摘要:

It has been claimed that trends in the thermodynamic properties of alkane isomers follow an ordering based on p2and p3, the number of paths of length two or three, respectively (M. Randic and C. L. Wilkins. J. Phys. Chem.83, 1525 (1979)). A possible explanation of the approximate ordering of the partial molal volumesof isomers in carbon tetrachloride at 25 °C comes from the ordering, based on p2and p3, of (a) the numberNof methyl groups, and (b) the mole fractionZgofgauchearrangements in the different isomers. However,NandZghave opposite effects on, and specific cases of isomeric heptanes and nonanes are noted in which a reversal in trends inmay be expected.

ISSN:0008-4042    

DOI:10.1139/v80-301

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Molar excess volumes,VEat 298.15 and 308.15 K, molar excess enthalpiesHEat 308.15 K, and total vapour pressure at 298.15 and 308.15 K. have been measured for binary mixtures of 1,2-dichloroethane with aromatic hydrocarbons. TheVEandHEdata for an equimolar mixture at 308.15 K only have been utilized to predictVE,HE, andTSEvalues (using Sanchez and Lacombe theory) for these mixtures as a function of temperature and composition. The agreement between the predicted and the corresponding experimental values is good so far asVEandHEdata are concerned but the same is not true of theTSEvalues.

ISSN:0008-4042    

DOI:10.1139/v80-302

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The pyrolysis of C6F5CH2Br has been studied by the toluene carrier technique over the temperature range 727–800 °C. Rate constants are based on analysis for residual parent compound by gas chromatography using an internal standard technique. In selected runs a material balance of 100 ± 2% was obtained for bromine based on C6F5CH2Br plus HBr. Within the limits of the experimental technique the process appears to be first order and homogeneous. In addition to HBr the other major products of the thermal decomposition are C6F5CH3, (C6F5CH2)2, C6F5CH2CH2C6H5, and (C6H5CH2)2. The Arrhenius equation obtained isThe logAvalue is very close to the value of 14.6 recommended by Benson and O'Neal for the decomposition of C6H5CH2Br. The activation energy, 225 ± 6 kJ mol−1, should be a reasonable estimate ofD[C6F5CH2—Br].

ISSN:0008-4042    

DOI:10.1139/v80-303

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The sonolysis of uracil (1) has been studied at 630 kHz in the presence of air, oxygen, nitrogen, and argon. The degradation products were identified by gc–ms analysis. Under aerated conditions the following products were found: uracil glycols (7), isobarbituric acid (8),N-formyl-N′-glyoxylurea (6), 5-hydroxyhydantoin (9), dialuric acid (10), alloxan monohydrate (12), parabanic acid (13), and oxaluric acid (14). In deaerated solutions6,13, and14were not observed but either 6-hydroxy-5,6-dihydrouracil(17) or its isomer (18) were detected in addition to7,8,9,10, and12. The observed products have been used to develop a possible mechanism for the sonolytic degradation and the results are similar to those obtained in radiolysis.The sonolytic degradation of 5-bromouracil (19) is also reported; the products observed were 5-bromobarbituric acid (20),12,13,14, and9and these can be rationalized by a similar mechanistic scheme.

ISSN:0008-4042    

DOI:10.1139/v80-304

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The nonselective spin–lattice relaxation rates (R1-values) have been determined for all of the ring protons of the eight isomers of 2,3,4-tri-O-acetyl-1,6-anhydro-(β-D-hexopyranose as 0.1 molar solutions in benzene-d6. The effects on the protonR1-values of changes in solvent, concentration, temperature, and proton impurities are documented and13CR1-values are given to show that the first two sets of variations are due to changes in motional correlation times of the molecules. The proton relaxation data can be fitted by regressional analyses to a single set of interproton relaxation contributions, the numerical values of which accord with a1C4conformation for the pyranose ring somewhat distorted by the 1,6-anhydro bridge.

ISSN:0008-4042    

DOI:10.1139/v80-305

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The non-selective proton spin–lattice relaxation rates of 3,5-di-O-acetyl-2,6-dibromo-2,6-dideoxy-D-mannono (1), or -glucono (2), 1,4-lactone, methyl-α,(β)-D-ribofuranoside (3), methyl-α,(β)-D-arabinofuranoside (4), methyl-α(β)-D-xylofuranoside (5), 3,5-di-O-acetyl-1-O-benzoyl-2,6-dibromo-2,6-dideoxy-α and β-D-mannofuranose (6) and (7), 3,5-di-O-acetyl-6-bromo-2,6-dideoxy-D-arabino-1,4-lactone (8), and 2,3,5,6-tetra-O-acetyl-1,4-anhydro-D-mannitol (9) have been measured at 270 MHz. Substantial differences are found for theR1-values of epimeric pairs of substances which can be used for structural evidence. The anomalousR1-values in deuteriochloroform for the H-2, H-3, and H-4 resonances of1are discussed.

ISSN:0008-4042    

DOI:10.1139/v80-306

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The1H nuclear magnetic resonance spectra obtained during the addition of amines to 4-acetyl-1-methylpyridinium iodide in aqueous solution provide data for the kinetic parameters associated with: (1) the rapid equilibrium of the addition step to form the carbinolamine intermediate; (2) the rate determining dehydration step to form thesynandantiimines; and (3) theantitosynisomerization. Depending on the amine used, (1) can result in methyl proton exchange that is either fast or slow relative to the chemical shift between the acetyl-CH3resonance of 4-acetyl-1-methylpyridinium iodide and the corresponding one due to carbinolamine. The line width data and the equilibrium constantKn, which is determined by flow uv, provide values for the rate constants (knandk−n) of the forward and reverse steps of the equilibrium. The logarithm ofkndoes not correlate with logKnor pKaof the amines. In addition, the enthalpy change ΔHfor the equilibrium step is found not to depend significantly on the nature of the amine. It remains relatively constant at about −11 kcal M−1. The dehydration step is subject to general acid and base catalysis with the effect decreasing in the order hydrazine, hydroxylamine, semicarbazide, and methoxyamine. For hydrazine and hydroxylamine, thesyn/antiratios are pH dependent. For hydrazine and semicarbazide theantitosynimine conversion depends on pH. The occurrence ofantitosynisomerism indicates that the dehydration of carbinolamine gives theantiimine as the product of kinetic control.

ISSN:0008-4042    

DOI:10.1139/v80-307

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Competition reactions using dimethylketene (DMK) – aluminum chloride complexes on a variety of substituted benzene derivatives gave partial rate factors. The logs of thesePfxvalues when plotted versus σ+values gave two line segments of ρ = −6.59 for less active substrates, and ρ = −0.92 for more active substrates. Similar results were found for diphenylketene (ρ = −9.47 and −1.07).These results were rationalized by analogy to vinyl cation alkylations. A pair of π complexes (outer then inner) occur between initial approach of the reagent and final, product-determining π-complex formation. In one of these complexes the C=C bond of the ketene complex may be able to back-bond in a manner similar to that found in inorganic complexes of CO and metals.

ISSN:0008-4042    

DOI:10.1139/v80-308

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

An alternative two-dimensional nmr pulse sequence, (90°–t1/2–90°–t1/2–FID),correlates the chemical shifts of coupled nuclei. The application of this technique to the solution of the complicated proton nmr spectra of oligoribonucleotides is discussed.

ISSN:0008-4042    

DOI:10.1139/v80-309

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

2-Hydroxymethyl-3-methylquinoxaline-di-N-oxide (GS-7443) is rapidly metabolized in the chicken, rat, and dog to 3-carboxy-2-methylquinoxaline-1-oxide and a conjugate of 3-carboxy-2-methylquinoxaline-di-N-oxide. No appreciable amounts of other metabolites nor unchanged GS-7443 could be detected in the excreta from these animals. There were minor quantitative differences in the relative amounts of the two metabolites; moreover, the conjugating group employed by the chicken is different from that of the dog but the material being conjugated is the same. Although measurable tissue levels of drug-related material were noted in several organs of the chicken 6 day s after drug administration, all chicken tissues examined were cleared of radioactivity within 21 days.

ISSN:0008-4042    

DOI:10.1139/v80-310

出版商:NRC Research Press    

年代:1980

数据来源: NRC