摘要:

The (n − 1)-fold degenerate set of transition probabilities used in our recent reformulation of unimolecular reaction theory is operationally equivalent to the set of effective strong-transition probabilities introduced recently by Nordholm. We have found that the relaxation matrix corresponding to these transition probabilities commutes withanyother relaxation matrix which will drive the same system to a Boltzmann distribution at infinite time. Some useful results stemming from this commutative property are presented; we expect that these results will help to clarify further the nature of the assumptions underlying strong- and effective strong-collision theories.

ISSN:0008-4042    

DOI:10.1139/v79-452

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

We have used a flow calorimeter and a flow densimeter for measurements at 25 °C of heat capacities and densities of aqueous solutions of four electrolytes of high charge type: LaCl3, Cr(NO3)3, K3Fe(CN)6, and K4Fe(CN)6. Results of these measurements have been used for calculating corresponding apparent molar heat capacities and apparent molar volumes, which have been extrapolated to infinite dilution to obtain the corresponding standard state apparent molar and partial molar properties. Uncertainties resulting from extrapolations of heat capacities are discussed. Results of our measurements are compared with those of earlier related investigations.

ISSN:0008-4042    

DOI:10.1139/v79-453

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v79-454

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The direct (Φ6 = 0.04) or acetone sensitized (Φ6 = 0.51) photolysis of 2-cyano-1,4-dihydro-1,4-ethanonaphthalene (5) yields 1-cyanobenzotricyclo[3.3.0.02,8]octa-3-ene (6). Deuterium labelling studies suggest that6derives from a Zimmerman di-π-methane rearrangement and not from the McCullough 1-cyanocyclohexene rearrangement. The observed rearrangement and regioselectivity are in accord with predictions based upon CNDO-CI calculations of changes in atom–atom interaction energies on excitation to theS1andT1excited states of5.

ISSN:0008-4042    

DOI:10.1139/v79-455

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Transient absorptions in the range 380–500 nm in deoxybenzoin are investigated for the first time by nanosecond laser spectroscopy. This study gives evidence for absorption by a triplet state, and by benzoyl and benzyl radicals. Photoreduction of the triplet state and generation of a ketyl radical are also obtained. This enables some peculiar results of the polymerization of vinyl monomers photoinduced by deoxybenzoin to be explained. Our results show that deoxybenzoin exhibits a peculiar behaviour since the two photoprocesses occur with the same efficiency. Hydrogen abstraction and α-cleavage rate constants, quenching rate constants of the species by oxygen, lifetimes of the transients, and absorption spectra are derived. The influence of the solvent is discussed as a function of the excited states involved. A complete diagram of the evolution of the energy levels is thus obtained.

ISSN:0008-4042    

DOI:10.1139/v79-456

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

3-O-benzyl-1,2-isopropylidene-α-D-xylo-pentodialdofuranose could not be α-methylated by direct or indirect methods. The aldol product from reaction of the dialdofuranose with formaldehyde could not be trapped, but underwent a Cannizzaro reaction to give theC-4-bis-hydroxymethyl product. The latter can be regioselectively sulfonated at the pro-(S) hydroxymethyl group. Reduction with lithium aluminum hydride then affords 3-O-benzyl-1,2-isopropylidene-4-C-methyl-α-D-xylo-furanose as the major isomer, the configuration of which is proved by transformation into an oxetane.

ISSN:0008-4042    

DOI:10.1139/v79-457

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The cyano group effect on diastereoselectivity is studied through the reduction ofcisandtrans3-R4-cyano cyclohexanones with NaBH4; the diastereoselectivity (zero for R = H) is 74 and 62% respectively (R = CH3) and 74 and 50% (R = (CH3)3C), the more stable isomer being always the major one. These stereoselectivities are rationalized from the experimental values of free enthalpy between conformers and from the diastereoselectivities of the 3-t-butyl (and 4-t-butyl) cyclohexanones,cis3,5-dimethyl and 3,3,5-trimethyl cyclohexanones, without taking account of a cyano group specific effect. The decrease in diastereoselectivity for R = (CH3)3C (transisomer) is associated with deformation induced by steric strain between the substituents.

ISSN:0008-4042    

DOI:10.1139/v79-458

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Gaseous protonated acids fragment in the first drift region of a double focussing mass spectrometer to yield the corresponding acylium ion and water. The metastable peaks for this fragmentation reaction have been recorded for the protonated acids from acetic to valeric and the kinetic energy release distributions evaluated from the metastable peak shapes. The protonated acids were produced by dissociative ionization of the ethyl, propyl, and butyl esters. The results provide evidence for two structures for gaseous protonated acids. Fragmentation of the hydroxyl protonated structure, a minor contributor to the metastable peak intensity, shows a low kinetic energy release (T(most probable) = 0.02 eV) as would be expected for a simple bond fission reaction. Fragmentation of the carbonyl protonated acid, which represents the major part of the metastable peak, is accompanied by a muchlarger kinetic energy release (T(most probable) = 0.30 to 0.43 eV). This result is interpreted in terms of an activation barrier for fragmentation of the carbonyl protonated acid which is considerably greater than the reaction endothermicity, with the excess energy being partitioned between internal energy and kinetic energy of the fragments. The results indicate that the addition of the acylium ion to water in the gas phase to produce the carbonyl protonated acid has an activation energy barrier.

ISSN:0008-4042    

DOI:10.1139/v79-459

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The thermal decomposition of 1-(2-cyano-2′-propoxy)-4-oxo-2,2,6,6-tetramethylpiperidine in solution has been studied as a function of solvent, temperature, and the presence of radical scavengers. In the absence of a scavenger, decomposition produces a hydroxylamine and methacrylonitrile, whereas in the presence of a scavenger such as oxygen, a nitroxide and 2-cyano-2-propyl radicals result. Decomposition in the presence of a scavenger is ∼50 times more rapid than decomposition in its absence. By using various free radical scavengers, scission of the NO—C bond is confirmed, that is the reverse of the normal nitroxide–alkyl radical reaction. Increasing solvent polarity causes a marked decrease in thermal stability, both in the presence or absence of radical traps. The importance of the thermal decomposition reactions in the interpretation of nitroxide scavenging of radicals is discussed.

ISSN:0008-4042    

DOI:10.1139/v79-460

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Dielectric absorption studies have been made on molecules of the typewhere X—Y is —OCH3, —COCH3, —CH2Cl, and —CH2CN. The molecules have been dissolved in (a) a polystyrene matrix and (b) in the viscous liquido-terphenyl. For 1,4-dimethoxybenzene the group process dominates in both media, and estimates have been made of the activation enthalpy for group relaxation. For 1,4-dimethoxybenzene in benzene, decalin, Nujol, ando-terphenyl solutions, however, there appears to be a small contribution from the molecular process. No such contribution was detected in the matrix studies on this solute molecule. For 1,4-diacetylbenzene, 1,4-bis(chloromethyl)benzene, and 1,4-bis(cyanomethyl)benzene ino-terphenyl solution it again seems that the group and molecular processes overlap. However, in polystyrene the enthalpies of activation which emerge are characteristic of the group relaxation process as determined by the nmr approach. Altogether, the work illustrates thato-terphenyl may be a useful solvent in helping to decide whether a solute has contributions from an intramolecular motion.

ISSN:0008-4042    

DOI:10.1139/v79-461

出版商:NRC Research Press    

年代:1979

数据来源: NRC