Ethylenic linkages, determination

The number of ethylenic linkages In a given compound can be established with accuracy by quantitative titration with perbenzoic acid. A solution of the substance ajid excess of perbenzoic acid in chloroform is allowed to stand for several hours at a low temperature and the amount of unreacted perbenzoic acid in solution is determined a blank experiment is run simultaneously. 

These two bases have not been submitted to extensive chemical study. Ajaconine has long been known (32) to occur in Delphinium ajads L., but its empirical formula (11, 12) cannot be considered to be established with certainty. Ajaconine absorbs one molar proportion of hydrogen on hydrogenation (12), and at least one ethylenic linkage must therefore be present. Formation of a methiodide (11) establishes the presence of a tertiary nitrogen atom results of AT-methyl determinations are very low, however, and the nature of the AT-alkyl is thus uncertain. 

Paxson and Randall [38] in their method use the reference chemical shift data obtained on a predominantly isotactic polypropylene and on an ethylene-propylene copolymer (97% ethylene). They concluded that the three ethylene-propylene copolymers used in their study (97-99% propylene) contained principally isolated ethylene-ethylene linkages. Knowing the structure of their three ethylene-propylene copolymers, they used the C-NMR relative intensities to determine ethylene-propylene contents and thereby establish reference copolymers for the faster IR method involving measurements at 732 cm (13.66 pm). After a detailed analysis of resonances Paxson and Randall [38] concluded that methine resonances 4 and 5 (Table 10.1) gave the best quantitative results to determine the comonomers composition. The composition of the ethylene-propylene copolymers was determined by peak heights using the methine resonances only. In no instance was there any evidence for an inclusion of consecutive ethylene units. Thus, composition data from C-NMR could now be used to establish an IR method based on a correlation with the 732 (13.66 pm) band which is attributed to a rocking mode, r, of the methylene... 

Raman spectroscopy can differentiate between internal and external bonds as well as cis and trans isomerism and conjugation in compounds with ethylenic linkages. The type of unsaturation in butadiene and isoprene rubbers can be determined from the intense Raman scattering of the C=C stretching modes [55]. The trans- and cw-l,4-polybutadiene structures scatter at 1664 and 1650 cm , respectively. The 1,2-vinyl structure of polybutadiene scatters at 1639 cm and this scattering is well-resolved from that of the 1,4-polybutadiene structures. For poly-isoprene, a slightly different situation prevails. The cis- and ran -l,4-polyisoprene structures are riot resolved, and they scatter at 1662 cm , but the 3,4-polyisoprene structure scatters at 1641 cm , and the 1,2-vinyl stracture scatters at 1639 cm [56,57]. 

The structure of this compoimd 63a was determined by H and C NMR spectroscopy. The H NMR spectrum shows singlets at 1.45 ppm for the methyl protons, and at 4.17 and 6.30 ppm for the hydroxylic and ethylenic protons. The addition regioselectivity in the formation of 63a was established by H- C HMBC 2D-NMR, which shows the C5-C4-C3-Me linkages. The ethylenic proton correlates only with three carbon atoms Ce, C5, and C3. The methyl protons correlate with C3 and with the ethylenic carbon C4, consistent with the neighboring C3-C4 connection. The NOESY spectrum shows... 

The condensation of 2V,A -bis(3-aminopropyl)ethylenediamine (7V,A -ethylene-bis[l,3-propanediamine]) as its acid salt with 2,3-butanedione (biacetyl) in the presence of cobalt(II) or nickel(II) acetate gives complexes of 2,S-Mej [14] - 1,3-diene-l,4,8,11-N4 containing one a-diimine linkage. Experiments have shown that the presence of H ion determines whether or not a macrocyclic complex forms and that, in the presence of H, the time at which the metal acetate is added to the reaction mixture influences the yield of the complex. Unlike the reaction between biacetyl and 1,3-propanediamine to form 2,3,9,10-Me4[14]-1,3,8,10-tetraene-l,4,8,11-N4 (Sec. 4), the condensation of biacetyl withTVA -bis(3-aminopropyl)ethylenediamine is particularly sensitive to excess acetate so that the procedures given use the optimized conditions. 

Moore, C.G. Trego, B.R. Structural characterization of vulcanizates. Part IV. Use of triphenylpho-sphine and sodium di-n-butyl phosphite to determine the structures of sulfur linkages in natural rubber, cis-l,4-polyisoprene, and ethylene-propylene rubber vulcanizate networks. J. Appl. Polym. Sci. 1964, 8, 1957. 

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