Search results for "Substituent"

Addition of α-Aminonitriles to α,β-Unsaturated Carbonyl Compounds: A One-Pot Synthesis of Polysubstituted Pyrrolidines.

2003

The vinylogous addition of deprotonated N-alkyl-α-aminonitriles to α,β-unsaturated carbonyl compounds yields cyclic intermediates which can be reduced to form polysubstituted pyrrolidines in a one-pot reaction sequence. Since the cyano substituent is lost in the reduction step, the aminonitriles serve as easily accessible (N-alkylamino)-substituted carbanion equivalents.

H2-Antihistaminika, 7. Mitt. Synthese und H2-antihistaminische Wirkung N,N′-substituierter Thioharnstoffe, Cyanoguanidine und Dithiooxamide

1981

Es wurden N′-substituierte Thioharnstoffe, Cyanoguanidine und Dithiooxamide mit einem 5-Methyl-4-imidazolyl-methylthioethyl-Substituenten dargestellt und auf H2-antihistaminische Wirksamkeit untersucht. H2-Antihistaminics, VII: Synthesis and H2-Antihistaminic Activity of N,N′-Substituted Thioureas, Cyanoguanidines and Dithiooxamides N′-Substituted thioureas, cyanoguanidines and dithiooxamides with a 5-methyl-4-imidazolylmethylthioethyl substituent were prepared and tested for their H2-antihistaminic activity.

Unequivocal determination of isomeric products of reaction between 3-methyl-1-phenyl-2-pyrazoline-4,5-dione and aromatic 1,2-diamines

1999

Abstract Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5-dione with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]-quinoxaline products are distinguished by comparison of their 2D z-gradient selected 1H, 15N HMBC (Heteronuclear Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is recognizable by the cross-peak for CH3(3)-N4 and H5-N4 interactions, indicates substitution in position 6 or 7. The applied method is expected to be useful for structure determinations in other positional isomers.

Predominance of resonance over polar effects on1H,13C and15N NMR substituent chemical shifts inN-arylglycines

1998

13C nuclear magnetic resonance spectra of several podocarpane and cassane diterpenoids

1990

The 13C NMR spectra of several diterpenic derivatives having the podocarpane and cassane skeleton were recorded and interpreted. The most significant effects due to substituent orientation, B/C ring junction stereochemistry and conformational changes are briefly discussed.

The effect of chlorine substituent(s) on the primary loss of a methyl radical from chlorinated veratroles (1,2-dimethoxybenzenes)

1989

Preparation of 5‐bromo‐6‐phenylimidazo[2,1‐b][1,3,4]thiadiazol‐2‐ylamines

2008

The reaction of primary or secondary amines with 2,5-dibromo-6-phenylimidazo[2,1-b][1,3,4]-thiadiazole (5) leads to a chemoselective replacement of the 2-Br substituent. The process represents a convenient route to the corresponding 2-ylamines 7a-d. Hydrazine reacts in an analogous fashion (5 → 7e). The structure determinations are based on an X-ray crystal structure analysis and on one- and two-dimensional NMR measurements.

ChemInform Abstract: Diaryldistyrylpyrazines: Solvatochromic and Acidochromic Fluorophores.

2014

Diaryldimethylpyrazines are the starting materials for the synthesis of C2-symmetric donor- or acceptor-substituted distyrylpyrazines. The optical properties of these cruciform-shaped dyes are dominated by the distyrylpyrazine units; the photophysics is controlled by the styryl substitution, the diaryl substituents on the central pyrazine only having a small effect. Protonation occurs on the pyrazine and/or lateral amines or azines, thereby altering the absorption and emission properties. Hypso- and bathochromism as well as fluorescence quenching depend on the nature of the terminal substituent. This, and a significant positive solvatochromism of the fluorescence, allow optical sensing of t…

Unveiling the Substituent Effects in the Stereochemistry of [3+2] Cycloaddition Reactions of Aryl‐ and Alkyldiazomethylphosphonates with Norbornadien…

2021

Scintillation Measurements at Very High Solute Concentrations; Self Quenching-Structure Correlatios

1968

Abstract Measurements of the relative scintillation yields of some liquid organic systems were carried out with several highly soluble scintillator solutes. Self quenching was observed at high concentrations with some of the solutes, but not with others. The results were correlated with the ability of the solute molecules to come together, in a special configuration, close enough to form an association. A study of the atomic models of the solute molecules showed that those moleculeswith chromophor systems which were non-coplanar, or co-planar but shielded by substituent groups, did not produce self quenching. However, those solute molecules with unprotected co-planar chromophor systems did …