摘要:

The newly determinedHA, scale of acidity has been tested against ionization ratio data for 33 amides. Twenty-nine of these compounds give logIvs.HAslopes of 0.9–1.1 and most are within 0.95–1.05. The average slope for these is 1.001 ± 0.051. TheHAfunction is thus considered to be generally applicable to the ionization of this type of base, and the significance of previously reported amide pKvalues is discussed in the light of these results. Previously reported basicity – substituent constant relations have been reexamined using thermodynamically significant pKdata and earlier conclusions confirmed. Appropriate equations are derived in an attempt to explain the rate–acidity dependence of amide hydrolysis directly in terms of the water activity of the reaction medium. The picture of the hydrolysis transition state which results is in accord with that obtained using methods described by other workers.

ISSN:0008-4042    

DOI:10.1139/v65-069

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v65-070

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

Some commercially available aromatic acids have been treated with sodium azide using a mixture of trifluoroacetic acid and trifluoroacetic anhydride as the reaction medium. Benzoic, ortho-, meta-, and para-toluic, ortho-bromo-, and ortho-nitro-benzoic acids were converted to corresponding N-substituted trifluoroacetamides in good yields. 1-Naphthoic acid was converted to N-(1-naphthyl)-trifluoroacetamide in near quantitative yield. Meta- and para-bromobenzoic and meta- and para-nitrobenzoic acids did not undergo this modified Schmidt reaction under these conditions. The conversion of aromatic acids to N-substituted trifluoroacetamides is discussed and evidence is presented for the mechanism.

ISSN:0008-4042    

DOI:10.1139/v65-071

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The effect of various reagents on the rate of hydrolysis ofn-propyl chlorosulfate in 10 Maqueous dioxane is reported. Halide ions increase the rate of reaction (I− > Br− > Cl−) but perchlorate is without effect. Hydroxide and pyrrolidine have a strong accelerating effect, but only at higher concentrations. These observations support a bimolecular mechanism: rate-determining displacement by nucleophile on carbon, with OSO2Cl−as the leaving group. The present results are not in accord with a previous proposal that alkyl chlorosulfates react by rate-determining sulfur–chlorine bond fission followed by fast displacement by nucleophile on carbon.

ISSN:0008-4042    

DOI:10.1139/v65-072

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The solvolysis of the series of alkyl chlorosulfates, ROSO2Cl, where R = methyl, ethyl,n-propyl, isobutyl, and neopentyl, has been studied in 10 Maqueous dioxane. The relative reactivities fit well a solvolytic mechanism involving displacement by water on carbon, with OSO2Cl as the leaving group. The change in mechanism of solvolysis from bimolecular with the straight-chain chlorosulfates to unimolecular with neopentyl chlorosulfate is shown by the absence of the lyate ion effect and the observation of rearrangement in the latter case.The entropies of activation in chlorosulfate solvolysis appear to be abnormally large. It is proposed that the abnormal ΔS≠indicates a transition state in which both carbon–oxygen and sulfur–chlorine bond weakening occurs. It is shown that some other solvolytic reactions that are characterized by abnormally high entropies of activation may be interpreted on the basis of multiple bond fission (fragmentation). The mechanism of SNireactions is considered in this context.

ISSN:0008-4042    

DOI:10.1139/v65-073

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

At low pressures and elevated temperatures cyclopentyl radicals are found to dissociate mainly by two modes of reaction: about 34% by loss of H atom to form cyclopentene, and about 66% by a C—C bond rupture to form ethylene and allyl radicals. Under the conditions employed no evidence for a third possible mode, the loss of H2to form cyclopentenyl radical, could be found. It is estimated that an incidence of 2% of the latter could have been detected.

ISSN:0008-4042    

DOI:10.1139/v65-074

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The specific rate constant for opening the cyclopentyl radical has been determined to be 1014.5exp –37 700/RT s−1. The energy of activation indicates that any eclipsed pairs of H atoms in the cyclic radical are not de-eclipsed in the activated complex. No evidence for the resulting five-membered linear radical can be found, only evidence for its breakdown products, allyl radical and ethylene.The disproportionation/combination ratio for methyl and cyclopentyl radicals is about 0.3. The energy of activation for methyl abstracting a hydrogen atom from cyclopentane has been confirmed as about 9.5 kcal/mole.Cyclopentyl radical also loses a hydrogen atom to form cyclopentene. The kinetic parameters are difficult to obtain because of radical–radical reactions which form cyclopentene. An analysis of the results indicates an energy of activation at least equal to that for opening the cyclopentyl ring.Evidence is presented to support the view that the cyclopentyl radical loses a molecule of hydrogen to form the resonance-stablized cyclopentenyl radical with an energy of activation close to that for opening the ring, and a pre-exponential factor about 1/10 of that for the opening of the ring.

ISSN:0008-4042    

DOI:10.1139/v65-075

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The fractionation of13C between CO2(g) and CO3−--HCO3−(aq) in solution has been studied in single stage experiments using carbonic anhydrase to catalyze the hydration of CO2. Added metal ions, pH of the equilibrium mixture, and temperature are found to play important roles in the overall fractionation process. Theoretical evaluation of the13CO2(g)--12CO3−(aq) equilibrium constant (K2) has been made using the most recent spectroscopic data on the exchanging species. The variation of the equilibrium constantK2with temperature has been calculated for each 25 deg interval from 0 to 975 °C with the help of the McMaster University IBM 7040 computer. It is shown that the overall13C fractionation in the system may be treated as contributions due mainly to three exchange equilibria whereby13CO2(g) independently exchanges with12CO2(aq), H12CO3(aq),and12CO3−(aq), the corresponding equilibrium constants beingK0,K1, andK2respectively. The best fit values for the equilibrium constants areK0 = 1.0009,K1 = 1.0077, andK2 ≥ 1.013, indicating the orderK0 < K1 < K2.

ISSN:0008-4042    

DOI:10.1139/v65-076

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The 15.1 Mc/s13C n.m.r. spectra of 34 α,β.-unsaturated carbonyl compounds have been obtained and the chemical shifts of the olefinic and carbonyl carbon nuclei are reported. Examples were drawn from the acyclic and five- and six-membered ring alicyclic series. A few aldehydes are included although most of the compounds are ketones. In the case of compounds assumed to be planar, variations of the olefinic shieldings with alkyl substitution parallel those observed previously for olefinic hydrocarbons. The key factor governing the chemical shifts of the carbonyl-carbon nuclei appears to be the extent of conjugation in a given system. Consequently, the13C results provide evidence for steric interference to coplanarity in the hindered systems. This approach is compared with other methods of estimating the extent of steric inhibition of conjugation and its merits are assessed.

ISSN:0008-4042    

DOI:10.1139/v65-077

出版商:NRC Research Press    

年代:1965

数据来源: NRC

摘要:

The constitution of the alkylphosphine – carbon disulfide adducts has been investigated by the study of their infrared spectra. Certain definite features of the spectra of the adducts are the shift of the P—C asymmetric vibrations to higher frequencies and the large shifts in the fundamentals of the acceptor molecule. These features are attributed to the formation of a quadruply connected phosphorus compound. From a comparison of the spectra of the carbon disulfide adducts with those of the corresponding phosphonium compounds, phosphine oxides and phosphines, evidence is provided for the structure of these compounds which has been suggested to be of the phosphonium type.

ISSN:0008-4042    

DOI:10.1139/v65-078

出版商:NRC Research Press    

年代:1965

数据来源: NRC