摘要:

The stereofacially differentiated enone aldehyde11was chosen to study the effects of steric and electronic influence on the Diels–Alder reaction. Under Lewis acid catalysis,11adds to dienes at low temperatures at a reasonable rate. Yields of desired chiral adducts are good to high with zinc chloride and boron trifluoride etherate catalysis. In all cases only products of addition to theReface of general type27were observed. The regiochemistry of the adducts is exclusively that predicted by theorthoandpararules. The stereochemistry shows a very high selectivity in favour of aldehyde-endotransition state products. Unusual byproducts were also obtained in some examples and mechanisms of these unexpected reactions are discussed.

ISSN:0008-4042    

DOI:10.1139/v94-240

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Condensation of pyrrole with a benzaldehyde and 4-pyridinecarboxaldehyde mixture yields the six possiblemeso-substituted phenyl or pyridyl porphyrins. Nitration of four of these has yielded 13 other porphyrins containing one to four 4-nitrophenyl moieties, and SnCl2reduction of eight of these nitrophenylporphyrins gives the corresponding 4-aminophenyl(phenyl)- or 4-aminophenyl(phenyl)(4-pyridyl)-porphyrins. Twelve of the porphyrins are new, but all 27 are fully characterized by1H NMR; resonances for every proton within each of the phenyl, pyridyl, and pyrrole rings are assigned. Trends in UV–VIS data are discussed, while IR and mass spectral data are noted for selected porphyrins.

ISSN:0008-4042    

DOI:10.1139/v94-241

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A study of the rates of the cyclizations1 → 3and2 → 4as a function of medium acidity and temperature in aqueous sulfuric acid has been performed. The latter reaction is five times faster at all acidities. An excess acidity kinetic analysis reveals the probable involvement of a water molecule in the reaction in both cases. Mechanistic possibilities suggested by the observations are discussed; it is proposed that the water molecule acts as a base catalyst during the rate-determining ring closure.

ISSN:0008-4042    

DOI:10.1139/v94-242

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

We have measured (du Nouy ring and maximum bubble pressure methods) suspension–air surface tensions of aqueous suspensions of montmorillonite and have observed that these surface tensions are larger than those of pure water at the same temperatures. Further measurements have shown that dispersed montmorillonite also increases the suspension–toluene interfacial tension compared with that of pure water–toluene. Similar measurements on aqueous suspensions of kaolinite have yielded suspension–air interfacial tensions with uncertainties as large as the observed (small) effect, and also shown that the suspension–toluene interfacial tension is decreased (opposite to the effect of montmorillonite) by amounts larger than the experimental uncertainties. Measurements of maximum bubble pressures at different flow rates have provided information about the effect of surface age on observed surface tensions.

ISSN:0008-4042    

DOI:10.1139/v94-243

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Excess volumesVE, excess viscosities ηE, and excess free energies of activation of flowG*Eof binary mixtures of 2-chloro-2-methylpropane with isomeric butanols have been calculated from experimental measurements of density and viscosity at 298.15 K. The results are correlated by means of a Redlich–Kister type equation and explained in terms of molecular interactions.

ISSN:0008-4042    

DOI:10.1139/v94-244

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The configurational isomers of the title compounds consist of four fused five-membered rings. They contain tightly coupled1H NMR spin systems, which provide excellent models for establishing the relationships between coupling constants and conformation. Complete chemical shift assignments and spin–spin coupling constants are reported for the title compounds by using high-field (500 MHz)1H NMR techniques (e.g., 2D homonuclear and heteronuclear experiments, difference NOE enhancements, and computational spin simulations). In addition to the more familiar two- and three-bond couplings, the spectra of1and2also contain a number of long-range (four- and five- bond) couplings, which provide a stringent test of Barfield's theoretical treatment of four-bond couplings.

ISSN:0008-4042    

DOI:10.1139/v94-245

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Second-order rate constants for the demethylation of three phosphate esters by thiophenoxide salts, PhS−M+(M+ = Me4N+, K+, Na+, Li+) in methanol-d4at 25 °C have been measured. In contrast to the demethylation by iodide salts, metallic counterions do not exhibit any catalytic effects on the demethylation rate. The absence of the catalysis indicates that the salts react exclusively as ion pairs, in which an alkali metal ion is not available for the interactions with the phosphoryl group in the transition state.

ISSN:0008-4042    

DOI:10.1139/v94-246

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The density and shear viscosity of mixtures oftert-butyl alcohol (BuOH) andtert-butylamine (TBA) with water have been determined for various temperatures (288 to 318 K for H2O + BuOH and 288 to 308 K for H2O + TBA) over the whole composition range. Excess molar volumes and apparent molar volumes of the components of each system were calculated from the density data. In both systems the apparent molar volume of the organic component passes through a minimum in the water-rich region. Both systems exhibit large negative excess molar volumes which are essentially independent of temperature at all compositions. The two systems show pronounced maxima in their shear viscosity isotherms.

ISSN:0008-4042    

DOI:10.1139/v94-247

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The13C NMR spectra of [M(NH3)5(styrene)]2+(M = Ru, Os) demonstrate the substituent dependency of the interaction between the vinyl group and the metal moiety which suggests the modes of bonding. This phenomenon is also observed from the voltammetric analytical results which confirm the substituent dependency of the oxidation potential.

ISSN:0008-4042    

DOI:10.1139/v94-248

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In order to provide experimental evidence on the stereoelectronic requirements for intramolecular hydrogen atom abstraction by carbonyl oxygen,N-(tert-butyl)succinimide,1, was investigated by the crystal structure – reactivity correlation method. In this method, the success or failure of a given reaction in the crystalline state is correlated with the geometric parameters associated with the process as determined by X-ray crystallography. In the case ofN-(tert-butyl)succinimide, the crystal and molecular structure shows that the molecule adopts a conformation in which there are very close contacts (d = 2.17–2.24 Å) between the carbonyl oxygen atoms and certain γ-hydrogen atoms on thetert-butyl group. In accord with these close contacts, ultraviolet irradiation ofN-(tert-butyl)succinimide in the crystalline state leads to transfer of one of the γ-hydrogen atoms from carbon to oxygen. This produces a 1,4-biradical which closes to form a cyclobutanol, and the cyclobutanol undergoes ring opening to afford the final stable product, tetrahydro-1H-azepine-2,5-dione,2. The crystal and molecular structure of photoproduct2is also reported. In contrast to many solid state transformations, there was no discernable melting of the crystals during reaction, and complete conversions of1into2could be achieved. The isolated chemical yield of photoproduct2from the solid state reaction (79%) is in fact considerably higher than that reported by Kanaoka and Hatanaka for the corresponding solution phase process (49%). This permitted the solid state reaction to be followed to 100% conversion by X-ray powder diffractometry, which showed that the process is a single crystal-to-polycrystalline transformation involving a regular and progressive conversion of1into2with no obvious diffraction peaks that might be attributable to the intermediate cyclobutanol.

ISSN:0008-4042    

DOI:10.1139/v94-249

出版商:NRC Research Press    

年代:1994

数据来源: NRC