摘要:

The proton and19F high resolution nuclear magnetic resonance spectra of benzenesulfonyl fluoride and of some derivatives are analyzed to yield spin–spin coupling constants between19F and the ring protons. These parameters display a marked dependence on the ring substituents and it is not clear how their conformational behaviour can be distinguished from intrinsic substituent perturbations. The large magnitudes of the couplings over six bonds to theparaprotons, relative to those in benzoyl fluoride, strongly indicate the importance of conformations in which the S—F bond does not lie in the benzene plane. The methyl group replacement technique suggests that the six-bond coupling contains contributions in addition to that from a σ–π mechanism. The chemical shift of theparaproton yields a π electron density at the contiguous carbon atom which is considerably smaller than in nitrobenzene, for example. The19F shifts are much less sensitive toorthosubstituents than are the19F shifts in benzoyl fluoride derivatives, implying much smaller intramolecular van der Waals interactions in the sulfonyl compounds.

ISSN:0008-4042    

DOI:10.1139/v78-278

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

TheJmethod, depending on a comparison between observed spin–spin coupling constants over six bonds between protons on a side chain andpararing protons and those calculated by a hindered rotor treatment, is applied to the determination of the twofold barrier to internal rotation about the carbon–carbon bonds in 3,5-dichlorobenzyl alcohol and selenol. In the alcohol, the C—O bond prefers the benzene plane by 0.3 ± 0.2 kcal/mol whereas, in the selenol, the C—Se bond prefers a plane perpendicular to the benzene ring by 3.8 ± 0.7 kcal/mol. Comparison with the thiol suggests that a major component of the barrier arises from repulsive interactions, increasing as the size of the XH (X = O, S, Se) group increases.

ISSN:0008-4042    

DOI:10.1139/v78-279

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The adduct (4a) of 1,4-dimethyl-2,3-diphenylcyclopentadiene with dimethyl azodicarboxylate is isomerized by one or more equivalents of trifiuoroacetic acid to the exocyclic alkene5a. The di-tert-butyl analogue4bis isomerized by limited amounts of trifluoroacetic acid to a mixture of5band the oxadiazine10, the latter being the only product with 1 equiv. of acid;5bcan be made more efficiently from4bby the action of pyridine or triethylamine. Excess acid converts4b,5b, or10to the oxadiazinone7. A protonated intermediate derived from4bis postulated as the precursor to both5band7in acid, a view supported by deuterium labelling studies.

ISSN:0008-4042    

DOI:10.1139/v78-280

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A new extraction–spectrophotometric method has been developed for the determination of trace amounts of phosphorus as orthophosphate. The method is based on the chemistry of 12-tungstophosphoric acid, H3PW12O40(TPA). In the procedure, orthophosphate is converted quantitatively to TPA in aqueous solution at a tungstate–phosphate molar ratio ≥24, in the pHrange 1.2 to 1.9 and in the temperature range 60 to 100 °C. The TPA is subsequently extracted inton-amyl alcohol and its absorbance measured at 267 nm. Beer's law is followed up to at least 25 µg/ml P. The method is less prone to solution conditions and species interference (especially As(V) and Si(IV)) than the widely used molybdenum-blue methods and is competitive in terms of sensitivity, precision, and accuracy. The TPA method was applied successfully to the determination of phosphate in a variety of phosphorus-containing specimens including natural waters, ores, and alloys.Based on potentiometric and spectrophotometric studies, a scheme which accounts for the observed heptaproticity of TPA is proposed.

ISSN:0008-4042    

DOI:10.1139/v78-281

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Various equations which have been proposed to provide the 'best' functional form for the dependence of rate upon pressure for reactions in solution have been tested for the extraction of ΔV≠and dΔV≠/dpfor the hydrolysis of benzyl chloride at 30 °C and at pressures over the range 1 to 6895 bar. One hundred individual rate constants were determined for this reaction at pressure increments of 345 bar and provide a sufficiently large body of data to permit application of statistical methods for testing the various rate–pressure functions with little risk of bias.

ISSN:0008-4042    

DOI:10.1139/v78-282

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Mössbauer data are reported for a number of heterocyclic compounds containing tellurium. The influence on the Mössbauer parameters of the constraints imposed by accommodating tellurium in these ring systems are discussed. The influence of the bulky aryl ligand 2-biphenylyl, C12H9—, on the Mössbauer parameters of diaryltellurium dihalides and aryltellurium trihalides has also been investigated.

ISSN:0008-4042    

DOI:10.1139/v78-283

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A synthesis of methyl pentopyranosid-4-uloses bas been achieved by microbiological oxidation byAcetobacter suboxydansof some methyl pentopyranosides. The oxidation products were isolated as theirO-methyloxime derivatives, and the assignment of the configuration of the oximes was made on the basis of the carbon-13 magnetic resonance spectra. An analysis of the oxidative specificity ofA.suboxydanstowards methyl glycopyranosides is presented.

ISSN:0008-4042    

DOI:10.1139/v78-284

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride gives both diastereomers of the adduct 1-tert-butyl-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienyl acetate and one diastereomer of 1-tert-buty]-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienol, in 91% yield, together with 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene. Solvolysis of the dienyl acetate in acidified aqueous acetone and acidified methanol affords the diastereomers of the dienols and the dienyl methyl ethers, respectively. The dienyl methyl ethers are also formed from the dienyl acetate in neutral methanol and again on reaction with methanolic sodium methoxide. The dienols isomerize (epimerize) in acidified aqueous acetone. Reaction of the dienyl methyl ethers in aqueous methanol, or prolonged reaction in methanol, results in the formation of methyl-1,2,3-trimethylphenyl ether. Similar cleavage of thetert-butyl group is the main reaction on solvolysis of the dienyl acetate in aqueous acetic acid. Under more acidic conditions the dienyl acetate gives 5-tert-butyl-2,3-dimethylbenzyl nitrite and lesser amounts of 5-tert-butyl-2,3-dimethylphenylnitromethane and 5-tert-butyl-2,3-dimethylbenzyl acetate. In trifluoromethanesulfonic and fluorosulfonic acids 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene is the major product.

ISSN:0008-4042    

DOI:10.1139/v78-285

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

When alumina was doped with molybdenum oxide, the concentration of the electron accepting sites increased linearly up to 18 wt% MoO3, and then decreased. The colour of the Mo–alumina changed from whitish yellow to grayish black when degassed at 320 °C for 2 h. This depended on the concentration of Mo. A strong signal for Mo5+was observed. Oxygen species were formed when the degassed sample was treated with oxygen or air. A reversible behaviour of oxygen on these species was observed. A possible mechanism has been discussed for the formation of O2−species and the reversible behaviour of oxygen. The concentration of electron accepting centers has been correlated with the activity for the hydrodenitrogenation of heavy oils over MoO3–alumina catalysts.

ISSN:0008-4042    

DOI:10.1139/v78-286

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The crystal structure of di-(μ-hydroxo)tetrakis(triethylphosphine)diplatinum(II)fluoroborate has been determined and refined to anRvalue of 0.032. The space group isP21/cand the cell dimensions area = 1.604(1),b = 1.847(1),c = 1.336(1) nm, β = 101.6 °, with 4 molecules per unit cell. The dimeric cation consists of two square planar Pt(II) centres bridged by a pair of hydroxo ligands. The angle between the mean plane normals is 36.4°. One of the BF4−groups, situated close to the dihydroxo bridge on the more open side, and having lower thermal parameters than the second fluoroborate anion, is hydrogen bonded to the oxygen atoms. The hydrogen atoms were not located. The interatomic distances (pm) are Pt—P = 223.5 (mean), Pt—O = 213.3 (mean), Pt(1)—Pt(2) = 312.1(1), O(1)—O(2) = 272(2), O(1)—F(1) = 288(2), O(2)—F(2) = 282(3). The mean bond angles (deg) are O—Pt—O = 79.4, P—Pt—P = 97.7, P—Pt—O = 91.5, and Pt—O—Pt = 94. One of the triethylphosphine groups is disordered or in thermal motion and was refined by constrained least squares using two superimposed partial structures. The results are discussed in relation to other known hydroxo bridged platinum species relevant to the field of platinum containing, cancer chemotherapeutic drugs.

ISSN:0008-4042    

DOI:10.1139/v78-287

出版商:NRC Research Press    

年代:1978

数据来源: NRC