摘要:

Enthalpies of solution of 51 polar and nonpolar organic solutes have been determined in the solvent perfluoro-1,3-dimethylcyclo-hexane. The values have been combined with solute enthalpies of vaporization to give the enthalpies of transfer from vapor to solvent. These solvation enthalpies are for most solutes substantially less exothermic than those measured in other solvents. Polar interactions appear to be stronger than with hydrocarbon solvents; but this may result, in part, from incomplete dissociation of strongly associated solutes in the perfluoro solvent.

ISSN:0008-4042    

DOI:10.1139/v80-369

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The heat capacities of 25 liquid aliphatic, alicyclic, and aromatic ketones and aldehydes at 298.2 K and atmospheric pressure have been measured calorimetrically with a typical uncertainty of 0.5%. Additive parameters are proposed for estimatingCp(1) of ketones and aldehydes.

ISSN:0008-4042    

DOI:10.1139/v80-370

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The gas phase acidities of a series of fluorinated acetones and acetylfluoride have been determined. The results obtained are interpreted in terms of a model for fluorine substituents in planar carbanions in which fluorine exerts an overall stabilizing influence on enolate ions, but also has a component in the interaction which is destabilizing via a repulsive interaction between fluorine lone pair electrons and the carbanion centre. Comparisons with solution phase acidities are made and the validity of the model for fluorine substituents discussed.

ISSN:0008-4042    

DOI:10.1139/v80-371

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The formation constants of CdCl2, CdCl+, and Cd2+have been determined by polarography from 2.5 to 27.6 molar in HF/H2O.

ISSN:0008-4042    

DOI:10.1139/v80-372

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A series of dithiocarboxalato (X-dtb) complexes of molybdenum(IV), Mo(X-dtb)4, where theparasubstituent X = H, CH3, CH3O, F, C6H5, CHO, C6H5CO, or (n-C4H9)2N, the parent acids and tetraalkylammonium salts were studied by1H and13C nmr in order to monitor the expected charge density shifts as a function of the group X. Analysis of the13C nmr data unexpectedly revealed an absence of delocalization of electron density either from molybdenum to ligand or from ligand to molybdenum.

ISSN:0008-4042    

DOI:10.1139/v80-373

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The products (a benzoate ester or anN,N-dimethylbenzamide) have been accurately determined for the hydrolysis of theO-ethyl-N,N-dimethylbenzimidatonium ion (1) and its 4-nitro derivative (2) in dilute and moderately concentrated H2SO4solutions. In dilute acid the ratio of amide:ester is very small (0.0005–0.001). It is proposed that the ester product arises from the zwitterionic form of the tetrahedral intermediate of the hydrolysis. The small amount of amide is due to an SN2 hydrolysis reaction and to the non-catalyzed breakdown of the neutral form of the tetrahedral intermediate, the relative contributions of the two being unknown. Although ester remains the major product throughout, at some intermediate acid concentration (20% H2SO4for1and 35% H2SO4for2) a sharp increase in the amide:ester ratio is observed, followed by a levelling-off. This change is shown to be associated with tetrahedral intermediate partitioning, and not the SN2 reaction. It is argued that the strong acid product ratio represents the breakdown of the tetrahedral intermediate via cationic transition States. Two kinetically equivalent reactions are involved, the breakdown of theN-protonated tetrahedral intermediate producing a protonated ester and amine and the H+-catalyzed breakdown of the neutral tetrahedral intermediate producing a protonated amide and alcohol. Analogous pathways are also observed for the decomposition in acid of the amide acetals ArC(OMe)2NMe2, and the two systems are compared. A similar effect of the aromatic substituent on the partitioning ratio is noted, but the tetrahedral intermediate exhibits a greater tendency for amine expulsion. A kinetic analysis produces the estimate of 1011 s−1for the rate constant for the breakdown of the zwitterionic form of the tetrahedral intermediate. This very large rate explains why its decomposition remains important even in concentrated acids, where the amount of tetrahedral intermediate which actually exists as zwitterion must be extremely low.

ISSN:0008-4042    

DOI:10.1139/v80-374

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

3-18O-Testosterone (1) is transformed to estradiol (4) by human placental microsomes, and to the 6β- and 11α-hydroxy derivatives2and3byRhizopusarrhizus, without significant loss of label. Neither process is therefore one which involves reversible Schiff base formation at C-3 at any stage.

ISSN:0008-4042    

DOI:10.1139/v80-375

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The reactions of benzeneselenenyl chloride with three derivatives of tricyclo[4.2.2.02,5]deca-3,7-diene have been investigated in four solvent systems: methylene chloride, acetic acid, acetic acid/LiClO4, and methanol. Under conditions of kinetic control only products ofexo–antiattack upon the cyclobutene moiety are isolable when the solvent system is methylene chloride or acetic acid. This observation also holds in acetic acid/LiClO4except in the case of dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate where the major product is that of cross-bonding with solvent incorporation. In methanol products of solvent incorporation, transannular cross-bonding and lactonization (where possible) are observed. A general mechanistic scheme is proposed to account for these observations in accord with earlier results for the analogous arenesulphenylations.

ISSN:0008-4042    

DOI:10.1139/v80-376

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The1H nmr spectrum of tetrahydrothiophene has been analyzed. The best set of coupling values (Hz) is:,,,,,,,,(A and B refer to α-and β-protons and c and t denote respectively the same and opposite sides of the ring). The variances observed between the values of this set and those reported by Lozachetal., particularly the interchange of theandcouplings, are discussed and it is concluded that our set is the one that reproduces the most fine details of the spectrum profile. The proposed set has been selected as being the most physically meaningful, from amongst 24 equally valid sets of couplings, on the basis of a better agreement with theandvalues calculated from a Karplus relationship and from the INDO-FPT method respectively. In these calculations it was assumed that the molecule was interconverting rapidly (on the nmr time scale) between two puckered conformations withC2symmetry. A detailed discussion of the dependence of the couplings on the height of the pseudorotational barrier and on the temperature indicate that the minimum values of the potential energy correspond to these conformations.

ISSN:0008-4042    

DOI:10.1139/v80-377

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The synthesis of methyl 15-hydroxy-8(R)-methoxy-11(R)-p-nitrobenzoyloxy-9(S),12(R)-oxy-eicosa-13-ynoate, an arachidonic acid metabolite derivative, is described. As well, methods for the attachment of the C(13)—C(20) prostaglandin side-chain to furanosides were studied and the results are described. The reduction of the C-15 keto group on a model compound was performed and was found to have the same behavior as in the prostaglandins.A partial structure proof of Pace-Asciak's compound, 9,12-oxy-8,11,15-trihydroxy-13-enoic acid is given.

ISSN:0008-4042    

DOI:10.1139/v80-378

出版商:NRC Research Press    

年代:1980

数据来源: NRC