摘要:

The thermal decomposition of 95:5 mixtures of trifluoroacetaldehyde (TFA) and di-tert-butyl peroxide (DTBP) has been studied at 100 Torr over the temperature range of 390 to 440 K. The major decomposition products included CO, CF3H, CH3COCH3, and CH4while C2F6, CF3CHOHCH3, CF3CH3, CF3COCH3, C2H6, (CF3)2CHOH, and H2were also found. In addition to the usual reactions for TFA thermal decomposition, reactions of methyl radicals with TFA to form isopropoxyl radicals were found. The alcohol products result from H atom abstraction reactions of the isopropoxyl radicals while CF3COCH3is a decomposition product. Arrhenius parameters for several reactions were determined: for DTBP decomposition, logk = 15.82 − 37.73/2.303RT; for H abstraction from TFA by CH3, logk = 8.30 − 7.37/2.303RT; for H abstraction from TFA by CF3, logk = 8.98 − 8.61/2.303RT. Consideration has also been given to several rate constant ratios for the formation and decomposition of isopropoxyl radicals.A study of the reaction order for the formation of CF3H, C2F6, and CH4showed that the orders were 3/2, 1, and 1 respectively for these three products. A reaction mechanism involving 14 individual steps is proposed to explain the reaction products and the observed orders of reaction.

ISSN:0008-4042    

DOI:10.1139/v79-353

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Heats of mixing,HE, of aniline + benzene at 298.15 and 308.15 K have been measured over the entire composition range. The results have been analysed in terms of Barker's and ideal associated model theory of non-electrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AB, AB2, A2B2, and B molecular species well describes (within ± 120 J/mol at the worst) the general behaviour ofHEwithxB(mole fraction of aniline) over the whole composition range for aniline + benzene mixtures. The equilibrium constants for the various association reactions along with the enthalpy of formation of various molecular species have also been calculated.

ISSN:0008-4042    

DOI:10.1139/v79-354

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The synthesis and crystal and molecular structure of the chloroperchloratotri(o-tolyl)phosphinemercury(II) dimer are reported. The compound [HgP(o-tolyl)3ClClO4]2belongs to the orthorhombic space groupPbcawitha = 12.218(2),b = 13.814(2),c = 26.074(3) Å, andZ = 4. The structure was refined to a finalRof 0.046 for 2584 reflections measured by diffractometer. The crystal structure consists of discrete centrosymmetric dimeric molecules of [HgP(o-tolyl)3ClClO4]2separated by normal van der Waals distances. The unique mercury atom forms two strong bonds (Hg—P 2.395(3), Hg—Cl(1) 2.332(4) Å) which deviate from linearity (P—Hg—Cl 164.1(1)°) and two weak bonds (Hg—O(1) 2.73(2) to the perchlorato group, Hg—Cl(1 *) 3.109(4) Å linking the mercury atoms about centers of symmetry). The four-fold coordination geometry about each mercury can be described as trigonal bipyramidal with the phosphorus and Cl(1) axial, and one equatorial site unoccupied. Intramolecular interactions are discussed with the assistance of cone angle calculations and a ligand profile for P(o-tolyl)3(θ = 198°). Vibrational and31P nmr spectra data are also presented for [HgP(o-tolyl)3ClClO4]2.

ISSN:0008-4042    

DOI:10.1139/v79-355

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Extended ligand–ligand repulsion calculations have been applied to a number of six coordinate organotin complexes of the type RR′Sn(bidentate)2(R, R′ = Me, Ph, Cl). Qualitatively, the calculations readily predict the decrease in the R—Sn—R′ angle with decrease in bite size of the bidentate ligand. The steric calculations are generally successful in predicting both thecis–transpreference of the R groups and the bond angles about the Sn atom. For the Me2Sn complexes, electronic effects (as expressed by Bent's rule) sometimes have to be used in conjunction with the steric calculations to rationalize the observed stereochemistry.

ISSN:0008-4042    

DOI:10.1139/v79-356

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The synthesis of all isomeric mono- and disilyl derivatives of cytidine, guanosine, and theirN-benzoyl analogues using thetert-butyldimethylsilyl protecting group is described. These compounds and those containing a 5′-monomethoxytrityl group have been condensed via the phosphodichloridite procedure to produce nucleotides rapidly and in good yields. The synthesis of 2′–5′-linked nucleotides is described. A cautionary note is introduced in regard to the preparation of 5′-monomethoxytritylguanosine and a novel methanolysis of certainN-benzoylcytidines is mentioned.

ISSN:0008-4042    

DOI:10.1139/v79-357

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The barriers to rotation about the N—CO bonds in a series ofN-vinyl amides have been determined by a study of their proton spectra at variable temperatures. A complete LACN 3 analysis of compound1gave the parameters used in a complete line shape (CLS) analysis to obtain ΔG≠. A new approximate method was shown to give a value for ΔGthat agreed within 0.1 kcal/mol of that obtained by CLS. The approximate method was employed to determine ΔG≠for other members of the series. The barrier in theN-vinyl amide1was found to be 2.5 kcal/mol higher than that in its saturated analog. Variations within the series ofN-vinyl amides amounted to only 1.2 kcal/mol. A steric effect is proposed for the increase in barrier height. The new approximation formula was tested for the general case of unequal singlet coalescence and found to givek's accurate to within 4% for Δν > 10 and to within 10% at lower values of Δν.

ISSN:0008-4042    

DOI:10.1139/v79-358

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The influence of a range of protic and aprotic solvents of varying polarities on the enantiomeric specificity of α-chymotrypsin has been examined using methyl (2S)- and (2R)-2-acetamido-2-phenylacetate (1) as representativeL- andD-substrates. The rates of hydrolysis were determined in solutions containing up to 30% organic solvent. The addition of organic solvent reduced the overall rates of hydrolysis of (2S)- and (2R)-1in each case, with those of theL-enantiomer (2S)-1being affected more than those of theD-stereoisomer (2R)-1. However, the enzyme overwhelmingly retains its normalL-enantiomeric preference under all conditions surveyed. It is concluded that α-chymotrypsin, and possibly other strongly stereospecific enzymes, can be used with confidence for asymmetric synthesis or resolution purposes in aqueous solutions to which moderate (up to 40%) proportions of organic cosolvents have been added to increase solubility of hydrophobic organic substrates.

ISSN:0008-4042    

DOI:10.1139/v79-359

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A total synthesis of (±)-isolongifolene6, a C15hydrocarbon derived from the acid-catalyzed rearrangement of the sesquiterpenoid longifolene, is described. The known carbomethoxyoctalone10was transformed via a 10-step sequence into the unsaturated keto tosylate9. The key step of the overall synthesis involved the efficient intramolecular γ alkylation of9to produce the tricyclic α,β-unsaturated ketone5. The latter compound was converted into the enone33, which had previously served as a precursor for the synthesis of (±)-isolongifolene6.

ISSN:0008-4042    

DOI:10.1139/v79-360

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

This work provides a study of the 1a2uπ, 2e2gσ, and 1e1gπ levels of a series of C6F5X compounds (X = F, Cl, Br, I, H, CH3) using ultraviolet photoelectron spectroscopy or more simply PES. The three levels are assigned from the PES spectra using the perfluoro effect. A correlation between the energies of these levels and the energies predicted by CNDO/2 and INDO is presented.

ISSN:0008-4042    

DOI:10.1139/v79-361

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The hydrolysis of coumarin diethyl acetal to coumarin proceeds via two detectable intermediates. A short-lived transient is observed in strongly acidic solutions (pH < 2.5); this is the oxocarbonium ion intermediate of the hydrolysis. That this cation can be detected suggests unusual stability, a fact which can be explained in terms of its pyrilium ion nature. A long-lived intermediate is also observed; kinetic and spectral evidence suggest that this is coumarinic acid ethyl ester. The lactonization of this ester shows a change in rate-determining step as the pH is varied. A corresponding change in products is found in the acetal hydrolysis, the coumarinic acid ester being the major product at high pH, with coumarin the major product at low pH. Both observations can be explained in terms of different modes of partitioning of cationic and neutral tetrahedral intermediates. Analysis in quantitative terms shows that the same tetrahedral intermediate is generated in the two different cases.

ISSN:0008-4042    

DOI:10.1139/v79-362

出版商:NRC Research Press    

年代:1979

数据来源: NRC