Search results for "polycyclic compounds"

17O NMR study of chlorinated anisoles

1988

The 17O NMR chemical shifts of anisole and all 19 chlorinated anisoles measured in CDCI3 at ambient temperature show a dispersion of approximately 40 ppm. The substituent chemical shifts (SCS) of di- or more highly chlorinated compounds cannot be reproduced by addition of single substituent effects. Theoretical calculations of the 17O NMR chemical shifts have been attempted by molecular mechanical and semi-empirical molecular orbital methods at the INDO level, but the results are not satisfactory.

Accumulation of polycyclic aromatic hydrocarbons in cultivated microalgae.

1975

Extending Limits of Chlorine Kinetic Isotope Effects

2012

Chlorine kinetic isotope effects exceeding semiclassical limits were observed in enzyme-catalyzed reactions, but their source has not been yet identified. Herein we show that unusually large chlorine kinetic isotope effects are associated with reactions in which chlorine is the central atom that is being passed between two heavy atoms. The origin of these large values is the ratio of imaginary frequencies for light-to-heavy species (the so-called temperature-independent factor).

Über die Synthese von o-Acylamino-β-dimethylaminopropiophenonen Mitt.: Aminomethylierung von 2-Nitro-5-methoxy-und 2-Nitro-5-benzyloxyacetophenon

1971

Der von Makino und Takahashi sowie Joh als 2-Nitro-5-methoxy-β-dimethylamino-propiophenon bezeichnete Korper wurde als 2-Nitro-5-methoxy-α-dimethylaminomethyl-acrylophenon identifiziert. Nach einer fruher beschriebenen Methode zur Darstellung von 2-Nitro-β-dimethylamino-propiophenon war es moglich, 2-Nitro-5-methoxy- und 2-Nitro-5-benzyloxy-acetophenon normal zu aminomethylieren. –Die Synthese von 2-Amino-5-methoxy-, 2-Amino-5-benzyloxy- und 2-Amino-5-hydroxy-β-dimethylamino-propiophenon sowie ihrer Acetylderivate wird beschrieben. Synthesis of o-Acylamino-β-dimethylamino-propiophenones The compound synthetized by Makino and Takahashi and by Joh described as 2-nitro-5-methoxy-β-dimethylamin…

Using theozymes for designing transition-state analogs for the intramolecular aldol reaction of δ-diketones

2001

Two theozymes for the intramolecular aldol reaction of δ-diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition-state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant …

Enantioselective Synthesis of Unsymmetrical Benzoins from (S)-Mandelic Acid Enolate and Aromatic Aldehydes.

2004

The reaction of the lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with aromatic aldehydes proceeds readily to give the corresponding aldol products in good yields and diastereoselectivities. Subsequent hydroxyl protection, basic hydrolysis of the dioxolanone, oxidative decarboxylation of the α-hydroxyacid moiety, and hydroxyl deprotection provides chiral unsymmetrical benzoins with high enantiomeric excesses.

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.

Chlorine partitioning in the lowermost Arctic vortex during the cold winter 2015/2016

2019

Activated chlorine compounds in the polar winter stratosphere drive catalytic cycles that deplete ozone and methane, whose abundances are highly relevant to the evolution of global climate. The present work introduces a novel dataset of in situ measurements of relevant chlorine species in the lowermost Arctic stratosphere from the aircraft mission POLSTRACC–GW-LCYCLE–SALSA during winter 2015/2016. The major stages of chemical evolution of the lower polar vortex are presented in a consistent series of high-resolution mass spectrometric observations of HCl and ClONO2. Simultaneous measurements of CFC-12 are used to derive total inorganic chlorine (Cly) and active chlorine (ClOx). The new data…

Circular and linear dichroism of aggregates of chlorophyll a and chlorophyll b in 3-methylpentane and paraffin oil.

1996

A circular (CD) and linear dichroism (LD) study of the water adducts of the green plant chlorophylls a (Chl a) and b (Chl b) in hydrocarbon solvents 3-methylpentane and paraffin oil is presented. A strong red shift of the Qy-absorption band from 663 to 746 nm (1678 cm−1) is observed as the water adduct of Chl a is formed. The Chl a-water adduct shows a strong, nonconservative CD signal, which is characterized by a positive peak at 748 nm and two negative peaks at 720 and 771 nm. The maximum CD (AL - AR) is only one order of magnitude smaller than the isotropic absorption maximum. We propose that this exceptionally strong signal is the so-called psi-type CD. The LD spectrum was measured in a…

Horseradish peroxidase-catalyzed oxidation of chlorophyll a with hydrogen peroxide Characterization of the products and mechanism of the reaction

AbstractHorseradish peroxidase was verified to catalyze, without any phenol, the hydrogen peroxide oxidation of chlorophyll a (Chl a), solubilized with Triton X-100. The 132(S) and 132(R) diastereomers of 132-hydroxyChl a were characterized as major oxidation products (ca. 60%) by TLC on sucrose, UV–vis, 1H, and 13C NMR spectra, as well as fast-atom bombardment MS. A minor amount of the 152-methyl, 173-phytyl ester of Mg-unstable chlorin was identified on the basis of its UV–vis spectrum and reactivity with diazomethane, which converted it to the 131,152-dimethyl, 173-phytyl ester of Mg-purpurin 7. The side products (ca. 10%) were suggested to include the 173-phytyl ester of Mg-purpurin 18,…