摘要:

The kinetics of formation and decomposition of the hydroxyl-σ adduct2derived from 4,6-dinitrobenzofuroxan1have been studied in various water – dimethylsulphoxide (DMSO) – tetramethylammonium chloride (I = 0.5 M) mixtures. At pH < 7, the formation of2occurs exclusively from water attack at the 7-carbon of1. This process is strongly favored by DMSO: the first-order rate constantk1H2O changes from 1.9 × 10−2 s−1in water to 1.33 s−1in 90% DMSO. Taking into account the decrease in the water content of the solutions, and assuming that only one water molecule participates in the reaction, this increase ink1H2O reflects a 103-fold increase in the ability of a water molecule to act as a nucleophile. This interesting result compares well with previous data reported by Murto for the solvolysis of 2,4-dinitrofluorobenzene in the same solvent mixtures.

ISSN:0008-4042    

DOI:10.1139/v80-180

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Newpara-dimethoxyl andpara-diacetoxy derivatives in the naphthalene, anthracene, naphthacene, naphtho (2,3-c) thiophene and benzo-cthiophene series are synthesized via the trapping ofo-quinodimethanes by various dienophiles. Among these compounds, an intermediate for the synthesis of daunomycinone has been prepared and can be oxidized to a benzoquinone which provides access to new analogues of this important antileukemic agent. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v80-181

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A method is described which allows, with a single experiment, the determination of the rate constants of formation and decomposition of bisulfite addition compounds.

ISSN:0008-4042    

DOI:10.1139/v80-182

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The structure of a tricyclic diketone produced during Meyer–Schuster rearrangement has been established by chemical and X-ray crystallographic evidence.

ISSN:0008-4042    

DOI:10.1139/v80-183

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The coupling over seven bonds between19F nuclei and protons inp-methylbenzyl fluoride and a series of ring-substituted derivatives is used to estimate the value for a conformation in which the C—F bond lies in a plane perpendicular to the benzene ring. TheJmethod is then used to show that in CS2solution, the Conformational preference of the fluoromethyl group is very weak in 3,5-dichloro-4-methylbenzyl fluoride and in 3,5-dibromo-4-methylbenzyl fluoride. The barrier to rotation about the exocyclic carbon—carbon bond is perhaps as large as 0.2 kcal/mol. Inp-methylbenzyl fluoride, the C—F bond prefers a plane perpendicular to the benzene plane by ca. 0.9 kcal/mol. Good agreement is found with the Conformational preferences based on couplings over six or seven bonds between the methylene protons and thepararing or methyl protons. The deductions are compared with calculations at various levels of molecular orbital theory.

ISSN:0008-4042    

DOI:10.1139/v80-184

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Cryoscopy was used to determine the low concentration (< 1 molal) stoichiometric molal activity coefficients of: chlorobenzene,m-dichlorobenzene,o-dichlorobenzene, and nitromethane in benzene. The data were corrected to a fixed temperature (10 °C) by using pre-existing heat of mixing data. The activity coefficients all showed negative deviations from Henry's law ideality, and some of the factors that contribute to this non-ideality were discussed.

ISSN:0008-4042    

DOI:10.1139/v80-185

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Suitably blocked carbohydrates containing free thio4, amino5, and hydroxyl10, 19nucleophilic functionalities have been treated with (a) ferrocenecarbonyl chlorides2and3, (b)N,N-dimethylaminomethylferrocene methiodide12, and (c) ferrocenyl tosylate16to form the ferrocenyl sugar derivatives6, 7, 8, 9, 11, 13, 14, 15, and20. Direct conjugation of a free, water-soluble sugar to ferrocene was achieved by the formation of a Schiff's base between glucosamine hydrochloride25and ferrocene carboxaldehyde24. The synthesis of ferrocenyl sugars using bridging group technology is exemplified by the conjugation of the thio sugar4to ferrocene via the versatile coupling reagent cyanuric chloride21to form thes-triazine compound23. These products have been studied by1H nmr spectroscopy: chemical shifts, coupling constants, and proton spin–lattice relaxation measurements.

ISSN:0008-4042    

DOI:10.1139/v80-186

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Acylations of aromatic substrates with ketenes involve the reactivity of species similar to vinyl cations. Resonance stabilization of ketene – aluminum chloride complexes seems to make these complexes less reactive than corresponding vinyl cations.The kinetic isotope effect of the reaction with dimethylketene and benzene is 1.06, compatible with vinylcation cases, but not with acylation with CH3COBF4types of electrophiles.Substrate specificity was determined fromk(toluene)/k(benzene) values. It was 47.2 for dimethylketene and 173.7 for diphenylketene. The diphenylketene – aluminum chloride complex could be isolated.

ISSN:0008-4042    

DOI:10.1139/v80-187

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Nuclear Overhauser effect difference experiments on vitamins D2and D3at 400 MHz allow an unambiguous assignment to be made for the HEand HZprotons bonded to the C-19 carbon. This assignment is especially important since the A ring, and hence the C-19 atom, undergoes a conformational interconversion. The results indicate the importance of proton nOe difference experiments in determining points of configuration and they indicate that the assignment of resonances based on allylic coupling constants in a molecule undergoing a conformational equilibrium can be incorrect.

ISSN:0008-4042    

DOI:10.1139/v80-188

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Carbon-13 chemical shifts of 8 chromones and 35 isoflavones variously substituted by hydroxy-, acetoxy-, and methoxy-groups are assigned. The applicability of chemical shift increments reflecting inductive and resonance effects is discussed. Some general relations between substitution patterns and carbon shielding useful for the identification of naturally occurring isoflavones are outlined. Typical C—H couplings of chromone and phenyl carbons are analyzed for a 4′,6,7-trisubstituted derivative.

ISSN:0008-4042    

DOI:10.1139/v80-189

出版商:NRC Research Press    

年代:1980

数据来源: NRC