摘要:

Reactions of trifluoromethoxide ion, CF3O−, with carboxylic acids have been examined. Facile fluoride transfer is observed to occur to the acids and a subsequent fluoride transfer equilibrium established in mixtures of carboxylic acids. From the equilibrium constant obtained for fluoride transfer acetic acid and propionic acid are found to have near identical fluoride binding energies. Further reaction between the acid solvated fluoride ions and the carboxylic acids is observed to occur resulting in HF displacement and formation of bicarboxylate anions. In mixtures of acetic and propionic acids acetate and propionate anion transfer equilibria are again established. An analysis of the energetics for these processes reveals that propionic acid binds the carboxylate anions more strongly than acetic acid by 0.1 to 0.2 kcal/mol.

ISSN:0008-4042    

DOI:10.1139/v79-077

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A lyomesophase prepared from decylammorium tetrafluoroborate, ammonium tetrafluoroborate, and water, which orients in a magnetic field perpendicular to the directors (type II), has been investigated with respect to the isotopic composition, H2O/D2O of the aqueous compartment at constant overall chemical composition. An effect of the isotopic composition of the water has been discovered, which influences the packing of the water and tetrafluoroborate ions at the interface. An interface structure transition occurs at ∼ 14 mol% D2O in H2O. The ammonium ions, which do not form part of the first bound layer at the interface, are affected to a much smaller degree and the sudden changes in the direction of variation of nmr parameters are not observed for this ion. The interface structure at > 14 mol% D2O evidently does include more remote participation of NH4+ions.Recent low angle X-ray diffraction studies, available to us, indicate that the mesophases which orient in magnetic fields have two levels of structure, the packing of amphiphiles in discrete anisotropic micelles and the super-packing of the micelles themselves. These studies now enable us to reinterpret other similar thermally induced structural changes in the interface, from results previously encountered, in the decylammonium chloride system. It is possible to have changes in the packing of water, amphiphiles, and ions at the interface without changes in the superstructure. Such changes in interface packing might well go undetected in a measurement of bulk properties but are revealed by measurement of nmr parameters for the oriented mesophase of different species involved in the interface structure. The isotope effect on structural packing at the interface is absent in two other mesophases investigated.

ISSN:0008-4042    

DOI:10.1139/v79-078

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The platinum(II) complextrans-PtCl(PEt3)2(CH=NC6H4-p-CH3) gives 1:1 complexes with CdCl2, HgCl2, and AuCl and a 1:2trans-adduct with PdCl2, thus showing its character as a monodentate,N-ligand.

ISSN:0008-4042    

DOI:10.1139/v79-079

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Hypophosphorous, phosphorous, phosphoric, and arsenic acids, pure and their aqueous solutions were studied by ir spectroscopy. Strong continuous absorptions observed with the pure liquid acids and with solutions containing less than one water molecule per acid molecule demonstrate that acid–acid hydrogen bonds in these systems are easily polarizable. The discussion of the PO and AsO bands as well as the discussion of the structure of the continuum demonstrates, however, that the degree of asymmetry of the energy surfaces in these hydrogen bonds is relatively large. It is shown that extended networks of such bonds exist. Due to the polarizability of these bonds, the proton motion in these bonds is strongly correlated. With addition of water, easily polarizable acid–water hydrogen bonds (I)(II) are formed. The energy surfaces in these hydrogen bonds are similar to those in the acid–acid hydrogen bonds. With further addition of water, proton boundary structure II receives noticeable weight, i.e., the degree of asymmetry of the energy surfaces in these bonds decreases due to addition of water molecules. The degree of symmetry of the energy surfaces in the acid–water hydrogen bonds increases in the series arsenic, phosphoric, phosphorous, and hypophosphorous acid.

ISSN:0008-4042    

DOI:10.1139/v79-080

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

4,6-Dinitro-7-methoxybenzofuroxan (4) reacts with MeONa–MeOH or with Et2NH competitively by σ-complex formation and demethylation, by nucleophilic reaction at the aromatic and aliphatic carbon centers, respectively. Carbonate ion in CHCl3in the presence of 18-crown-6 polyether also results in rapid demethylation. The facile leaving group ability in these SN2 displacements is consistent with the large acidity constant of 4,6-dinitro-7-hydroxybenzofuroxan (pKaca. −3.7), i.e., 4pKunits stronger than picric acid. Some unusual features exhibited in the nmr spectral characteristics of the σ-complexes are accounted for in terms of stereoelectronic effects.

ISSN:0008-4042    

DOI:10.1139/v79-081

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A new treatment of the solvent effect on the solvolysis oftert-butyl chloride is proposed. This treatment is based on activation free energy measurements and on transfer free energy measurements of the reactant (R) on the one hand and of a model (M) of the activated complex (AC) on the other hand. Solute–solvent interaction free energies for the reactant, the activated complex and the model compound are estimated. This estimation involves the calculation of the free energy of cavity formation of these various solutes (R, AC, and M) in all the solvents. These cavity terms, which are a function of the cohesive properties of the solvent and of the surface of the cavity do not reflect the electronic structure of the solute whereas the interaction free energy term does. The method we propose can be described as a new 'experimental' approach for the study of the charge separation in an activated complex.

ISSN:0008-4042    

DOI:10.1139/v79-082

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

1H nmr spectroscopy has been used to demonstrate hydrogen–deuterium exchange in solutions of NaBH4/NaB2H4in diglyme and KBH4/KB2H4in 18-crown-6 ether/chloroform. Earlier observations of such exchange with LiBH4/LiB2H4in an ethereal solvent were confirmed. Spectra were simplified by broadband decoupling of deuterium, facilitating quantitative measurement of the degree of exchange.

ISSN:0008-4042    

DOI:10.1139/v79-083

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The equilibrium position and the kinetics of the extensive hydration of the title compound 1 have been investigated by spectroscopic (uv and nmr) techniques. The hydrate exists exclusively as the geometrically isomeric 1,3-phthalandiols and the hydration equilibrium constant is 7.7 ± 0.5 at 25 °C. From the temperature dependence of the equilibrium position, values of the enthalpy and entropy of hydration were calculated. The reaction is general acid – general base catalyzed; the Brønsted α and β coefficients are both near 0.5. Catalysis by Zn(II) is observed. The mechanism of the reaction (which probably proceeds via rate-determining formation of the normalgem-diol followed by rapid cyclization) is discussed.An analysis of the thermodynamic data for the hydration of a variety of carbonyl compounds reveals that the degree of hydration is normally determined by both enthalpy and entropy contributions to the free energy. However, the extensive hydration of1is determined solely by the enthalpy term. No hydration could be detected for benzaldehyde or the other isomeric dialdehydes.

ISSN:0008-4042    

DOI:10.1139/v79-084

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Excess heats of the following mixtures of trialkylamines and tetraalkyl tin compounds with branched and linear alkanes have been measured at 25 °C: five trialkylamines NR3(R = C2H5, C3H7, C4H9, C10H21, C12H25) with six linear alkanes,n-C5,n-C6,n-C8,n-C10,n-C12,n-C16, and three highly branched alkanes, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, and 2,2,4,4,6,8,8-heptamethylnonane (br-C16). Further measurements were carried out on tetrapropyl tin (SnPr4) withn-C8,n-C16, and br-C16.Measurements were made to obtain more information on the heats of disordering of long chain compounds and on an exothermic contribution to the heats coming possibly from the sterically hindered character of one of the components of the mixture. The three short-chain trialkylamines have large heats with the linear long alkanes and small heats with the branched alkanes. On the other hand, the two long-chain trialkylamines have very small heats with linear alkanes and large heats with the branched alkanes. These results are interpreted as indicating no change of liquid or solution 'structure' when two ordered compounds (long alkanes and long-chain amines) are mixed but a change of 'structure' when an ordered compound (long alkane or long-chain amine) is mixed with a non-ordered one (branched alkane or short-chain amine). The heat of disordering ofn-hexadecane is obtained with many order breakers and found to depend to some extent on the expansion coefficient of the order breaker.HEvalues for the series of the shorter NR3do not vary regularly with molecular weight but are smaller for the propyl (and possibly the ethyl) derivative. Similarly,HEof SnPr4inn-C16, br-C16, andn-C8are much lower than the corresponding heats with SnEt4and SnBut4. This is attributed to the presence of the exothermic contribution to the heats,HE(steric hindrance). TheX12parameter of the Flory theory has been calculated and is interpreted in terms of the disorder and steric hindrance contributions to the heats.

ISSN:0008-4042    

DOI:10.1139/v79-085

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

cis- andtrans-[Pt(pm)2X2] (where pm = 2-aminopyrimidine, 4-phenylpyrimidine, 4-methyl-pyrimidine and X = Cl, Br) were prepared and characterized. Theciscompounds were isolated from the reaction of K2PtCl4and pm in water, whiletrans-[Pt(pm)2X2] was obtained by isomerization ofcis-[Pt(pm)2X2] in dimethylsulfoxide. Thecis- andtrans-isomers react with thiourea (tu) to give different products (Kurnakov's test).The complexestrans-[Pt(pm)2(tu)2]X2were isolated and characterized.

ISSN:0008-4042    

DOI:10.1139/v79-086

出版商:NRC Research Press    

年代:1979

数据来源: NRC