摘要:

Available evidence suggests that (1) the stretching frequencies of highly-bent hydrogen bonds decrease with increasing temperature, regardless of whether the bonds are static or dynamic in character, to a single acceptor or to several competing acceptors; and (2) departures from symmetric trifurcation (or bifurcation) toward asymmetric situations lower the stretching frequency. In further support of these criteria isotopic probe ion spectra between 10 K and room temperature have been obtained for taurine and for trigonal (NH4)2MF6(M = Si, Ge, Sn, Ti). Evidence of a low-temperature transition at 100(10) K in trigonal (NH4)2SnF6is presented, and existence of the previously reported transition at 38.6 K in trigonal (NH4)2SiF6is confirmed. Symmetry changes associated with these transitions are discussed.

ISSN:0008-4042    

DOI:10.1139/v80-136

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A simple and convenient synthesis of tricyclic orthoester1(2,10,11-trioxatricyclo[4.4.4.01,6]tetradecane) is described.

ISSN:0008-4042    

DOI:10.1139/v80-137

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Mercaptide/alkoxide competition in substitution and addition reactions is discussed as it applies to the preparation of disulfides. Oxidation of an asymmetric disulfide with H2O2is shown to exhibit high regioselectivity which may be rationalized in the same terms employed for other sulfide oxidations, viz. substituent electron withdrawing ability (Xp) and steric effects.

ISSN:0008-4042    

DOI:10.1139/v80-138

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v80-139

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Errors reported in the literature on the migratory aptitudes of some aryl groups in triarylvinyl cations have been corrected. From the corrected as well as some new data, the relative migratory aptitudes for Ph: Tol: An in triarylvinyl cations in acetic acid media are calculated to be 1:4–5:162, based onkr(Tol)/kr(Ph)derived from migrations in the tritolylvinyl and 2-phenyl-1,2-ditolylvinyl cations andkr(An)/kr(Ph)derived from migrations in the 2-anisyl-1,2-diphenylvinyl and triphenylvinyl cations.

ISSN:0008-4042    

DOI:10.1139/v80-140

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Several tridentate ligands incorporating pyridine and substituted imidazoles were prepared and their physical properties studied as models for the enzyme carbonic anhydrase (CA). The H+and M2+binding abilities (pKaand) were determined. In the case of the imidazole ligands,N-methylation reduces the metal binding ability of the ligand by some 3–4units over the analogues in which the imidazole has N—H.1H-nmr studies of the simple ligands as a function of [Zn2+] show that the ligands are bound symmetrically as 1:1 and 2:1 complexes depending upon the ligand/metal ratio. Increasing the steric bulk of the ligands by introduction of 4,5-diisopropyl substituents on the imidazole inhibits the 2:1 (ligand/metal) complex. Titration experiments of several ligands bound to equimolar Zn2+and Co2+are described and analysed.

ISSN:0008-4042    

DOI:10.1139/v80-141

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Kinetics of the reaction between N(III) and Cl(V) have been studied in water and water–dioxan solutions. The rate equation of the reaction in each solvent could be written asand the rate rises as the dielectric constant of the medium is lowered. This observation is in accord with suggested mechanistic details involving the intermediate H2NClO5.

ISSN:0008-4042    

DOI:10.1139/v80-142

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Pulse nmr has been used to determine the temperature dependence ofT1at 9.2, 18, and 60 MHz and alsoT1ρat 9.2 MHz andT1Dat 18 MHz, for the proton resonance of solid acenaphthalene. The data indicate a discontinuity at ~130 K, coincident with the main thermal anomaly in the specific heat curve, and suggest the occurrence of two distinct molecular motions with activation energies 14.2 kJ mol−1and 18.9 kJ mol−1. Calculations using non-bonded atom–atom potential functions explain qualitatively the results of the nmr study and it is suggested that the two motional processes may be due to two sets of crystallographically different acenaphthalene molecules.

ISSN:0008-4042    

DOI:10.1139/v80-143

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The yield and13C content of the product C2F6were measured following the multiphoton infrared decomposition of CF3Cl. These factors were studied as a function of the activation frequency ω, of the pressure of CF3Cl, of the temperatureT, and of the incident energyE0. As in the case of CF3Br and CF3I the yield increases according toP2E02. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v80-144

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The first part of this paper describes the experimental search for a donor which would complex preferentially one of the isomers of 1,2-dicyanoethylene. This involved measuring the association constants (KcDA) of the charge-transfer (ct) complexes of several dimethoxynaphthalenes (DMN) with maleonitrile (MN) and fumaronitrile (FN). From the measuredKcDA, we found that MN complexes more strongly than FN with 1,4- and 1,5-DMN but that FN complexes more strongly with 2,3-DMN than does MN. These results are explained in terms of more than one favourable geometry for the ct complexes, since the donors are relatively large compared to the acceptors.Irradiation of the ct complexes between 1,4-, 1,5-, or 2,3-DMN and 1,2-dicyanoethylene led to isomerization of the olefins. The photostationary state depends on the absorption spectra of the ct complexes formed between the donor and the isomeric olefins. From spectroscopic and photo-CIDNP studies, we find evidence that the isomerization in polar solvents takes place via the triplet state of the olefin. The triplet is formed from the radical ion pair resulting after excitation of the ct complex.

ISSN:0008-4042    

DOI:10.1139/v80-145

出版商:NRC Research Press    

年代:1980

数据来源: NRC