Search results for "Effects"

1980

Formation and behaviour of radiation induced free radicals in statistical copolymers from vinyl hydrosulfide and styrene (1:1, 1:4, and 1:10) were investigated by means of ESR spectroscopy. The corresponding homopolymers were also included in these studies. After γ-irradiation of the copolymers at 77 K and subsequent annealing to 293 K it was possible to detect thio radicals. Their relative yields were found to increase with increasing styrene content. Investigations regarding the thermal behaviour of the radiation induced radicals in the copolymers allowed the assumption of two mechanisms responsible for the formation of the thio radicals: First, the formation takes place via ion radicals …

1H, 13C and 15N NMR study of 2-alkylnitrosoamino-4-nitropyridines and N-oxides: An example on restricted inversion of sp3 nitrogen

2007

Abstract The 1 H, 13 C and 15 N NMR chemical shifts of seven 2-alkylnitrosoamino-4-nitropyridines and seven 2-alkylnitrosoamino-4-nitropyridine N -oxides have been assigned. The GIAO/DFT 13 C chemical shifts of energetically optimized structures have been calculated. The results were compared to the chemical shifts of previously studied 2-alkylamino and 2-alkylnitramino derivatives of 4-nitropyridine and 4-nitropyridine N -oxide. In sterically crowded ortho -substituted congener (2-ethylnitrosoamino-3-methyl-4-nitropyridine N -oxide) restricted inversion of pyramidal amino nitrogen forms a chiral center in the molecule and makes the geminal protons of N–CH 2 -moiety diastereotopic. In 5- an…

ortho-Substituent effects inN-arylacetamides. NMR and molecular mechanics investigation

1995

1H, 13C, 15N and 17O NMR spectra of N-phenylacetamide (acetanilide) and 21 ortho-substituted acetanilides were measured and assigned. The observed NMR parameters are related to the Hammett substituent parameters and conformational characteristics of the acetamido moiety estimated by molecular mechanics calculations. Significant relationships were found for the 13C NMR chemical shifts of C-5 (para to substituent) and the direct spin–spin coupling constant, 1J(C, H), of C-3 (ortho to substituent) with Hammett substituent parameters. For 15N NMR chemical shifts of the amido nitrogen, no general correlation with the Hammett substituent parameters was found. The interactions between functionalit…

Substituent effects of1H NMR parameters of chlorinated diphenyl ethers. A statistical approach

1994

The 1H NMR spectra of 64 polychlorinated diphenyl ethers (PCDEs) were measured and assigned. Multiple linear regression analysis was used to estimate the effects of chlorine atoms on the 1H NMR chemical shifts and coupling constants. The ‘simple sum rules’ were found to be inadequate for the prediction of 1H NMR chemical shifts of PCDEs. Therefore, corrective terms of two chlorine atoms were taken into account. The most important effects on chemical shifts were shown to be the steric interactions of two adjacent chlorine atoms and the intramolecular ring current effect observed in the ortho-proton of tri-ortho-substituted PCDEs. The substituent effects on J(HH) coupling constants were found…

Rearrangement products of 3-methanesulfonyl-N-methyl-N-nitroaniline.

2003

Two isomeric products (C 8 H 10 N 2 O 4 S) of the rearrangement of 3-methanesulfonyl-N-methyl-N-nitroaniline have been investigated, viz. 3-methanesulfonyl-N-methyl-2-nitroaniline, which was the main product of the rearrangement, and 5-methanesulfonyl-N-methyl-2-nitroaniline. In both molecules, the aromatic rings are appreciably deformed towards ortho-quinonoidal geometry by electronic and steric interactions. The crystal structure is stabilized, in both cases, by weak C-H...O hydrogen bonds.

Synthesis and Conformational Properties of Nonsymmetric Pillar[5]arenes and Their Acetonitrile Inclusion Compounds

2010

The catalytic cyclocondensation of 1-butoxy-4-methoxy-2,5-bis(methoxymethyl)benzene (1d) affords a statistical mixture of the regioisomeric pillar[5]arenes 3a–d in high yield. The alkoxy groups are arranged stereoselectively in a mode so that they avoid steric interactions. The rotation of the benzene rings is, at room temperature, fast in terms of the NMR timescale and leads to a de facto Cs symmetry for 3a–c and a C5h symmetry for 3d. All four structural isomers can encapsulate two CH3CN guest molecules. The structure determinations are based on four crystal structure analyses (constitutions) and NMR spectroscopic measurements (conformations).

Zinc-salophen complexes as selective receptors for tertiary amines

2007

Zinc-salophen compounds 1-3 incorporating in the given order 1,2-diaminobenzene, 2,3-diaminonaphthalene, and 9,10-diaminophenantrene moieties were synthesised. Their binding properties toward a series of tertiary amines were assessed by UV-Vis and fluorescence spectroscopy in chloroform solution. Unprecedented selectivities of quinuclidine vs. triethylamine higher than 105 were recorded, thereby revealing the dramatic influence of steric effects on axial coordination of tertiary amines. X-Ray diffraction analyses showed that in the solid state compound 2 is dimeric, but its 1 : 1 quinuclidine complex is monomeric. Strong indications were obtained that both free receptors and their amine add…

Synthesis, characterization and kinetics of the metallation of the intermediate compound to produce compound · (H2O) from Rh(II) tetraacetate

1998

Abstract Photochemical irradiation of mixtures of [Rh2(μ-O2CCH3)4]·(HOCH3)2 and P(2-(CH3O)C6H4)Ph2 (POMe) in CH2Cl2 solution (1:1 molar ratio) yields quantitatively compound [ Rh 2 (μ- O 2 CCH 3 ) 3 ( O 2 CCH 3 )(η 2 - P (2-( CH 3 O ) C 6 H 4 ) Ph 2 ]·( H 2 O ) (1) containing a POMe acting as a chelating equatorial ( P ) axial ( O ) donor ligand. This compound undergoes intramolecular CH activation reaction at one of the phenyl rings in CHCl3 or CH3COOH/toluene solution at room temperature to form the monometallated compound [ Rh 2 (μ- O 2 CCH 3 ) 3 (μ-( C C 3 H 4 ) P (2-( CH 3 O C 6 H 4 ) Ph )]· ( H 2 O ) ( 2 ). The kinetics of the 1 → bd2 reaction have been studied in acid media (CH3CO…

Flipping Motion To Bias the Organized Supramolecular Polymerization of N-Heterotriangulenes

2019

Synergistic experimental and theoretical studies have allowed the disentangling of the possible pathways for the supramolecular polymerization of a series of dicyanovinyl-bridged N-heterotriangulene (NHT) derivatives bearing benzamide units with achiral (1a) and chiral (1b,c) side chains. The synthesis of these bowl-shaped, self-assembling units yields a mixture of monomeric species with C3- and C1-symmetry. Both monomeric species are able to self-assemble into different supramolecular aggregates with sufficient stability to coexist in freshly prepared solutions. The dissimilar ratio of the aggregates initially generated results in different spectroscopic features and, more specifically, in…

Structure elucidation of the adducts formed by fjord region Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine.

1999

Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (+/-)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 degrees C for 30 min to give four DB[a, l]PDE-14-N(6)dA adducts: (-)-anti-trans (26%), (+)-anti-trans (26%), (-)-anti-cis (17%), and (+)-anti-cis (17%). The (+/-)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a, l]PDE-14-N(6)dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (-)-syn-cis (19%), (-)-syn-trans (13%), and (+/-)-syn-DB[a,l]PDE-14-N7Ade (22%). T…