摘要:

The value of the rate constantk1for the reaction e−solv → RO−solv + H, [1], at 295 K and 1 bar is ≤1.4 × 105 s−1in methanol and ≤8 × 104 s−1in ethanol. The respective volumes of activation averaged between 1 bar and 2 kbar are ΔV1≠ ≤ −21 and ≤ −22 cm3mol−1. A high concentration of potassium hydroxide (1 M) or water (5 M) decreases the apparent value ofk1somewhat but has little or no effect on the value of ΔV1≠. The effect of pressure on the rate constant of e−solv + S → product, [2], was also measured for a series of solutes that displays a wide range of reactivity. Experimental values of ΔV2≠depend on the relative contributions of the effects of solvent density on the reactant diffusion rates, the concentrations of the actual reacting species, and the relative energies of the reactant and intermediate states. For reactions whose rates are near the diffusion controlled limit,k2 ≈ 1010 M−1s−1in methanol and ethanol, the values of ΔV2≠are positive and similar to those for the diffusion of simple ions. ΔV≠(e−solvdiffusion) = 4 cm3mol−1in methanol and 6 cm3mol−1in ethanol. Cadmium chloride is apparently not completely dissociated in alcohols, andk(e−solv + CdCl2) < k(e−solv + CdCl+) < k(e−solv + Cd2+). For a series of compounds with lower rate constants there is a correlation between logk2and ΔV2≠, the latter being negative for very low values ofk2. The products of electron capture by benzene, toluene, ethyl acetate, and possibly acetonitrile appear to be stabilized by protonation:S−solv + ROH → SH + RO−slov, [4]. The results indicate that the decomposition of e−solvin a pure alcohol occurs by protonation of the electron site, e−solv + ROH → H + RO−slov, [4′], rather than by electron transfer to an alcohol molecule followed by decomposition of the anio

ISSN:0008-4042    

DOI:10.1139/v76-167

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The preparation, properties, and vibrational spectra are reported for the following complexes of lead(II) thiocyanate with mono- and bidentate ligands: Pb(NCS)2•2py, Pb(NCS)2•phen, Pb(NCS)2•2phen, Pb(NCS)2•tmen, Pb(NCS)2•en, Pb(NCS)2•2en, Pb(NCS)2•2dmso, and Pb(NCS)2•2dma. Assignments are made for the ν(CN), ν(CS), and δ(NCS) vibrational bands of the thiocyanate group and the results are discussed in terms of the type of coordination of NCS with lead(II). Values are consistent with bridge-bonded and/or N-bonded thiocyanate. Infrared and Raman spectra of the complexes Pb(NCS)2•bipy and Pb(NCS)2•4tu are reexamined and new assignments are made which support bridge-bonded and/or N-bonded NCS contrary to previous reports of S-bonded NCS.

ISSN:0008-4042    

DOI:10.1139/v76-168

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The electrochemical reduction of 1,3-diketones C6H5—CO—CR1R2—CO—R3(R1 = H, CH3; R2 = CH3, CH2C6H5; R3 = CH3, C6H5) in an hydroorganic medium corresponds to a bielectronic process and leads to 1,2-cyclopropanediols which, in most cases, are obtained in good yields. The polarographic results are presented and the mechanisms are discussed.

ISSN:0008-4042    

DOI:10.1139/v76-169

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Polarographic reduction of two series of benzoylacetanilides has been investigated in 40% (by volume) ethanolic Britton–Robinson buffers. One series (A) contains substituents on the anilide moiety, and the second (B) has substituents on both the anilide and benzoyl moieties. Polarographic controlled-potential electrolysis data indicate that the electroactive species in both series is the protonated form (ArCOCH2CONHAr′)H+. The reduction half-wave potentials of anilides of seriesAwere found to be independent of the nature of the substituent, whereas those of seriesBshow a good linear relationship when plottedvs. the σ substituent constant of the substituent on the benzoyl moiety (ρ = 0.284,r = 0.995). Values of the acid dissociation constants of the keto (K1) and enol (K2) tautomers of the anilides of seriesAwere calculated; unlike theirE1/2values, the pK1data show a linear correlation with the Hammett substituent constant, σ. The pK2values show, however, little variation with σ.

ISSN:0008-4042    

DOI:10.1139/v76-170

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The13C nmr spectra of a series of 50 methyl substituted norbornanols have been determined to gain further insight into the nature of stereochemical effects on the shieldings of carbons having closely neighboring substituents. The relatively rigid norbornyl skeleton permits examination of a variety of orientations of substituents separated by three and four bonds, the γ and δ interactions, respectively. While methyl carbons close to γ substituents exhibit upfield shifts, as is well established, methyl carbons close toδsubstituents are significantly deshielded. Even more striking shifts are found for the carbons bearing these closely lying groups. The penultimate carbons in a fragment having a δ interaction between terminal groups show deviations of up to +11 ppm from the shieldings predicted by simple additivity. For fragments having a corresponding γ interaction, the penultimate carbons absorb as much as −10 ppm from the values expected by additivity. These deviations have considerable potential for stereochemical assignments and offer a challenge for theoretical interpretation.Some norbornenols and the acetates of several of the norbornanols were also included in this series and the latter shieldings are compared briefly with those observed for the parent alcohols.

ISSN:0008-4042    

DOI:10.1139/v76-171

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNisubstitution.

ISSN:0008-4042    

DOI:10.1139/v76-172

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

13C chemical shift data were obtained for amino acids related to glycine which had the following types of substituents on C-2: alkyl, branched chain alkyl, ω-amino alkyl, and ω-guanido alkyl. Such data were obtained for aqueous solutions at a pHbetween the pKvalues of the carboxyl and 2-amino groups (zwitterion form). The data were subjected to graphical and statistical analysis to obtain separate predictive equations for C-1, C-2, and other carbon atoms. Data for the change in chemical shifts on titration with acid were also obtained to aid in13C assignments and to elucidate configuration.

ISSN:0008-4042    

DOI:10.1139/v76-173

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The reactions 2 and 3 have been studied by competitive methods. Use of previous Arrheniusparameters for reaction 2 leads tok3 = 1.3 × 1010exp −[(700 ± 100J)/RT]. Arrhenius parameters of reactions 2 and 3 are compared with those for reactions of other radicals with I2and NO.

ISSN:0008-4042    

DOI:10.1139/v76-174

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The binding of Mn2+to a well characterized fulvic acid sample is reported based on the competition with K+in an ion exchange equilibration. The free energy of binding ofto fulvic acid is only 1–2 kJ/equivalent more favourable than that for K+. This suggests an outer sphere electrostatic structure for the complex. The suggestion is confirmed by observation of minimal change in the presence of fulvic acid of the effect of paramagnetic Mn2+on the nmr spectra of water. The interpretation of nmr spectra is supported by comparison with nmr measurements of Mn2+complexes with simple ligands and contrast with nmr measurements on Fe3+– fulvic acid complexing. The latter is confirmed as inner sphere.

ISSN:0008-4042    

DOI:10.1139/v76-175

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The temperature dependence of the rates of hydrolysis of 2,2-dimethylcyclopropyl bromide, 2,2-cis-vinyl-trans-methylcyclopropyl bromide and 2,2-cis-methyl-trans-vinylcyclopropyl bromide have been determined in water. The temperature coefficient of the enthalpy of activation (ΔCp≠) for these compounds was determined to be −52, −27 and −37 cal deg−1mol−1respectively. The relative rate ratios for hydrolysis of the 2,2-methylvinylcyclopropyl bromides with respect to the appropriate 2-vinylcyclopropyl bromide isomer indicate a considerable progress towards allyl cations at the transition state in contrast to the indications of the ΔCp≠values.The ΔCp≠term for such reactions in water depends to an important degree on the external effects of charge development on water structure but is insensitive to internal electrostatic effects. In the three examples of ΔCp≠reported in this study, all tend to show small external effects in spite of evidence which might suggest larger. The differences in ΔCp≠are attributed to the particular shape and charge distribution of the quasi-ion pair.

ISSN:0008-4042    

DOI:10.1139/v76-176

出版商:NRC Research Press    

年代:1976

数据来源: NRC