The proton magnetic resonance spectra of some disubstituted acetophenones

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H-6 is adjacent to the acetyl methyl group whilst the 3,4-disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H-6 proton is adjacent to the carbonyl group.     

18O-isotope effect in 13C nuclear magnetic resonance spectroscopy: 5—Substituent group electronic effects in substituted acetophenones

A series of para- and meta-substituted acetophenones were prepared which were highly labeled with ¹⁸O at the carbonyl function. The natural abundance ¹³C NMR spectra of the compounds were recorded and the ¹⁸O-isotope-induced shifts of the carbonyl carbon were measured in order to determine possible substituent group electronic effects on the ¹⁸O-isotope shift. The isotope shifts were found to be correlated with a number of properties which demonstrate the molecular basis of the isotope shift. Good correlations were obtained for the isotope shift as a function of σ_p⁺, the carbonyl stretching frequency, the carbonyl group bond order, the n→π^**transition of the carbonyl group and the chemical shift of the ipso carbon. In contrast, no correlation was observed between the magnitude of the ¹⁸O-induced isotope shift and the ¹³C chemical shift of the carbonyl carbon. These properties are discussed in connection with the theoretical basis of the isotope shift.     

13C nuclear magnetic resonance studies on some substituted isoxazoles

¹³C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4-substituted 3,5-dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C-5 methyl.     

13C Nuclear magnetic resonance studies of some substituted thiols and thioanisoles

¹³C NMR spectra of thiophenol, 4-nitrothiophenol, 4-X-thioanisole (X = NO₂, NH₂, SH, H) were examined in CDCl₃ solution. Substituent chemical shift values (additivity parameters) for the −SH and −SCH₃ groups are reported.In para-substituted thioanisoles, while the −NH₂ group caused a deshielding and −NO₂ a shielding of SCH₃ carbon resonance, −SH appeared to have had no effect on the carbon resonance.     

Mechanism of the oxidation of some substituted acetophenones byN-Bromosuccinimide in acidic media

The kinetics of the reaction of three substituted acetophenones withN-Bromosuccinimide was studied in perchloric acid media in presence of mercuric acetate. The reactions were found to be zero order with respect toNBS while the order with respect to ketones and [H⁺] was found to be unity. The addition of succinimide mercuric acetate and sodium perchlorate has no effect on the rate of oxidation and the rate increases with the decrease in dielectric constant of the medium. Kinetic investigations have revealed that the order of reactivity ism-nitroacetophenone > p-chloroacetophenone > p-methylacetophenone. TheArrhenius equation has been found to be valid in the temperature range 35–55°. Thermodynamic parameters have been calculated. Mechanistic pathways of the reactions are discussed and a rate equation is derived.Hammett's plot gives a ? value of +0.60 for methyl-aryl-ketones.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Chemical shifts of methyl substituted cis-decahydroquinolines

¹⁵N Chemical shifts of cis-decahydroquinoline, N-methyl-cis-decahydroquinoline, and of 19 methyl substituted NH- and NCH₃-cis-decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature ¹³C NMR spectroscopy.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. N?H proton exchange reactions of urea and substituted ureas

Proton-coupled nitrogen-15 NMR spectra of urea, N-methylurea, N,-N′-dimethylurea, N-methyl-N′-benzylurea and N-phenylurea have been obtained at natural abundance level in neutral, basic and acidic solutions at 25°C. Base-catalyzed N? H proton exchange of the ? NH₂ group of N-methylurea in water was found to be 1.5 times faster than that for the -NH- group, while the corresponding acid-catalyzed exchange is 7.5 times faster. Comparison of urea and N,-N′-dimethylurea in water shows urea to be 10 times faster in base but 2 times slower in acid. The ratio of the base-catalyzed N? H proton exchanges of the two -NH- groups of N-methyl-N′-benzylurea in dimethyl sulfoxide is close to unity, whereas the CH₃NH- group exchanges 4 times faster in acid. Similarly, the C₆H₅NH- group of N-methyl-N′-phenylurea exchanges 50 times faster than the CH₃NH- group in base and about 3 orders of magnitude slower in acid. The results are rationalized by consideration of steric and electronic effects.     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

Structural examination of some polychlorinated 2-phenoxyphenols by 1H and 13C nuclear magnetic resonance

Carbon-13 NMR spectra of some polychlorinated 2-phenoxyphenols have been obtained. The substituent chemical shifts obtained by varying the chlorine substitution pattern of one ring are very similar to those reported for the corresponding diphenyl ethers. Thus, the replacement of a 2-chlorine atom by a hydroxyl group only induces minor shielding changes at the adjacent aryl moiety and the ¹³C chemical shift changes are mainly determined by the preferred conformations governed by the steric demand of the ortho substituents. An ¹H NMR/IR study revealed an equilibrium between intermolecular aggregates and intramolecular OH…π species in the concentration interval 2-0.005 M. Any hydrogen bonding effects on ¹³C NMR shieldings are, therefore, minor compared to shielding variations caused by steric perturbations.     

Covariance nuclear magnetic resonance spectroscopy

Covariance nuclear magnetic resonance (NMR) spectroscopy is introduced, which is a new scheme for establishing nuclear spin correlations from NMR experiments. In this method correlated spin dynamics is directly displayed in terms of a covariance matrix of a series of one-dimensional (1D) spectra. In contrast to two-dimensional (2D) Fourier transform NMR, in a covariance spectrum the spectral resolution along the indirect dimension is determined by the favorable spectral resolution obtainable along the detection dimension, thereby reducing the time-consuming sampling requirement along the indirect dimension. The covariance method neither involves a second Fourier transformation nor does it require separate phase correction or apodization along the indirect dimension. The new scheme is demonstrated for cross-relaxation (NOESY) and J-coupling based magnetization transfer (TOCSY) experiments.     

Shiftless nuclear magnetic resonance spectroscopy

The acquisition and analysis of high resolution one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectra without chemical shift frequencies are described. Many variations of shiftless NMR spectroscopy are feasible. A two-dimensional experiment that correlates the dipole-dipole and dipole-dipole couplings in the model peptide , (15)N labeled N-acetyl-leucine is demonstrated. In addition to the resolution of resonances from individual sites in a single crystal sample, the bond lengths and angles are characterized by the two-dimensional powder pattern obtained from a polycrystalline sample.     

Enantioselective reduction of substituted acetophenones by Aspergillus niger

Fourteen strains of Aspergillus niger were isolated from soil samples. These isolates were evaluated for the reduction of acetophenone to 1-phenylethanol. Among the tested isolates, whole cells of the A. niger EBK-9 isolate were found to be an effective biocatalyst for the enantioselective reduction of acetophenone. Under optimized conditions substituted acetophenones were converted to the corresponding optically active alcohol in up to 99% ee.     

Nuclear magnetic resonance spectra of substituted tetraphenylmethylenediphosphine dioxides

Conclusions We studied nuclear magnetic resonance spectra of substituted dioxides of tetraphenylmethylenediphosphine in a medium of trifluoroacetic acid or chloroform. The chemical shifts measured in chloroform satisfactorily agree with Hammett's . Trifluoroacetic acid levels the effect of substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 419–421, February, 1968.     

Geometrical structures of the azines of substituted acetophenones

Conclusions By drawing on measured values of dipole moments and Kerr constants and a study of vibrational spectra, it has been shown that the molecules of the symmetrical azines of the acetophenones exist as EE forms of the s-trans conformer, the angle of rotation of the azomethylidyne fragments around the N-N bond being 130±5° with the phenyl rings displaced out of the C=N bond planes by 35±5°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1996–1999, September, 1977.     

Identification of some isomeric 3,5-unsymmetrically substituted 1-aroyl-pyrazole derivatives by NMR spectroscopy

The ¹H and ¹³C nmr chemical shifts are used for the structural assignment of isomeric 1-aroyl-4,5-dihydro-5-hydroxy-4,4-dimethyl-1H-pyrazoles 1 unsymmetrically substituted with phenyl or methyl in the 3,5-positions of the pyrazole ring. The ¹H nmr spectra of 1-aroyl- or 1-acetyl-4-methyl-1H-pyrazoles 2 are useful in structure elucidation of unsymmetrically 3- or 5-methyl substituted derivatives.