摘要:

The number of structural isomers obtainable from all possible substitutions in an alicyclic hydrocarbon is found by the use of Burnside's Lemma. Four classes of compounds exist according to the number of vertices of the ring, and the number and type of substituents on the carbons. The theory is also applicable to other types of compounds in which paired substituents occur,e.g. in the biologically-synthesisable porphyrins. Where the pairing is not mandatory, Polya's Theorem is utilized for enumeration. Examples are provided for each of the classes of compounds.

ISSN:0008-4042    

DOI:10.1139/v77-385

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A quantitative perturbational molecular orbital (PMO) analysis has been performed onab initioSCF-MO wavefunctions associated with the rotation of the methyl groups in a series of (CH3)2X molecules (X = CH2, O, S, C=O, C=CH2). Two fragmentation modes have been investigated: Methoda, in which the system is dissected into X and (CH3)2; and Methodb, in which the system is dissected into CH3X and CH3. Both fragmentation modes reproduce the principal property of these molecules, viz., that the more crowdedSSconformation is preferred. However, whether this conformational preference is controlled by two-electron stabilizing effects or four-electron destabilizing effects is found to depend upon both the mode of fragmentation and the nature of the substituent X. The quantitative results are supplemented by a detailed qualitative description of the nature of the group orbitals associated with the two fragmentation modes and the various types of orbital interactions. It is shown that orbital energy differences control the qualitative discussion of Methoda, and overlap effects control that of Methodb. Although the final result, i.e., the preference for theSSconformation, and the behaviour of individual orbital interactions are anticipated correctly by the qualitative arguments, these are unable to assess the relative contributions of the stabilizing and destabilizing interactions.

ISSN:0008-4042    

DOI:10.1139/v77-386

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The structure of [RuCl3(NH3)3] prepared from the blue chloro-ammine complex of ruthenium is described. The crystals are orthorhombic,a = 9.933(3),b = 6.522(2),c = 5.475(2) Å,Z = 2, space groupPmn21. The structure analysis used 283 observed reflections, whose intensity was measured on a Picker FACS-1 diffractometer. The structure was refined (full-matrix) toR = 0.029. The crystal is composed of chains offac-[RuCl3(NH3)3], and is disordered, approximately 10% of the chains being reversed in direction and displaced one-half in z. The Ru–ligand distances and angles are normal.

ISSN:0008-4042    

DOI:10.1139/v77-387

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

From a determination of the phase diagrams, at 25 °C, the following double salts were shown to exist: 3LiCl•InCl3•8H2O in the system LiCl–InCl3–H2O, 2KCl•InCl3•H2O and 3KCl•InCl3•2H2O in the system KCl–InCl3–H2O, 2RbCI•InCl3•H2O in the system RbCl–InCl3–H2O, 2CsCl•InCl3•H2O in the system CsCl–InCl3–H2O, 2NH4Cl•InCl3•H2O in the system NH4Cl–InCl3–H2O, In2(SO4)3•InCl3•(17 ± 1)H2O in the system In2(SO4)3–InCl3–H2O. No double salt was found in the system NaCl–InCl3–H2O, studied previously (1). All the double salts except the two involving potassium chloride are congruently saturating at 25 °C.

ISSN:0008-4042    

DOI:10.1139/v77-388

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A polarographic study of the oxidation mechanism ofL-ascorbic acid and of the reduction mechanism of dehydro-L-ascorbic acid was carried out in an acid medium.ForL-ascorbic acid, the oxidation process involves a two electron transfer and obeys the overall reactionThe polarographic curve shows that the limiting current is governed by diffusion. On the rising portion of the wave, the two electron oxidation process consists of two consecutive one electron transfers, the second being the rate determining step (rds). The reaction orders, together with the Tafel slopes, were calculated.The reduction of dehydro-L-ascorbic acid at the limiting current is kinetically controlled and involves a two electron transfer. The reaction kinetic pathways were studied and the reaction orders and Tafel slope were calculated. It is deduced that, for low overvoltages, the second one electron transfer is the rate determining step.

ISSN:0008-4042    

DOI:10.1139/v77-389

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Complex formation between sulfur dioxide and iodide ions in acetonitrile (AN) has been studied by vapour pressure measurements. The enthalpy changes ΔH0for 1:1 association reactions between SO2and halide (X−) ions in AN and between SO2and Cl−in dimethylsulfoxide (DMSO) have been determined at 25 °C by calorimetry. The ΔH0values (kcal mol−1) are respectively −4.1 (Cl−), −3.4 (Br−), −3.0 (I−) in AN and −0.7 (Cl−) in DMSO. In contrast to previous literature data there is a linear relationship between these ΔH0and reported ΔG0values for the formation of the SO2X−complexes in AN. The difference between the ΔH0values for SO2Cl−in the solvents AN and DMSO is accounted for by the more exothermic enthalpy of solution of SO2in DMSO which is the more basic solvent, and by the expected minor difference in the enthalpies of transfer of Cl−and SO2Cl−from AN to DMSO, both dipolar aprotic solvents. Some of the problems connected with the stability order of the SO2X−complexes are discussed in relation to solvent effects and properties of X−.

ISSN:0008-4042    

DOI:10.1139/v77-390

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Substituent parameters were derived for the semiempirical determination of13C chemical shifts in saturated hydrocarbons, alcohols, amines, ketones, and olefins. The olefin parameters are valid for six-membered rings and the remaining parameters for six-membered rings in chair conformations. The use of these parameters for the calculation of carbon resonances is illustrated with a number of examples.

ISSN:0008-4042    

DOI:10.1139/v77-391

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The various effects (α, β, γ and δ) on the13C nmr of azido steroids have been measured. For cyclohexane azides constrained to equatorial and axial configurations, the α-effects were determined to be 33.6 and 31.2 ppm. Both γ- and δ-effects have magnitudes near those for OH and NH2groups. On the other hand, the β-effect of the azides is slightly smaller than those of hydroxyls or amines as its magnitude is reduced by a γ-effect of the second nitrogen atom of the azide group. This additional γ-effect is a function of the spatial arrangement of the Cβ—H bond with respect to the azide group. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v77-392

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The observed and calculated, negative, long-range spin–spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominants-cisplanar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.

ISSN:0008-4042    

DOI:10.1139/v77-393

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Physciosporin, a new chlorinated depsidone, has been isolated from the lichenPseudocyphellaria physciosporaand identified as methyl 2-chloro-4-formyl-3,8-dihydroxy-1,6,9-trimethyl-11-oxo-11H-dibenzo[b,e][1,4]dioxepin-7-carboxylate (methyl 5-chlorovirensate),1.

ISSN:0008-4042    

DOI:10.1139/v77-394

出版商:NRC Research Press    

年代:1977

数据来源: NRC