摘要:

The concept of monotonicity of entropy production is discussed regarding its application to chemically reacting systems. It is concluded that the concept cannot be generally applied even to elementary reactions in ideal homogeneous systems.

ISSN:0008-4042    

DOI:10.1139/v76-286

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Derivatives of the carboxylic acids RCOCH2CH(OCH3)COOH and RCOCH=CHCOOH (R = Me,i-Bu, ortert-Bu) have been identified among the major methanolysis products of three 1,1,1-trichloro-2-hydroxy-4-alkanones, RCOCH2CH(OH)CCl3. In addition, β-methoxy esters RCOCH(OCH3)CH2COOCH3are obtained if hydrogen atoms are present at the alkyl carbon directly attached to the carbonyl group (R = Me ori-Bu). 1,1,1-Trichloro-2-hydroxy-4-pentanone (1) yields the known methyl 5-chloro-2,4-pentadienoate (9) as a minor by-product. An α,α-dichloro epoxide (15) is postulated as the key intermediate in the methanolysis mechanism leading to the β-methoxy esters.

ISSN:0008-4042    

DOI:10.1139/v76-287

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The isoelectronic series lead tetraacetate–hydrogen fluoride, lead tetraacetate, thallium(III) acetate, and mercuric acetate were used to oxidize the bicyclic olefin dibenzobicyclo[2.2.2]octatriene. The stereochemistry of the products formed from these reactions substantiates the proposal that the first formed intermediate in these oxidations is thecis-molecular addition product of the metal and its ligand to the bicyclic olefin. Subsequent stereospecific rearrangement of the adducts in the case of the lead and thallium reagents verified the absence of the involvement of homolytic processes in the formation or decomposition of the adducts.

ISSN:0008-4042    

DOI:10.1139/v76-288

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The free radical addition of iodine to dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (3a)yields three stereoisomeric dimethyl 3,5-diiodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes4–6), as well as dimethyl 5,6-diiodobicyclo[2.2.1]hept-2-ene-2,3-dicarboxylate (9). By-products are two dimethyl 3-hydroxy-5-iodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes7,8). Compounds4and5are also obtained as major products of addition of iodine to dimethyl tetracyclo[2.2.1.02,603,5]heptane-2,3-dicarboxylate (quadricyclane10a). The structures of these various products were elucidated with the aid of1H and13C nmr and high-resolution mass spectroscopy.

ISSN:0008-4042    

DOI:10.1139/v76-289

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The frequency ν(OH … N) of methanol complexes with substituted pyridines appears to be a sensitive detector of substituent effects on the basicity of pyridines in an apolar medium. The coefficients ρIand ρR, which respond to I and R effects and which are obtained from the Taft–Ehrenson equation, agree with those found for the pKaof pyridinium ions for the three substitution positions. Those values which are observed to diverge are explained by the much greater electron attracting power of the azonium group compared to that of the aza group. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v76-290

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Crystals of tetraammonium diphosphate, (NH4)4P2O7, crystallize in the monoclinic system with space groupC2/c,Z = 4 and lattice parametersa = 11.758(3),b = 6.486(2),c = 13.659(2) Å and β = 104.81(1)°. The structure was refined using full-matrix least-squares methods with 810 reflections to anRvalue of 0.092. The diphosphate anion contains a crystallographic two-fold axis, and has a configuration intermediate between staggered and eclipsed. The bridging P—O bond length is 1.624(2) Å and the terminal P—O bonds average 1.507 Å. The diphosphate groups lie in sheets defined byand are bridged by NH4+groups which hydrogen bond to only the terminal oxygen atoms. Each hydrogen is bonded to one oxygen atom but each of the terminal oxygen atoms interacts with either two or three hydrogen atoms.

ISSN:0008-4042    

DOI:10.1139/v76-291

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The H2and CH4chemical ionization mass spectra of formate esters up to the butyl formates have been determined. Deuterium labelling of the ester and deuterated reagent gases have been used to establish reaction mechanisms. The major fragmentation reactions of the protonated molecular ion areReaction (a) is the dominant fragmentation for methyl formate, (b) is the dominant fragmentation for ethyl formate, while (c) is the dominant fragmentation for higher formate esters. The results show that the relative importance of the fragmentation routes cannot be predicted from the enthalpy of reaction of ground state HCO2R.H+but are determined by the fragmentation rate coefficients averaged over the appropriate internal energy distribution of the excited HCO2R.H+ions.

ISSN:0008-4042    

DOI:10.1139/v76-292

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

In the family of mutually interconvertible δ-O-methyl-deoxynitroinositols having themyo-5 (1),neo-2 (2),allo-5 (3),epi-1 (4),epi-6 (5), andcis(6)configurations the relative thermodynamic stabilities of the individual members and of the three corresponding sodium nitronates1′,3′, and5′ were assessed by determining equilibria of epimerization at pH8.2 and pH > 12. The orders of stability areand1′ > 3′ > 5′. The equilibrium data, together with those previously obtained for the stereoisomeric series comprising the correspondingscyllo(7),myo-1 (8),epi-3 (9), andmuco-3 (10) epimers and their nitronates7′,8′, and9′, were compared with theoretical values that were obtained from calculated conformational energies. The non-bonded interactions of the nitro and the nitronate group were evaluated and variable energy parameters were devised on the basis of differinggauchearrangements.

ISSN:0008-4042    

DOI:10.1139/v76-293

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The quantitative importance (several ppm) of the effect of solute–solvent van der Waals' interactions on the13C chemical shift is shown for a non polar solute,n-pentane, in solution in 17 solvents and in the gas phase. The van der Waals screening constant term is discussed in respect to several theoretical functions of the solvent refractive index. The extension to the case of13C of the solvent parameter scale which characterises the van der Waals interactions in19F nmr explains quantitatively this phenomenon and allows the separation of the anisotropic term in the case of C6H6. This parameter scale is extended to several solvents. The linear variation of this van der Waals effect on the chemical shift in terms of the volume fraction is interpreted leading to a relationship which allows calculation of this parameter for a solvent mixture. The variation of the sensitivity to this effect of the different magnetic sites depending on their position in the carbon chain is discussed. The theoretical expression of the site factor leads only to a qualitative explanation of this variation.

ISSN:0008-4042    

DOI:10.1139/v76-294

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Phytol has been incorporated into lecithin bilayers.13C spin–lattice relaxation times, which have been measured for both components of the model membrane, indicate a marked destabilization of the bilayer due to intercalated phytol. The disruption of normal phospholipid packing is due to the highly branched nature of the phytyl hydrocarbon chain. In addition, the position of phytol in the bilayer has been determined by means of a linear electric field effect of the polar lipid head group upon the13C chemical shifts of the phytol olefinic carbons.

ISSN:0008-4042    

DOI:10.1139/v76-295

出版商:NRC Research Press    

年代:1976

数据来源: NRC