摘要:

Antipyrine (AT) reacts with bromothymol blue (BTB) in dichloromethane (DCM), forming an ion pair of 1:1 stoichiometry. Chemical equilibrium has been demonstrated and the formation constants of the ion pair at various temperatures have been calculated spectrophotometrically. The thermodynamic parameters of the reaction are ΔH0 = −6994 cal/mol, ΔS0 = −11.05 cal/K mol, and.

ISSN:0008-4042    

DOI:10.1139/v87-380

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

To provide the necessary parameters required for the conformational analysis of poly(oligomethylene glycol-4,4′-biphenyl dicarboxylates), two model compounds related to the above polyesters have been synthesized and their structures established by X-ray diffraction. The crystal structures of ethylene glycol di-para-phenylbenzoate (2DPPB) and 1,4-butylene glycol di-para-phenylbenzoate (4DPPB) have been solved by direct methods. 2DPPB is monoclinic witha = 7.174(2) Å,b = 8.101(2) Å,c = 19.183(4) Å, β = 102.48(2)°,Z = 2, space groupP21/c. 4DPPB is triclinic witha = 9.978(2) Å,b = 11.172(3) Å,c = 11.437(2) Å, α = 85.46(2)°, β = 79.40(2)°, γ = 71.03(2)°,Z = 2, space group. The weighted least-squares refinements converged toRw = 0.054 (2DPPB) andRw = 0.057 (4DPPB). The values of ϵ, the tilt angle of the carboxylate group with respect to the phenylene ring, are 3.5° for 2DPPB and 1.5° and 1.4° for 4DPPB. A systematic study of this dihedral angle showed that the values of ϵ remain in the vicinity of 0°–10° and the value observed most frequently is 5°. The values of Φ, the dihedral angle between the two six-membered rings, are 36.2° in 2DPPB and 14.7° and 31.0° for 4DPPB. A systematic study with 71 biphenyl molecular fragments showed that distribution of Φ presents two maxima: one around 30° – 40° and the other in the range of 0°–10°. The conformation of the methylenic sequence is all-transfor 2BPPB and gtttt for 4DPPB.

ISSN:0008-4042    

DOI:10.1139/v87-381

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The interface between the water (1) – ethanol (2) system and silicone oil was studied over the whole composition range of the aqueous mixtures by means of adsorption and ellipticity measurements. The adsorbed layer was treated as a phase and, after derelativization of the relative surface excess, the adsorption isotherm (in term of molar fractions) as well as the activity coefficients of water and ethanol were calculated. From the above results and by analysing the ellipticity coefficient, we calculated the contribution to this latter due to the anisotropy of the adsorbed layer; the resulting "polynomial of anisotropy" was analyzed as a consequence of water and ethanol reorientations as the surface composition is changed.

ISSN:0008-4042    

DOI:10.1139/v87-382

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Complexes of the general formula [HgX2(Me3MCH2SeMe)]2, where M = Si, Ge; X = Cl, Br, I, have been prepared and characterized by1H nuclear magnetic resonance and Raman spectroscopy. Crystal structures of [HgX2(Me3SiCH2SeMe)]2, where X = Cl, Br, and I (1,2, and3respectively), show that they have centrosymmetric dinuclear structures. The crystals of1and2are monoclinic, while those of3are triclinic. For1:P21/c,a = 14.235(11),b = 6.551(6),c = 14.211(9) Å, β = 117.33(5)°,Z = 2, andR = 0.0560. For2:P21/c,a = 14.329(6),b = 6.695(2),c = 14.819(4) Å, β = 118.47(2)°,Z = 2, andR = 0.0540. For3:,a = 7.651(2),b = 8.387(2),c = 12.321(4) Å, α = 90.07(2), β = 91.80(2), γ = 116.02(2)°,Z = 1, andR = 0.0565. All three complexes show the expected pseudotetrahedral geometry about mercury. The stereochemical differences arise in the arrangement of the bulky trimethylsilylmethyl groups, which in the HgI2adduct are rotated away from the centre of the molecule but which in the HgCl2and HgBr2adducts are turned towards the centre. These are the first dinuclear structures reported of HgBr2and HgI2adducts since it was demonstrated 46 years ago by Evansetal. that [HgBr2(AsBu3)]2was present in [HgBr2(AsBu3)2•HgBr2].

ISSN:0008-4042    

DOI:10.1139/v87-383

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The photosensitized (electron transfer) irradiation of several conjugated 1,1-diphenyl alkenes, in acetonitrile with 1,4-dicyanobenzene or 1-cyanonapthalene as electron accepting sensitizer and 2,6-lutidine as base, leads essentially quantitatively to tautomerization to the less stable unconjugated isomer(s). The proposed mechanism for this reaction involves formation of the alkene radical cation and sensitizer radical anion followed by deprotonation of the radical cation, reduction of the resulting radical to the ambident anion by back electron transfer from the radical anion, and reprotonation. There are several steps in this mechanism that could control the ratio of isomers. Evidence is provided that, at least in some cases, it is the relative rate of deprotonation from the isomeric radical cations that is the determining factor. This rate is influenced by the conformation of the radical cation; the carbon–hydrogen bond involved in the deprotonation step must overlap with the singly occupied molecular orbital.

ISSN:0008-4042    

DOI:10.1139/v87-384

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The 14-membered lactone, 13-tetradecanolide, can be alkylated to give mainly the 2R*, 13S*-dimethyltridecanolide. A second alkylation gives the 2,2-dimethyl lactone. The conformation of the starting material and alkylation products exist in the regular [3434] conformation. This model is used to rationalize the stereochemical outcome of the reaction and suggest the conformation of the intermediate enolate.

ISSN:0008-4042    

DOI:10.1139/v87-385

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v87-386

出版商:NRC Research Press    

年代:1987

数据来源: NRC