摘要:

Infrared spectra of ethyl α-aminoacetates show three bands in the carbonyl region. Solvent effects show that this is not due to Fermi resonance. These spectra can be interpreted using a model that considers the interactions between the nitrogen lone pair and the carbonyl group. The existence of an equilibrium between the conformers caused by the different orientations of the nitrogen lone pair with respect to the carbonyl group can be forecast. This model enables the interpretation of the carbonyl absorptions of the α-substituted (methoxy and ethoxy) ethyl acetates.

ISSN:0008-4042    

DOI:10.1139/v85-388

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The kinetics of oxidation of serine and threonine by periodate have been investigated in acid medium at 10 °C. The reaction rate is first order in both periodate and amino acid, and the overall reaction follows second-order kinetics. The rates decrease with increase in [H+]. A catalytic effect of the buffers was not observed in the oxidation process. An analysis of the dependence of the rate on [H+] reveals that the reactive species under the experimental conditions are periodate monoanion and dianion and the dipolar form of the amino acid. The mechanism proposed and the derived rate law are consistent with the observed kinetics. The rate constants predicted using the derived rate law are in agreement with the observed rate constants, thus justifying this rate law and hence the proposed mechanistic scheme.

ISSN:0008-4042    

DOI:10.1139/v85-389

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Syntheses of numerous 2-aryl nitroethylenes (nitrostyrenes) have been optimized. The nitrostyrenes have been reacted with cyclopentadiene in Diels–Alder cycloadditions and the 3-aryl 2-nitronorbornenes obtained have been reduced into 3-aryl 2-aminonorbornenes. These compounds are potentially dopaminergic molecules. The stereochemistry of the adducts obtained in the Diels–Alder reaction has been determined by1H nmr. The stereochemistry and the relative reactivity of the nitrostyrenes versus cyclopentadiene have been confirmed by theoretical calculations based on the CNDO/II method.

ISSN:0008-4042    

DOI:10.1139/v85-390

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The regiospecific 1,3-dipolar cycloaddition reaction of 1,2-dihydropyridines2with organic azides3affords 2,7-diazabicyclo[4.1.0]hept-4-enes4. Treatment of4awith neutral aluminum oxide opened the aziridine ring to afford the 1,2,5,6-tetrahydropyridylidene-2-cyanamide5. Catalytic hydrogenation of4and5using palladium-on-charcoal and hydrogen yielded the 1-methyl-2-piperidylidenes6. Oxidation of 1-methyl-1,2,5,6-tetrahydropyridylidene-2-cyanamide (5) with alkaline hydrogen peroxide yielded the oxirane7arising from epoxidation of the 3,4-olefenic bond, whereas oxidation of the bicyclic aziridine4awithm-chloroperbenzoic acid resulted in epoxidation of the 4,5-olefenic bond and opening of the aziridine ring to give the oxirane 3-methyl-3-aza-7-oxabicyclo[4.1.0]heptylidene-4-cyanamide (10). Base-catalyzed abstraction of the C-3 proton of 1-methyl-2-piperidylidenes6yielded the 3-lithio analogs which, after bromination, were converted to the target compounds18upon condensation with 4-[(2-aminoethyl)thiomethyl]-5-methylimidazole.

ISSN:0008-4042    

DOI:10.1139/v85-391

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Spectroelectrochemistry at an optically transparent electrode, in conjunction with controlled potential coulometry, has been used to study the Tc(IV)/Tc(III) redox couple in aqueous bicarbonate solutions. The complexation provided by bicarbonate/carbonate ions was found to stabilize both Tc(IV) and Tc(III). The uv–visible absorption spectra for technetium(III) and technetium(IV) carbonate complexes are described. The redox potential for the Tc(IV)/Tc(III) couple, as well as the number of electrons, the number of carbonate groups, and the number of hydroxyl groups exchanged during the redox process in bicarbonate media are reported.

ISSN:0008-4042    

DOI:10.1139/v85-392

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

It is shown that there will be strong orienting effects in the collision of two radicals which will invalidate attempts to calculate disproportionation–recombination ratios by simple geometric arguments.

ISSN:0008-4042    

DOI:10.1139/v85-393

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effects of substituents in themetaandparapositions of the benzyl radical on the α-hydrogen hyperfine coupling constants (hfc's) are discussed. The electron spin resonance (esr) spectra of thepara-methyl, ethyl, isopropyl, andtert-butyl substituted benzyl and cumyl radicals are analysed. Hyperconjugation involving the C—C bond is 40–60% as effective as C—H hyperconjugation for delocalizing spin density. This conclusion is supported by INDO molecular orbital calculations. Similar analysis of the13Cmr spectra of thepara-alkyl substituted cumyl carbocations provides evidence that C—C hyperconjugation is 75–90% as effective as C—H hyperconjugation for delocalizing charge density.

ISSN:0008-4042    

DOI:10.1139/v85-394

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Starting from 2,3-dihydrofuranic compounds, we prepare the corresponding α-bromohydrines and α-bromo-butyrolactones. A solvolytic method of equilibration of these bromolactones in DMF is described. All the stereoisomers are separated and studied. With a Cβ substituant, the elimination promoted by a weak base (LiBr) gives the Δ2butenolide in good yield, whatever the starting isomer configuration may be. An application is given with the stereoselective synthesis of a trisubstitued ethylenic γ-diol with a Z configuration.

ISSN:0008-4042    

DOI:10.1139/v85-395

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Nitration of 1,2-dimethyl-4-nitrobenzene in a mixture of acetic anhydride and trifluoroacetic anhydride gives the diastereoisomers of 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-dienyl acetate (50%), in addition to the 1,2-dimethyldinitrobenzenes. In moderate and more strongly acid conditions the adduct gives 4-nitro-, 3,4-dinitro-, and 3,5-dinitro-o-xylene. In neutral and weakly acid solutions 4-nitro- and 3,5-dinitro-o-xylene are formed by a radical and a sigmatropic pathway. The adduct reacts facilely with nucleophiles by allylic substitution to give a 5,6-dimethyl-6-nitrocyclohexa-2,4-dienyl derivative which, in many instances, undergoes a second allylic substitution to a new 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-dienyl derivative. Depending on the nature of the introduced substituent, these 2,4- and 2,5-dienyl products may eliminate nitrous acid, under the reaction conditions, to give the corresponding aromatic compound. The dienyl acetates undergo acid-catalysed transesterification to the corresponding dienols.

ISSN:0008-4042    

DOI:10.1139/v85-396

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The photocycloaddition of allene to the steroidal enone1a, normally occurring from the (less hindered) α side, has been directed in part to the (more hindered) β side by adsorption on the surface of silica gel. For a series of cyclic enone–allene photocycloadditions it is shown that the normally favored formation of the β,γ-regioisomeric adduct in homogeneous systems can be shifted to favor the γ,δ adduct on a silica gel surface.

ISSN:0008-4042    

DOI:10.1139/v85-397

出版商:NRC Research Press    

年代:1985

数据来源: NRC