摘要:

Rate constants are reported for hexachloroiridate(IV) oxidation of iodide in methanol–, ethanol–,t-butyl alcohol–, ethylene glycol–, glycerol–, acetone–, acetonitrile–, and dimethyl sulphoxide – water solvent mixtures, and for the hexachloroiridate(IV) oxidation of catechol in methanol–water mixtures. With the aid of ancillary solubility data and measurements, solvent effects on reactivity have been analysed into initial state and transition state components. In the latter, there are probably both electron transfer and diffusion contributions since it is not possible to identify uniquely the separate kinetic steps associated with the activation process. In these redox systems, however, transition state solvation changes dominate. This conclusion is compared with initial state – transition state effects in the reaction of catechol with hexahydroxoantimonic acid, in the bromate oxidation of bromide, the peroxodisulphate oxidation of iodide, and with patterns established earlier for substitution at inorganic centres. In view of some disagreements and uncertainties in the literature concerning the number of molecules of water of crystallisation in potassium hexachloroiridate(III) and hexachloroiridate(IV), this matter, of considerable importance to hexachloroiridate transfer parameter estimation, is briefly reviewed.

ISSN:0008-4042    

DOI:10.1139/v83-239

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Usingabinitiovalence double zeta as a basis, a quantum-chemical approach was developed for the models HP=NH and PH=CH2. The geometric parameters were determined by a variable metrics minimization process.The 2pπ–3pπbond forces for P=N and P=C were estimated by evaluating the barriers obtained by a 90° rotation of one part of the molecule with respect to the other. The essential correlation effect was considered and a rigourous RHF formalism was used to determine the state at 90° of lower energy.Different electronic characteristics were found for both motives and according to these results, their reaction behaviour was interpreted: dimerization, addition of polar reactants, and protonation site for HP=NH.

ISSN:0008-4042    

DOI:10.1139/v83-240

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The formation of Mannich bases from the reaction of silyl enol ethers withN-methyl-N-mesitylmethyleniminium salt, generated by the electrochemical oxidation ofN,N-dimethylmesidine, was studied. Important factors influencing the reaction are: (a) the silyl enol ether must be nucleophilic enough to react with the iminium salt and, at the same time, must be more difficult to oxidize than the tertiary amine, (b) the product of the reaction must not be oxidized at the operating potential. Examples are presented in this paper illustrating the successes and limitations of this reaction.

ISSN:0008-4042    

DOI:10.1139/v83-241

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The resolution of 2-tetrahydrofuran-carboxylic acid and assignment of configuration to the enantiomers are reported. New syntheses of the enantiomers of 2-tetrahydrofurancarboxaldehyde are also described.

ISSN:0008-4042    

DOI:10.1139/v83-242

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The synthesis and properties, particularly1H,31P, and13C nmr, of new phosphate esters of 1,2-O-isopropylidene-α-D-ribo-and xylo-furanoses are described. For the cyclic phosphates the configuration at the asymmetric phosphorus atom is determined and for all derivatives the preferred conformation of the furanose and dioxaphosphorinane rings and the conformation around the phosphoester bonds are presented. The dependency of3JPOCCcoupling constants on factors other than dihedral angles is reported and discussed.

ISSN:0008-4042    

DOI:10.1139/v83-243

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

1,4-Dibenzyl-3-hydroxy-3-[1-(2-methoxyethyl)ethenyl]piperazine-2,5-dione (43), which incorporates several of the structural features of the antibiotic bieyclomycin, has been synthesized via a reaction sequence involving early construction of the piperazine-2,5-dione ring. In model studies 3-isopropylidenepiperazine-2,5-dione was di-N-benzylated and epoxidized to give 4,7-dibenzyl-2,2-dimethyl-1-oxa-4,7-diazaspiro[2.5]octane-5,8-dione (10). The opening of the epoxide ring of10by several reagents was investigated and it was found that treatment with magnesium isopropylcyclohexylamide (MICA) gives 1,4-dibenzyl-3-hydroxy-3-(1-methylethenyl)piperazine-2,5-dione (23). Treatment of ethyl 3-(2-methoxyethyl)-3-methyl-glycidate (28) withp-toluenesulfonic acid followed by hydrogenation and oxidation gives ethyl 5-methoxy-3-methyl-2-oxopentanoate, which on reaction with chloroacetamide and sulfuric acid followed by treatment of the resulting enamide with ammonia gives (Z)- and (E)-3-(4-methoxybut-2-ylidene)piperazine-2,5-dione. Di-N-benzylation of these followed by epoxidation gives (Z)- and (E)-4,7-dibenzyl-2-(2-methoxyethyl)-2-methyl-1-oxa-4,7-diazaspiro[2.5]octane-5,8-dione (41and42). Treatment of41with MICA converts it to compound43. Chromatography of43on silica converts it in part toN-benzyl-N-(2-benzylamino-2-oxoethyl)-3-(2-methoxyethyl)-2-oxo-3-butenamide, which on treatment with MICA regenerates43.

ISSN:0008-4042    

DOI:10.1139/v83-244

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

A 1% crosslinked divinylbenzene–styrene copolymer, incorporating vicinal diol groups or their isopropylidenc precursors, was used to form the monoacetals of the symmetrical diketones,p-diacetylbenzene, 1,2-cyclohexanedione, 1,3-cyclohexanedionc, 1,4-cyclohexanedione, and 2,5-hexanedione. The free ketone groups reacted with phenylmagnesium bromide to give, in high yield, after acid hydrolysis from the polymer, the expected products such as 3-phenyl-2-cyclohexen-1-one from 1,3-cyclohexanedione. The13C nmr spectra of some polymer-bound substrates and simple analogs are described.

ISSN:0008-4042    

DOI:10.1139/v83-245

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene are orthorhombic,a = 8.7283(6),b = 8.8369(5),c = 18.8798(8) Å,Z = 4, space groupP21ab. It is resolved toRF = 0.053 for 684 observed reflections. Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene hydrochloride are monoclinic,a = 14.6120(9),b = 5.2736(7),c = 20.708(1) Å, β = 102.287(5)°,Z = 4, space groupP21/c. The final residual is 0.054 for 1255 reflections. Crystals of 2-N-methylamino-4-N-methylimino-2-pentene hydrochloride are trigonal,a = 7.1666(7).c = 15.3299(8) Å,Z = 3, space groupP3121. The final residual is 0.044 for 343 observed reflections. The free base exists, in the solid, as the amino-imino form and not as a symmetrical structure. The N—H bond distances in the six-membered ring of the free base are equal as are the N—H bond distances in the infinite chains of the hydrochloride salts. The compounds are fluxional in solution.

ISSN:0008-4042    

DOI:10.1139/v83-246

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The partial molal volumes at infinite dilutionfor a number of halobenzenes are measured and related to their van der Waals volumes. Results indicate larger volume increments for halogen atoms in halobenzenes than those in alkyl halides. Possible explanations are forwarded. The effect of steric overcrowding inortho-substituted benzenes on thevalues are evaluated.

ISSN:0008-4042    

DOI:10.1139/v83-247

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Magnetic shielding constants, calculated for C-13 and N-15 nuclei in the finite perturbation method using INDO and London's approximations, are analyzed in terms of mono-, di-, and tricentric contributions, thus permitting an assessment of the relative importance of local vs. nonlocal contributions. For both C-13 and N-15, it appears that the changes in total shielding are almost entirely dictated by those of the local paramagnetic contribution, i.e.,.

ISSN:0008-4042    

DOI:10.1139/v83-248

出版商:NRC Research Press    

年代:1983

数据来源: NRC