摘要:

Wide line nmr and differential scanning calorimetric studies confirm the existence of crystal phase transitions in piperidinium iodide. The highest temperature phase involves isotropic rotation of the piperidinium ion. No crystal structure transitions occur in the chloride, bromide, or hexafluorophosphate salts although these compounds undergo second moment transitions indicating probable rotation of the piperidinium ion about the N—C3axis.

ISSN:0008-4042    

DOI:10.1139/v76-500

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Standard enthalpies of solutions of sodium bromide, potassium bromide, tetrabutyl phosphonium bromide, tetraphenyl phosphonium bromide, and sodium tetraphenyl boron have been measured in 20%, 44.5%, and 64.5% dioxane–water mixture. On the extra thermodynamic assumption ΔΔHs(Ph4P+) = ΔΔHs(−BPh4) single ion enthalpies of transfer from water to dioxane–water mixtures have been calculated for various ions.

ISSN:0008-4042    

DOI:10.1139/v76-501

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A series of lithium, sodium, potassium, and ammonium salts were investigated by proton magnetic resonance spectroscopy in 1,3-dimethylethyleneurea, a relatively new non-aqueous solvent of high polarity and moderately high dielectric constant. The salts were found to shift the solvent proton peaks linearly as a function of salt concentration. Thiosulfate, perchlorate, and iodide salts shifted the solvent peaks downfield while tetraphenylborate salts uniquely shifted the peaks upfield indicating an unusual type of solvation behavior for the tetraphenylborates in this solvent.

ISSN:0008-4042    

DOI:10.1139/v76-502

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Considerable variation in the measurement of polymer–solvent interactions using gc retention data may occur due to kinetic factors, surface excess concentrations of probe vapour, and non-linear partition isotherms. The kinetic factors, which appear as a flow rate dependence of the retention volume, are analysed in terms of a previously reported theoretical model for retention on polymeric stationary phases passing through the glass transition. The predicted linear extrapolations to zero flow rate are obtained for the retention ofn-tetradecane on polystyrene. The variation of this flow rate dependence with temperature and with the thickness of the stationary phase are also in qualitative agreement with the theory. A simplified model for the effect of loading on the retention diagram is presented. Non-linear absorption and bulk sorption isotherms result in a dependence of retention volume on sample size, necessitating an extrapolation of the measured retention volumes to zero peak height. The temperature variation of the flow rate dependence, the effect of loading, and the effect of sample size on retention volume are all further complicated by uneven distribution of polymer on support. From scanning electron micrographs of the beads it is evident that 'beading up' of the polystyrene on the glass surface may occur at low loadings, resulting in a non-uniform coating with large areas of the beads uncoated. It is concluded that in order to obtain reliable data on polymer–solvent interactions using gas chromatography, all of the above-mentioned factors must be considered.

ISSN:0008-4042    

DOI:10.1139/v76-503

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Reaction of 2,4-cholestadiene, 2,4-androstadien-17-one, or 3-trimethylsiloxy-2,4-cholestadiene with dimethyl acetylenedicarboxylate or methyl propiolate in boiling xylene results in the cleavage of rings A and B and the formation of 4-(2-arylethyl)-5-isopropenyl-7a-methyltetrahydroindane derivatives. They are considered to be formed via Diels–Alder addition of the acetylene to the steroid diene followed by a retro-Diels–Alder cleavage of the resulting bicyclo[2.2.2]octadiene system. Attempts to isolate the Diels–Alder adducts by carrying out the additions at lower temperature were unsuccessful, since no reaction occurred. However, when 2,4-androstadien-17-one was treated with dicyanoacetylene in boiling benzene, it was possible to isolate a mixture of two stereoisomeric Diels–Alder adducts containing the bicyclo[2.2.2]octadiene system in ring A; this was converted in boiling xylene to a retro-Diels–Alder product analogous to the products obtained with the other acetylenic dienophiles.

ISSN:0008-4042    

DOI:10.1139/v76-504

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The acyclic amido radicals generated from the correspondingN-bromo-N-tert-alkylamides reacted likeN-radicals, rather thanO-radicals, and preferentially abstracted a δ-hydrogen of the alkyl chain, rather than a γ-hydrogen of the acyl chain. On the basis that, in these amido radicals, the conformation of the transition state of the hydrogen transfer is a five-membered ring and the stereoelectronic requirement for the transfer demands a colinear arrangement of the radical containing orbital and the C—H bond, the results are satisfactorily rationalized by the II electron configuration of the amido radicals. It is also established that the chain length of theseN-bromoamide photodecompositions increases as the intramolecular hydrogen transfer of the corresponding amido radicals becomes easier; the hydrogen abstraction step must be the rate determining step in the chain reaction. The spontaneous formations of γ-iminolactones from γ-bromoamides indicate that the intramolecular nucleophilic displacement by theO-center of the amido group is facilitated since its transition state conformation readily accommodates the stereoelectronic requirements for the nucleophilic substitution. A colinear approach of thep-orbital of the more nucleophilicN-center to the rear side of the γ-C—Br bond is shown to be prohibitively strained.

ISSN:0008-4042    

DOI:10.1139/v76-505

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A simple, selective pulse sequence has been developed whereby the equivalent of a continuous wave INDOR nmr experiment, can be performed in the pulse Fourier transform mode of operation. The advantages and limitations of this approach for proton nmr studies are demonstrated with four samples, uridine (1), cytidine (2), vinyl acetate (3), and 2,3,4,-tri-O-acetyl-1,6-anhydro-β-D-mannopyranose (4). The observed responses depend upon the flip angle of the monitoring pulse. A small flip angle (20–30°) detects responses only for those transitions having an energy level in common with the perturbed transition, whereas a 90°-flip angle also results in responses from those transitions which have an indirect connectivity relationship.

ISSN:0008-4042    

DOI:10.1139/v76-506

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

4-(1-Hydroxyethyl)-3,3,5,5-tetramethylcyclohexanone has been prepared to serve as a model for 3,3,5,5-tetramethylcyclohexanone on which the reduction stereochemical product ratio may be experimentally determined. Reduction with sodium borohydride in 2-propanol gives two epimers in a 95.5:4.5 ratio. The major isomer is shown to be the less stable by equilibration over Raney nickel. Proton and13C nmr spectra confirm that this major epimer iscis-4-(1-hydroxyethyl)-3,3,5,5-tetramethylcyclohexanol and show that this compound exists predominantly in the conformation with an axial hydroxyethyl group and an equatorial hydroxyl group. It is concluded that reduction of this model compound proceeds at least 95.5% by equatorial attack.

ISSN:0008-4042    

DOI:10.1139/v76-507

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Bromine intercalates can be used as electrodes in concentration cells. Voltages of the order of 50 mV can be obtained with thermal gradients of 60–75 °C, in the range 0–100 °C. The cell can be operated on a continuous basis by allowing the high activity electrode to distill bromine to the low activity electrode.

ISSN:0008-4042    

DOI:10.1139/v76-508

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

This paper describes the synthesis of1, a spin-labeled analog ofN,N-dimethyl-2-phenyl-aziridinium chloride2. The compound is formedin situfrom3band acts as a poor competitive inhibitor of bovine erythrocyte acetylcholinesterase with aKivalue ofM.

ISSN:0008-4042    

DOI:10.1139/v76-509

出版商:NRC Research Press    

年代:1976

数据来源: NRC