摘要:

The surfaces forcis–transisomerization and racemization of the cyclopropane radical cation (1+) are determined usingabinitiocalculations. It is found that polarization functions and electron correlation have large effects on the relative energies of1+. Orbital symmetry arguments predict that conrotatory closure of the 0,0 conformer of1+should be preferred. These predictions are supported by the calculations; however, even the conrotatory closure has a significant activation barrier. Conformational changes that accompany single methylene rotation are also discussed. The implication of these results to ion cyclotron resonance and mass spectral experiments is that isomerization of1+to the 0,0 conformer can occur at energies far below the barrier required to isomerize1+to the propylene radical cation. However, the 0,0 conformer of1+and the propylene radical cation should display similar reactivities (e.g. deprotonation). The results also indicate that, contrary to reported esr evidence,1+should not exist preferentially in the 90,0 conformation.

ISSN:0008-4042    

DOI:10.1139/v85-543

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A number of lumazines and 5-deazalumazines containing a methyl group at C-7 have been prepared, their pKBH+values determined, and measurements made of the rates at which the hydrogen atoms of their 7-methyl groups undergo isotopic exchange in aqueous sulfuric acid. The presence of an alkyl group at N-8 in the protonated forms of these compounds activates the neighbouring methyl group at C-7; the effect is considerably larger than that previously observed for a methyl group at C-6, which is the other neighbouring position. The comparison of methyl and hydrogen at N-8 can be made only for the acid-catalyzed reaction because the structures of the neutral compounds, which take part in the base-catalyzed reaction, are not analogous.

ISSN:0008-4042    

DOI:10.1139/v85-544

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The differential equations which describe the kinetics of the general reactionare cast in a nondimensional form and analysed. The problem reduces to two first-order nonlinear ordinary differential equations containing three nondimensional constants together with two initial conditions. Composition–time curves are deduced for the general case. For the case when, where [A]0is the initial concentration of A, simple analytical solutions are obtained. Numerical integrations of the full equations are reported and the analytical solutions are found to represent accurate solutions to the nonlinear problem for sufficiently small values ofk2.

ISSN:0008-4042    

DOI:10.1139/v85-545

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The crystal structure of a chiralm-cyclophane, the α-isomer of (S)-α-methoxy-α-(trifluoromethyl)phenylacetate ester of 13-(methoxycarbonyl)-14-hydroxy-17-methyl-[11]-m-cyclophane (C30H37O5F3, FW = 534.62) has been solved by direct methods and refined by a least-squares procedure to a finalR = 0.048 for 2756 independent reflections. The crystals belong to the orthorhombic system,a = 10.8077(13),b = 13.676(3),c = 19.060(4) Å,V = 2817.2 Å3,Z = 4, and the space group isP212121. The absolute configuration of the chiral plane, using theS-configuration of the α-methoxy-α-(trifluoromethyl)phenylacetate ester as reference, is found to beS, in agreement with the X-ray result. The 14-membered ring has the slightly distorted rectangular conformation that has been described by Dale as the rectangular diamond-lattice conformation [3434]. The distortions, also observed in similar 14-membered rings, have been successfully approximated by molecular mechanics calculations.

ISSN:0008-4042    

DOI:10.1139/v85-546

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The quantitative conversion of fluorosulfates into trifluoromethyl sulfates is systematically investigated. The reaction proceeds initially according to the general equationwhere E is a coordinatively saturated metal or an organometallic moiety. However, the key to a quantitative substitution is the observed degradation of the SO3F group by excess HSO3CF3and the noted observation of various volatile by-products that do not appear to interfere in the isolation of analytically pure trifluoromethyl sulfates. The fluorosulfates selected are representatives of the most common bond and coordination types—ionic or covalent with coordination through one, two, or three oxygens of the SO3F groups. The selected substrates display a fairly wide range of solubilities in HSO3F. All conversion attempts are successful except for one, that of polymeric Hg(SO3F)2, and a number of new SO3CF3derivatives of tin, platinum, germanium, and palladium are described. The solvolysis of tin(IV) acetate in HSO3CF3is reinvestigated and the syntheses of two other trifluoromethyl sulfuric acid derivatives, CsSO3CF3•HSO3CF3and CH3CO2H•HSO3CF3, are described.

ISSN:0008-4042    

DOI:10.1139/v85-547

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Oxidation of 1,3-oxathiolan-5-ones (1) gives acceptable yields of sulfoxides only when C4 is unsubstituted. Sulfoxides derived from 1,3-thiazolidine-4-ones (8) are easily prepared. Acid-catalyzed rearrangement in the presence of 1-alkenes or benzene leads to alkylation (arylation) at C5. Alkylation of8cmay be generally more effective than that of1. An aldol condensation of8cshows little stereoselectivity.

ISSN:0008-4042    

DOI:10.1139/v85-548

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The initial oxidation stages of lactic acid by acid permanganate were investigated. The rate of the induction period was slow and then gradually increased. The kinetics of oxidation were second order, first order with respect to both lactic acid and Mn(VII). The reaction was acid catalyzed. Addition of Mn(II) ions largely increased the rate of the initial stages and decreased the rate of the following stages. The oxidation rate was decreased by the addition of F−orions. The Arrhenius equation was valid for the reaction between 16.5 and 34 °C. Activation parameters were evaluated and a mechanism consistent with the results obtained was proposed.

ISSN:0008-4042    

DOI:10.1139/v85-549

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The crystal structure of thomsenolite, NaCaAlF6•H2O, has been redetermined to establish the hydrogen-bonding scheme in this mineral. Both hydrogen atoms participate in branchedbonds. The hydrogen bonds link the AlF6, octahedra to form infinite chains ||b, which in turn are cross-linked to form infinite double sheets {[AlF6] + Ca}—(H2O)—{[AlF6] + Ca}||(001). The Na atoms are located exclusively in layers ||(001) which separate the double sheets. A detailed comparison of thomsenolite with its dimorph, pachnolite, shows that the structure of pachnolite is obtained in essence by interchanging the positions of one half of the Na atoms and one half of the water molecules in thomsenolite. The two-dimensional, layerlike hydrogen-bonding network in thomsenolite is thereby changed to one of a three-dimensional character in pachnolite. Other features of the two structures, including the Al—F anddistances, are compared and discussed in some detail.

ISSN:0008-4042    

DOI:10.1139/v85-550

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The ir spectra of the isotopic probe ion NH3D+have been used to obtain information about the symmetry, orientation, and hydrogen-bonding involvement of the ammonium ion, between 10 K and room temperature, in NH4F, NH4HF2, (NH4)2[Cr(H2O)6]F5, NH4PF6, (NH4)3SiF7, the elpasolites (NH4)2BFeF6(B = Na, K) and CS2NH4MF6(M = Fe, Al), and the cryolites (NH4)3MF6(M = Al, Cr, Fe). Several of these fluorides exhibit low-temperature transitions, some of which are evident in the probe-ion spectra. It is shown that relating the isotopically isolated ND stretching and bending frequencies to thedistances and to the coordination numbers of the ammonium ion reveals important trends in the dependence of the behaviour of the ion on its immediate environment in the crystal. A detailed discussion is presented of the effect of ionic size and the geometric tolerance factorton the transition temperatures of cubic cryolite, perovskite, and elpasolite halides, as well as on the anisotropy of the principal thermal amplitudes of the halogen atom in such compounds. The relation betweenTtrand the frequency of the ND stretching absorption of NH3D+in the ammonium representatives of these classes of halides is also explored.

ISSN:0008-4042    

DOI:10.1139/v85-551

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The excess molar volumes,, of 2-hexanone (MBK) withn-hexane,n-heptane,n-octane,n-nonane,n-decane,n-undecane,n-dodecane, andn-tridecane have been obtained at 298.15 K from densities measured with a vibrating tube densimeter. Theare positive over the entire composition range in all mixtures, with the exception of the MBK + n-hexane system, where an inversion of the sign ofis observed. In other systems,increases with increasing size of the alkyl group inn-alkane.

ISSN:0008-4042    

DOI:10.1139/v85-552

出版商:NRC Research Press    

年代:1985

数据来源: NRC