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Influence of Substituents on Carbon-carbon Coupling Constants in Substituted Acetylenes

100%

Biedrzycka Z. , Kamieńska-Trela K.

Polish Journal of Chemistry

2003

tom Vol. 77 / nr 11

1637-1648

Indirect spin-spin carbon-carbon coupling constants across a triple bond have been calculated using the DFT method in a large series of substituted acetylenes and compared with those determined experimentally. The DFTcalculated coupling data not only follow the trends observed for the experimental results but also the absolute 1JCC values are very well reproduced (in most cases within several Hz). It has been found that the magnitude of the coupling is strongly dependent on the electronegativity of the first atom of the substituent attached to the triple bond which is described by the equation: 1JXCCY (TOTAL) = 25.9 EXEY + 5.4. The smallest 1JCC coupling calculated for Li2C2 is 31.6 Hz and the largest one for C2F2 420.9 Hz, which reflects the dramatic changes occurring in the electronic structure of the triple bond upon substitution. A rough linear correlation has been found between the ln 1JCC(DFT) and the DFT optimized bond lengths, rCC. Additionally, the couplings across one Csp3-Csp and Csp2(arom)-Csp single bonds and those across two Csp3-CC and Csp2(arom)CC bonds have been derived and discussed.

1H and 13C NMR Studies of 5,6,11-Trimethyl-6H-indolo[2,3-b]quinolinium Methylsulfate and Some of Its Derivatives

80%

Kania L. , Kamieńska-Trela K. , Kaczmarek Ł.

Polish Journal of Chemistry

2000

tom Vol. 74, nr 11

1599-1608

1H and 13C NMR spectra of the parent 5,6,11-trimethyl-6H-indolo[2,3-b]quinolinium methylsulfate and of its nine 2- and 9-methyl-, methoxy- and fluoro-substituted derivatives were measured and assigned from COSY 1H-1H, HETCOR 1H-13C and SPT INEPT experiments. Proton and carbon-13 chemical shifts and long range spin-spin coupling constants (nJHH, n = 3, 4) were considered in terms of the electron density distribution in the indoloquinolinium moiety and compared with the corresponding data obtained earlier for 5,11-dimethyl-5H-and 6,11-dimethyl-6H-indolo[2,3-b]quinoline derivatives. The sensitivity of the proton chemical shifts to the changes in concentration was found for all the compounds studied.