摘要:

Ether-type linkages are formed as by-products during the preparation of polyethylene terephthalate from dimethyl terephthalate and ethylene glycol. Incorporated in the polymer, these linkages affect its physical and mechanical properties such as tensile strength, melting point, and resistance to oxidation. An improved chemical method of analysis has been developed allowing an accurate determination of ether bonds in polyester fibres. The method is based on the selective oxidation of ethylene glycol with periodic acid and takes advantage of hydrolysis with water under pressure to decompose the polymer. The method has been employed to study the effect of the concentration of polycondensation catalyst on the formation of ethers.

ISSN:0008-4042    

DOI:10.1139/v78-445

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The apparent molal volumesand beat capacitiesof oligopeptides of glycine, alanine, and serine have been determined in water at 25 °C by flow densimetry and flow microcalorimetry. The data are reported for the homologous series: glycine to pentaglycine,L-alanine to tetra-L-alanine andL-serine to tri-L-serine. From the limitingandvalues of the glycine oligomers, the contributions of the glycyl residue in an extended polypeptide chain has been evaluated as:andThe data for the other peptides are discussed in terms of contributions from the amino acid side chains, i.e. —CH3and —CH2OH, and end-group hydration effects. Some necessary conditions for obtaining useful additivity schemes for predictingandof extended polypeptides and proteins are indicated.

ISSN:0008-4042    

DOI:10.1139/v78-446

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The photoelectron spectra of stilbene and 4-R-stilbene (R = CH3O, CH3, F, Cl, NO2) has been determined and the five highest Π ionization potentials assigned. By considering the stilbenes to be formally constituted by union of a styrene and substituted benzene the influence of substituent on molecular orbital energies gas been rationalized. The data suggest that the stilbenes exist in a planar or nearly planar configuration in the gas phase. CNDO/2 calculations have been performed on a wider variety of 4-R-stilbenes (R = NH2, CH3, OH, F, CN, CF3, NO2) and it is suggested that planar configurations also predominate for those stilbenes. First ionization potentials of some of the stilbenes are correlated with bromination and ozonolysis rate data.

ISSN:0008-4042    

DOI:10.1139/v78-447

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The synthesis of the β-lactam19from anthranilic acid is described.

ISSN:0008-4042    

DOI:10.1139/v78-448

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The synthesis of the β-lactam34from 3-methoxy-2-nitrobenzaldehyde is described.

ISSN:0008-4042    

DOI:10.1139/v78-449

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The reaction of alkali metals with tertiary alkyl nitriles eventually gives, after protonation, an imine. α-tert-Alkylketones are produced by the hydrolysis of these imines. This reaction, involving radical anion intermediates, is a simple method for the synthesis of highly hindered symmetric ketones.

ISSN:0008-4042    

DOI:10.1139/v78-450

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

In nmr spectroscopy involving organic substrates, one often has a situation in which there is a dominant species in rapid equilibrium with one or more minor components. In general, one knows, a priori, neither the population of these minor components nor the rate constants involved in the equilibrium process. In fact, from the physical appearance of these spectra, one cannot normally even deduce that such an equilibrium exists. For example, in cases involving13C nmr spectroscopy, this minor component may not be observable under slow exchange nmr conditions because of signal-to-noise ratio problems and hence is referred to as a 'hidden' exchange partner. In this paper, we have analyzed the extent of nmr line broadening to be expected from a two-component system of this type, varying the populations, chemical shift separations, and intrinsic line widths. Thus, the presence of a 'hidden' partner can sometimes be detected by a characteristic, but often very subtle, peak broadening–resharpening sequence involving first of all the 'averaged' peak and finally the peak of the dominant component, these peaks being virtually identical in area and very similar in chemical shift so that one is not easily alerted. Assuming there is some experimental line broadening, equations developed in this paper, together with chemical shift estimates for this 'hidden' partner, allow one to quickly estimate both the amount of the minor partner and the rate constant involved. Three 'real life' situations are subsequently analyzed.

ISSN:0008-4042    

DOI:10.1139/v78-451

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

N,N′-Dibenzoyl-2,5-dideoxystreptamine (8b) reacted with thionyl chloride to form the bisoxazoline9and the latter compound was treated with thiobenzoic acid to produce the dithiobenzoate10a. Removal of the protective groups in10aafforded (l,3/4,6)-4,6-diamino-1,3-cyclohexanedithiol (1) dihydrochloride. Reaction of8bwith triethyl orthoacetate in the presence of boron trifluoride yielded the monooxazoline12which, on reaction with thiobenzoic acid followed by deprotection of the resulting13a, afforded (d,l)-(13/4,6)-4,6-diamino-3-hydroxycyclohexanethiol (2) dihydrochloride. Similarly, 3-N-benzoyl-1-N-ethoxycarbonyl-2,5-dideoxystreptamine (15) and l-N-benzoyl-3-N-ethoxycarbonyl-2,5-dideoxystreptamine (20) were converted via their respective oxazolines17aand22a, to the enantiomeric aminothiols3and4. Protected derivatives of1–4are also described.

ISSN:0008-4042    

DOI:10.1139/v78-452

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Field desorption mass spectra are reported for a series of sodium carboxylates. Above 20 mA the major ions in the spectra belong to the series [xNa+ + (x − 1)RCOO−]+with values ofxnormally extending throughout the measurable mass range. Desorption characteristics and spectral composition have been shown to be strongly modified by the addition of fructose and other polyhydroxy compounds. Thus, the sodium acetate spectrum is more intense and contains higher aggregates when 0.1–0.2 mol of fructose is added. With further additions the ionized free acid, AcOH+•, becomes the base peak in a low intensity spectrum recorded at 17–18 mA. The main ion from fructose is the sodium complex which does not exceed 20% of the base peak. Added fructose also has a beneficial effect on sodium 12-hydroxystearate but the improvement is less dramatic and there are some complications in the interpretation. A sample of technical lithium stearate contains the usual complexes up to [Li4(RCOO)3]+and the presence of important amounts of palmitate gives rise to all possible combinations of the two carboxylate anions in these complexes. Smaller amounts of Li2Na, Li3Na, and Li3K complexed with the appropriate number of anions give evidence of alkali metal impurity.

ISSN:0008-4042    

DOI:10.1139/v78-453

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The behaviour of 1,1-diphenyl-2-(2-thienyl)ethylene towards electrophilic agents (Br2, HNO3) has been investigated and the structure of reaction products assigned by uv,1H nmr spectra, and dipole moment measurements.

ISSN:0008-4042    

DOI:10.1139/v78-454

出版商:NRC Research Press    

年代:1978

数据来源: NRC