摘要:

An n.m.r. technique was used to measureKH/KDof ketal formation in methylene chloride solution for acetone and phenylacetone. For acetone,KH/KD = 0.95 per D for methyl ketal formation. Phenylacetone-1,1-d2, -3,3,3-d3, and -1,1,1,3,3-d5were examined for both dimethyl and ethylene ketal formation. For both ketals,KH/KD = 0.91 per D, for each ketone. Liquid scintillation counting was used to examineKH/KTfor ketal formation in methylene chloride. An extraordinarily large isotope effect was found for ethylene ketal formation in 1,3-diphenyl-acetone. HereKH/KT = 0.67 for one tritium atom. This isotope effect is too large to arise from hyperconjugative effects alone. It must have a substantial steric component.

ISSN:0008-4042    

DOI:10.1139/v75-505

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Kinetic isotope effects have been determined for the E2 reactions of a series of 2-phenylethyldimethylanilinium salts containing substituents in the aniline ring with sodium ethoxide in ethanol at 40 °C. The nitrogen isotope effect, (k14/k15−1)100, is not very sensitive to substituent changes but appears to increase slightly with increasing electron-withdrawing ability of the substituents,i.e., 1.19 ± 0.07, 1.13 ± 0.06, 1.12 ± 0.08, 1.30 ± 0.07, and 1.32 ± 0.06 forp-OCH3,p-CH3,p-H,p-Cl, and,m-CF3, respectively. The hydrogen–deuterium isotope effects pass through a minimum in the region of the unsubstituted compound and increase both with increasing electron-donating as well as with electron-withdrawing power of the substituents,i.e.kH/kD = 4.70 ± 0.06, 4.61 ± 0.04, 4.51 ± 0.04, 4.53 ± 0.09, 5.00 ± 0.07, and 5.39 ± 0.07 forp-OCH3,p-CH3,p-H,p-Cl,m-CF3, andp-CF3, respectively. The results are discussed in terms of recent theoretical treatments of the effect of structural variations in the reactants on the nature of the transition state of E2 elimination reactions. The conclusion is reached that the transition states in the present reaction series can be characterized as 'central with slight carbanion character' and that the effect of a change in the ability of the leaving group on the structure of the transition state manifests itself mainly in the direction perpendicular to the reaction coordinate. A simple novel hypothesis is formulated which emphasizes the importance of the location of the transition state in a More O'Ferrall-type potential energy diagram in determining its sensitivity to structural changes in the reactants.

ISSN:0008-4042    

DOI:10.1139/v75-506

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The reaction of α-mercaptoaldehydes and ketones with 1,3-butadien-1-yltriphenylphosphonium salts (4) unexpectedly leads to 3-vinylthiophenes and triphenylphosphine. This result is attributed to the retardation of the usual Wittig cyclization reaction which allows the competing reaction to occur.

ISSN:0008-4042    

DOI:10.1139/v75-507

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Measurements of the rate of the reactionwere made over the temperature range of 347 to 832 K and a pressure range of 140 to 739 N m−2. Experiments were carried out using a discharge fast-flow system with a fixed observation port. O atoms, generated by the N + NO→N2 + O reaction, were reacted with H2added downstream under pseudo first-order conditionsRelative O atom concentrations were determined using two independent methods: atomic resonance fluorescence at 130.6 nm and the air afterglow technique., The rate coefficients derived from our data can be expressed ask1 = (8.3 ± 3.8) × 10−12exp {−36.0 ± 2.0 kJ mol−1RT} cm3molecule−1s−1(by resonance fluorescence), andk1 = (8.8 ± 5.0) × 10−12exp {−34.9 ± 2.0 kJ mol−1/RT} cm3molecule−1s−1(by air afterglow method). Comparisons are made with selected published results.The Arrhenius plot of our data shows no evidence of curvature at low temperature.

ISSN:0008-4042    

DOI:10.1139/v75-508

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The molecular structure of tetramethylgermane has been determined by vapor phase electron diffraction. The structural parameters, based onrginteratomic distances arer(GeC) = 1.945 ± 0.003 Å,r(CH) = 1.12 ± 0.02 Å, andTetrahedral symmetry of the GeC4skeleton was preserved in the analysis by including a shrinkage correction for the C … C interatomic distance. The quoted uncertainties were estimated to include both systematic and random errors.

ISSN:0008-4042    

DOI:10.1139/v75-509

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Thiobinupharidine epimers possessing axial methyl groups at C-1 and C-1′ have been isolated from extracts ofNupharluteum.13C chemical shift data for the methyl and ring carbons demonstrate that both methyl groups are axial in 1-epi-1′-epi-thiobinupharidine and that one of two methyls is axial in 1-epi- and in 1′-epi-thiobinupharidine.

ISSN:0008-4042    

DOI:10.1139/v75-510

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Ethylene glycol di(para-chlorobenzoate) crystals are monoclinic, space groupC2/c, witha = 12.733(9),b = 9.522(8),c = 12.762(8) Å, β = 79.63(10)°, andZ = 4. The structure was solved by direct methods from 1206 independent reflections collected on a Picker diffractometer. An anisotropic refinement led to a finalRfactor of 0.033.The molecule has a crystallographic twofold axis of rotation perpendicular to the middle of the CH2—CH2bond. Unlike ethylene glycol dibenzoate which was shown to be in thetrans-conformation, this derivative is nearly in thegauche-conformation. However the same significant shortening of the ethylene part of the molecule is observed: the CH2—CH2distance is only 1.493(2) Å. The molecules are held in the crystal by van der Waals interactions only.

ISSN:0008-4042    

DOI:10.1139/v75-511

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Conformational energies were calculated for the molecule ethylene glycol diacetate, using semiempirical methods. Several conformations corresponding to thetransandgauchestates of the C—O and C—C single bonds are preferred. Theg±state of the C—O bond is shifted from ± 120° by 10 to 32°. The relative energies of the various preferred conformations are found to depend on the value of the valence angle C—O—C. Calculations with C—O—C ranging from 110 to 124° showed that a value of 115° would be preferred for this angle. The predicted values of the torsion angles and bond angles are found to be in agreement with the crystal structure data on the benzoate derivatives of ethylene glycol.

ISSN:0008-4042    

DOI:10.1139/v75-512

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A detailed description of the virtual bond method is presented. Simple equations are set up to examine the various relative dispositions of the repeating units along the polymer helix, if the repeat distance and the screw symmetry are known from X-ray data. The method is demonstrated with the examples of β-D-1,4′-xylan helix and the α-helix. Due to the rapidity and simplicity of this procedure, the effect of using different geometries for the residues can be examined readily. Diagrams are presented, from which one can deduce the torsion angles, ψ for the various values of the valence angle at the bridge atom. This method does not involve a prior knowledge ofψ and hence, derivation of atomic coordinates of the residue for Fourier transform or structure factor calculations is simple.

ISSN:0008-4042    

DOI:10.1139/v75-513

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

We have examined the effect of reducing MoS3in hydrogen in the range 450–800 °C on the properties of the resulting MoS2catalyst. The appearance of rhombohedral MoS2at 800 °C is disputed. Instead, an 'overreduced' catalyst containing some Mo metal and hexagonal MoS2was formed. Catalytic activity in thiophene hydrodesulfurization was insensitive to pretreatment.

ISSN:0008-4042    

DOI:10.1139/v75-514

出版商:NRC Research Press    

年代:1975

数据来源: NRC