摘要:

The reaction of methoxide ion with 2-nitro-4-trifluoromethylsulfonylanisole, 4-nitro-2-triftuoromethylsulfonylanisole and 2,4- bis(trifluoromethylsulfonyl)anisole in DMSO has been studied by1H and19F nmr. Evidence for the transient formation ofgem-dimethoxy σ-adducts arising from nucleophilic attack at the aromatic C1 carbon is given. Concurrent methoxide ion attack occurs at the sulfur atom of the SO2CF3group to give the aryl methyl sulfonates ArSO3CH3, which are slowly converted into aryl sulfonates ArSO3−. The1H chemical shifts of the anisoles are consistent with a greater electron-withdrawing effect of the SO2CF3group compared to the nitro group. In contrast, a 4-nitro group appears to be more efficient than a 4-SO2CF3group in delocalizing the negative charge of the σ-adducts.

ISSN:0008-4042    

DOI:10.1139/v80-011

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Primary kinetic isotope effects have been measured for the base-catalyzed exchange reaction of 4′,1″-dimethyl-1,2,3,4-dibenzcyclohepta-1,3-diene-6-one,1. It was found that the isotope effectskH/kTandkD/kTfor the faster exchanging protons (13.6 and 3.8 respectively) are significantly larger than the corresponding values for the slower exchanging protons (4.6 and 1.6 respectively). These differences could result from truly unequal isotope effects due to transition state differences or intrusion of a second pathway for exchange of the less reactive proton in the dedeuteration reaction. The data appear to support the latter interpretation. The secondary deuterium isotope effect was found to be 1.18.

ISSN:0008-4042    

DOI:10.1139/v80-012

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Staqndard free energies of transfer, ΔGt0, of alkali metal chlorides from water to aqueous mixtures of 10, 30, 50, and 70 wt.% glycerol have been determined from emf measurements of the double cell comprising Ag– AgCl and K(Hg) electrodes at 25°C. These values were divided into individual ion contributions by use of tetraphenyl arsonium tetraphenyl boride (Ph4AsBPh4) assumption, the required ΔGt0values of the reference electrolyte (Ph4AsPh4B), obtained by measuring solubilities of KBPh4, Ph4AsPi, and KPi (Pi = picrate) in the solvents. The solvation behaviour of the involved ions, as dictated by their respective ΔGt0(i) values, in this as well as in systems of other similar co-solvents like ethanol, ethylene glycol, and urea, suggests that it is determined by one or several effects of acid-base, Born-type, and dispersion interactions. Moreover, comparable stability of PH4B–, particularly in aqueous glycerol and urea, suggests that "specific interactions" are possibly responsible for the well_known folding-unfolding phenomenon of native conformation of proteins in presence of co-solvent

ISSN:0008-4042    

DOI:10.1139/v80-013

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Rates of detritiation from the C-8 position of various ionized purine molecules have been shown to reflect electrostatic interactions occurring within the transition state of the exchange reaction. The purines are capable of existing as protonated, anionic, neutral, and zwitterionic species in aqueous solution, each of which have been shown previously to undergo specific hydroxide ion-catalyzed detritiation. The effects of substrate charge are quantified as theprotonactivatingfactor,aniondeactivatingfactor, andzwitterionactivatingfactor. Localized charge and not net charge is shown to govern the reactivities of the various species, especially the zwitterions.Estimation of rate constants for the zwitterionic species (hitherto only postulated to account for the observed rate behaviour) has enabled the calculation of the corresponding zwitterionic equilibrium constants (Kzw).Kzwvalues calculated in this manner agree with those estimated from suitable literature pKadata.

ISSN:0008-4042    

DOI:10.1139/v80-014

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Rates of oxygen absorption by styrene (RH) containing 2,2,3,3-tetraphenylbutane and zinc di-isopropyldithiophosphate at 30 °C obey the rate lawwhereRiis the rate of free-radical chain initiation. This order with respect to the styrene concentration implies extensive chain transfer from the poly(peroxystyryl)peroxy radical to a radical derived from the inhibitor. Reaction products confirm the displacement of a di-isopropyldithiophosphoryl radical in the chain termination reaction.Diethyldithiophosphoric acid also inhibits styrene autoxidation by a mechanism which involves extensive chain transfer.

ISSN:0008-4042    

DOI:10.1139/v80-015

出版商:NRC Research Press    

年代:1980

数据来源: NRC