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Low Temperature Measurements of Carbon-Carbon Spin-Spin Couplings in s-cis and s-trans Rotamers of Enaminoketones; Comparison with DFT Computations

Bugaj M., Kamieńska-Trela K.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 7

1217-1231

EN

Low temperature 13C INADEQUATE spectra of 4-dimethylamino-but-3-en-2-one 1 and 4-methylamino-but-3-en-2-one 2 revealed J(CC) couplings across one, two and three bonds for the s-transand s-cis conformers of compound 1which exists solely in the trans form, and for the s-trans-s-cis and s-cis-s-cis conformers of the trans isomer of compound 2. A set of CC couplings was also obtained for the cis-s-cis-s-trans isomer of 2. The coupling constants obtained span a range of about 70 Hz, from about 2 Hz observed for the couplings across three bonds to 71 Hz measured for the couplings across the double bonds. Only a slight influence is exerted by the conformation on the couplings across one bond in trans-1 and trans-2. The most significant change is observed upon isomerization of compound 2 to the cis form. This outcome leads to internal hydrogen bond formation and to a decrease in both 1J(C2C3) and 1J(C3C4) coupling values, by 2.7 and 5.1 Hz, respectively. The couplings across two bonds are more sensitive towards changes in the conformation than are those across one bond; 2J(C1C3)'s in the s-trans conformers are significantly larger than those in the s-cis structures. Good agreement is observed between the experimental and B3LYP/6-311++G(2d,p)//B3LYP/6-311++G(2d,p) calculated couplings, and the corresponding linear regression is expressed by the following equation: J(CC)exptl. = [0.94(š 0.01) J(CC)calcd. + 0.62 (š0.71)] š 2.12 Hz.

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Indirect Carbon-Carbon Spin-Spin Couplings in Nitrosobenzenes and Benzene. Experiment and Theory

Biedrzycka Z., Kamieńska-Trela K., Witanowski M.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 7

1195-1207

EN

Dynamically averaged 1J(CC) spin-spin coupling constants in nitrosobenzene, p-substituted (F, Cl, Br, I, Me, NO2, OMe, NMe2) nitrosobenzenes, and o-nitrosotoluene as well as 3J(CC)'s in nitrosobenzene are reported and compared with the literature data on 1J(CC), 2J(CC) and 3J(CC) in benzene. The 1J(CC)'s are shown to span a range of 55.5 through 70.5Hz, and the substituent effects on the constants turn out to be significant, but largely local and almost additive. The effects on the constants seem to augment the coupling with the increasing Pauling's electronegativity of the first atom of the substituent concerned, but complications arise if nitrogenous substituents, NMe2, NO and NO2 are considered. For the first time it is shown that quantum mechanicalDFTcalculations of aromatic carbon-carbon couplings can yield, within a small and random spread, the simplest relationship possible, J(CC)exptl = J(CC)calcd., over a broad range of the couplings, starting from -2.5 Hz for 2J(CC) in benzene, through that of about +8 to +10 Hz for 3J(CC)'s in benzene and nitrosobenzene, up to the span of +55 to +70 Hz for 1J(CC)'s including that of benzene, for a total of 34 individual couplings. This has been attained using the B3PW91/6-311++G(d,p)//B3PW91/6-311++G(d,p) approach, where the same functional-basis set combination was employed for geometry optimizations and for subsequent computations of the couplings. These computations revealed significant effects on the couplings of spatial arrangement of angular substituents with respect to the carbon- carbon bonds within a benzene ring. Attractive potential applications of this combination of experiment and theory are indicated in assessing syn-anti equilibria in disubstituted benzenes, by means of aromatic 1J(CC) couplings.

3

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

Biedrzycka Z., Kamieńska-Trela K.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1637-1648

EN

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.

4

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

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

Polish Journal of Chemistry

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2000

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Vol. 74, nr 11

1599-1608

EN

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.