl-substituted tetramethyl 4H-quinolizine-1,2,3,4-tetracarboxylates studied by 1H NMR spectroscopy

Abstract The analysis of all 1 H resonances and a number of three- and four-bond proton-proton coupling constants provides information on the stereochemistry and the electron distribution in methyl and ethyl derivatives of 4 H -quinolizine-1,2,3,4-tetracarboxylate.