摘要:

The reaction of ethyl 2,4,6-trinitrophenyl ether with aniline in dimethyl sulfoxide containing Dabco occurs in two stages. The first gives5, the &sgr; -adduct intermediate on the substitution pathway, which has been identified spectroscopically. The second yields 2,4,6-trinitrodiphenylamine, the substitution product. Kinetic studies show that proton transfer is rate limiting both in the formation of the intermediate and in its subsequent acid-catalysed decomposition. Phenoxide is a considerably better leaving group than ethoxide and the substitution reactions of phenyl 2,4,6-trinitrophenyl ethers and phenyl 2,4-dinitronaphthyl ether with aniline in DMSO occur without the accumulation of intermediates. The kinetics indicate both uncatalysed and base-catalysed pathways. The kinetic and equilibrium data for reaction of the ethyl and phenyl ethers are compared with data for &sgr; -adduct formation from 1,3,5-trinitrobenzene and aniline.Key words: nucleophilic substitution, proton transfer, base catalysis, &sgr; -adducts

ISSN:0008-4042    

DOI:10.1139/v97-225

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

1,2,4-Triazole stabilized allene anions are intermediates for the synthesis of 4-alkyl-2(5H)-thiophenones and 8-phenylimino-1,2,4-triazolo[5,1-c]-1,4-thiazines. Structures are confirmed by X-ray crystallography.Key words: allene anion, 4-alkyl-2(5H)-thiophenones, 8-phenylimino-1,2,4-triazolo[5,1-c]-1,4-thiazines, X-ray crystallography.

ISSN:0008-4042    

DOI:10.1139/v98-001

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The relationship between the rate constants that describe the halide ion catalysis of the racemization (kr) of optically alkyl halides and the related isotopic halide exchange reaction (ke) is shown to be valid in two distinct cases. The first is when the racemization and exchange mechanisms follow the classical and conventional SN2 path characterized by a symmetrical trigonal (sp2) transition state. The second envisages the trigonal species characteristic of the SN2 reaction as an intermediate instead of a transition state. The latter mechanism is also shown to be characterized by the relationshipkr= 2ke, and hence this diagnostic test is seen to be a necessary but not a sufficient condition for invoking the SN2 mechanism.Key words: racemization, isotopic exchange, kinetics, bimolecular substitution, inversion.

ISSN:0008-4042    

DOI:10.1139/v97-224

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Reaction rate constants obtained in moderately concentrated sulfuric acid for the hydrolysis of simple lactams of ring sizes five, six, seven, and eight as a function of acidity and temperature have been analyzed using the excess acidity kinetic method. The basicity constants for these substrates have been recalculated; the13C NMR spectra used to obtain these values are very sensitive to medium effects. It was found that the basicities of the lactams at 0.003-0.1 M lactam concentration were over half a pKunit more basic than they were at 0.5 M lactam, presumably because of the medium effect. Apart from this, the rate constant results obtained at different times by different groups using different techniques for monitoring the kinetics are in adequate agreement. The excess acidity analysis showed that the kinetics could be fitted according to the "three-water-molecule followed by one-water-molecule" mechanistic scenario previously found, or could just as well be fitted by a "one-water-molecule followed by unknown mechanism" scenario, with the mechanistic change taking place at 50 wt.% sulfuric acid for all the substrates. Other evidence makes the latter seem the more likely possibility of the two, and activation parameters based upon the "one-water-molecule" process were determined. Sufficient data points to enable the unknown mechanism to be established were not present; possible mechanisms applicable in media more concentrated than 50 wt.% sulfuric acid are discussed. Previously obtained values of the parameterr, the number of water molecules involved with the substrate in A2 processes, are now questionable.Key words: amides, lactams, excess acidity, hydrolysis, mechanism.

ISSN:0008-4042    

DOI:10.1139/v98-012

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The acidity constant, pQaE= 8.49, for the stable thioenol, triphenylethenethiol, was determined by spectrophotometric titration, and that, pQaE= 11.37, for its unstable oxygen analog, triphenylethenol, was determined by analysis of its ketonization rate using enol generated flash photolytically from triphenylvinyl bromide. (These acidity constants areconcentrationquotients applicable at 0.10 M ionic strength in 50 vol.% aqueous methanol.) This appears to be the first determination of the acid strength of a simple thioenol. Triphenylethenethiol was unreactive in dilute acid or base, but in concentrated perchloric acid solutions it was slowly transformed into diphenylacetophenone and 2,3-diphenylbenzo[b]thiophene; the mechanisms of these reactions are believed to involve rapid equilibrium protonation of the enol on the beta -carbon followed by rate-determining capture of the cation so formed, either externally by solvent or internally by one of the beta -phenyl groups of the ion.Key words: enol ketonization, thioenol, flash photolysis, vinyl halide.

ISSN:0008-4042    

DOI:10.1139/v98-027

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides (1, Pi-DNBT (x= 3);2, DNP-DNBT (x= 2);3, NP-DNBT (x= 1)) are electron-deficient nitro-substituted heteroaromatic substrates that possess two sites for nucleophilic attachment: C-7 and C-1'. Generally, attack at the super-electrophilic C-7 site yields spectroscopically observable anionic sigma -bonded adducts, whereas attack at C-1' leads to displacement products in an overall process of nucleophilic aromatic substitution (SNAr). To gain an understanding of the factors affecting C-1' versus C-7 attack by potentially ambident aryloxide (C- and O-)nucleophiles, we have monitored the reactions of1-3with 2,6-di-tert-butylphenoxide (2,6-ArO-) and 3,5-di-tert-butylphenoxide (3,5-ArO-) using 400 MHz1H NMR spectroscopy (deuterated dimethyl sulfoxide solvent at ambient temperature). The results indicate that 2,6-ArO-acts only as a C-nucleophile with O-attack precluded, presumably by the sterically demandingtert-butyl groups flanking the O-nucleophilic centre. Although 2,6-ArO-reacts preferentially at C-7 of1-3, the biphenyl derivative that arises from C-1' attack is also observed with1, the first time that C-nucleophilic attack has been seen at this electrophilic site. In contrast, 3,5-ArO-acts only as an O-nucleophile, also as a consequence of the steric hindrance to the C-4 position; this aryloxide reacts entirely at C-1' of Pi-DNBT but also exclusively at C-7 of3. However, with DNP-DNBT,2, both the C-7 O-adduct and C-1' displacement products are noted; attack at C-1' is dominant. The selectivity (C-7 versus C-1') found in these reactions is discussed with emphasis given to stereoelectronic factors that may stabilize the putative C-1' O-adducts.Key words: aryloxides, super-electrophiles, Meisenheimer complexes, 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides.

ISSN:0008-4042    

DOI:10.1139/v98-028

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Distorted amides 3,4-dihydro-2-oxo-1,4-ethanoquinoline (1a), 3,4-dihydro-2-oxo-1,4-propanoquinoline (1b), 3,3,4,5-tetrahydro-2-oxo-1,5-ethanobenzazepine (1c), and 3,3,4,5-tetrahydro-2-oxo-1,5-propanobenzazepine (1d) and the model compounds 2,N-dimethyl-acetanilide (2a), 2,N,N-trimethylaniline (3), and benzoquinuclidine (4) have been studied calculationally and with He(I) ultraviolet photoelectron spectroscopy. We find good agreement between experimentally obtained ionization energies for1b,1c,1d,2a,3, and4and values calculated with HAM/3 using the equilibrium geometries obtained at the HF/6-31G** level of theory. An excellent correlation between experimental ionization energies and orbital energies from Becke3LYP/6-31+G* calculations led to the characterization of the highest occupied molecular orbitals for these compounds and for1a,whose photoelectron spectrum could not be obtained due to its reactivity in the solid state.Key words: distorted amides, He(I) photoelectron spectroscopy, Becke3LYP, molecular orbitals.

ISSN:0008-4042    

DOI:10.1139/v97-231

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The bimolecular reactions of azide, 2-iodosobenzoate, and acetohydroxamate ions and methoxyamine nucleophiles with substituted phenyl acetates possess Yukawa-Tsuno type correlations with substantial resonance interaction. The rate constants for hydroperoxide ion and the oxyanion ofN,N-diethylhydroxylamine obey simple Hammett equations. The reactivities of azide, acetohydroxamate, hydroperoxide, and 2-iodosobenzoate ion nucleophiles exhibit modest alpha -effects when the reactivity in substitution at 4-nitrophenyl acetate is compared with that of phenoxide ions of similar pKavalues. TheN,N-diethylhydroxylamine oxyanion is less reactive than its phenoxide ion analogue due to steric requirements, and the reactivities of the anionic nucleophiles exhibit changes in effective charge on the leaving oxygen similar to those for regular nucleophiles of similar pKa. Methoxyamine possesses only a small enhancement compared with the reactivity of a normal primary amine of similar pKa.Key words: alpha -effect, nucleophile, Yukawa-Tsuno, Leffler, Hammett, phenyl ester, effective charge, Brønsted.

ISSN:0008-4042    

DOI:10.1139/v98-009

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Syntheses and negative solvatochromism of two new lipophilic pentaphenyl pyridiniumN-phenolate betaine dyes, substituted with seventert-butyl groups (9) or with threetert-butyl and two 1-adamantyl groups (13) in the peripheral phenyl rings, are described in order to get zwitterionic dyes that are more soluble in nonpolar solvents such as the standard betaine dye,1, which has been used for the construction of an empirical scale of solvent polarity, called theET(30) scale.Key words: betaine dyes,ET(30) values, lipophilic dyes, pyridiniumN-phenolate betaine dyes, solvatochromism, solvent polarity.

ISSN:0008-4042    

DOI:10.1139/v98-019

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A series of 5-(alkyloxy)thianthrenium perchlorates has been made in which the alkyl group is primary (1a-1p) and secondary (2a-2g). Preparations were carried out by reaction of the corresponding alkanol with thianthrene cation radical perchlorate in CH2Cl2solution followed by precipitation of the perchlorate salt with dry ether.1H NMR spectroscopy reveals that the presence of a stereogenic center in the alkyl group causes inequivalence in the ordinarily paired protons (e.g., H-4, H-6) of the thianthrenium ring. Reaction of iodide and bromide ion with primary alkyl-group compounds (e.g., methyl, ethyl, propyl, butyl) gave the alkyl halide in very good yield and by a second-order kinetic displacement. The second product was thianthrene 5-oxide (ThO). Rate constants for some of these reactions are reported. Reaction of secondary alkyl group compounds (e.g., 2-propyl, 2-pentyl, 2-hexyl, and 3-hexyl) with iodide ion gave good yields of alkyl iodide but also increasing evidence for a side reaction at the sulfonium sulfur, leading to I2, thianthrene, and secondary alkanol. Decomposition of some compounds at 100°C in solution (acetonitrile or 1,2-dichloroethane) was studied and gave alkene(s) and ThO.Key words:thianthrene cation radical, 5-(alkyloxy)thianthrenium perchlorates.

ISSN:0008-4042    

DOI:10.1139/v98-010

出版商:NRC Research Press    

年代:1998

数据来源: NRC