Linkages isolated ethylenic

All compounds with an isolated ethylenic linkage exhibit an intense absorption band (e 10,000) around 190 mp due to the n -> tt transition4. For all practical purposes, an isolated ethylenic linkage need not be considered a chromophore , since it gives rise to a band in the not easily accessible far ultra-violet region. ... 

It was mentioned in the preceding chapter that an isolated ethylenic linkage gives a high intensity (e 10,000) band near 190 m/x and that an... 

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... 

Another method for the hydroxylation of the ethylenic linkage consists in treatment of the alkmie with osmium tetroxide in an inert solvent (ether or dioxan) at room temperature for several days an osmic ester is formed which either precipitates from the reaction mixture or may be isolated by evaporation of the solvent. Hydrolysis of the osmic ester in a reducing medium (in the presence of alkaline formaldehyde or of aqueous-alcoholic sodium sulphite) gives the 1 2-glycol and osmium. The glycol has the cis structure it is probably derlv from the cyclic osmic ester ... 

The addition of an alkyl radical to an ethylenic linkage, as demonstrated by the conversion of 45 to 46, can be explained in terms of at least two mechanisms. The first is that carbonyl activation is a prerequisite for the initial attack of the alkyl radical upon the double bond, which implies that the addition is closely related to the Michael reaction.9 If this view is correct, then an isolated double bond will be inert to an initial radical addition of the type 57 — 58. Alternatively, one can argue that any suitably placed double bond, isolated or otherwise, can be attacked by an alkyl radical in these terms the ultimate product formed depends on the energy of the intermediate radical. 

Since deacetylation of LXXXII and subsequent ozonization and treatment with water afforded glyoxal (isolated as the phenylosazone) it followed that the ethylenic linkage must be between carbon atoms 2 and 3.204 Reduction of LXXXII, followed by deacetylation, yields ethyl 2,3-didesoxy-D-alloside (LXXXIII). Alternatively, LXXXI could be converted into 4,6-diacetyl-2,3-didesoxy-D-allose, which on glycosidation as above yielded ethyl 4,6-diacetyl-2,3-didesoxy-D-alloside. In this instance the product was a mixture of isomers, since on deacetylation, two forms (m. p. 72-72.5° and 90°, respectively) were isolated. Derivatives of 2,3-didesoxy-L-ribose81 have been prepared from 3,4-diacetyl-L-arabinal,... 

The synthesis of (84) is effected by heating glycine in solvent such as ethylene glycol (Expt 8.38). Brief treatment with hot concentrated aqueous hydrochloric acid cleaves one of the amide linkages with the formation of the dipeptide, glycylglycine, which is isolated as the hydrochloride monohydrate and may be converted into the ester hydrochloride under Fischer-Speier conditions (Section 5.12.3, p. 696). 

The action of ozone on acetylene is very violent and explosions result when the reaction is conducted in the vapor phase. However, it is possible to study the mechanism of the reaction by carrying out the ozonization in solution. The ozonide formed in this way is too unstable to be isolated and only by allowing a very slow decomposition to occur by slow evaporation of the solvent is it possible to isolate reaction products. In this way, it has been found that the material remaining after evaporation of the solvent consists of a large proportion of glyoxal (SI per cent) and a small amount of formic acid (5.6 per cent).1,12 The decomposition of the ozonide of acetylene differs from that of ethylene in that the linkage of carbon to carbon is not destroyed. The direct oxidation of acetylene with ozone, however, results in die formation oi formic acid and carbon dioxide.188... 

A second alkaloid from Streptomyces sp. NA-337, CioHnNO, proved to be a tertiary base (not N-methyl), reducible by borohydride to a secondary amine and therefore containing a C=N group. N.m.r. spectral study revealed an ethylidene group (5 2.18d and 6.32q, J = 8 Hz) and a cis ethylenic linkage (8 6.94d and 8.44d, 7 = 6 Hz). The oxygen atom was suspected of being ethereal since the i.r. spectrum showed neither OH nor C=0 bands. Structure (20), which was proposed on spectral and chemical evidence, is the same as that advanced earlier for a base isolated from Streptomyces abikoensis and called abikoviromycin. The identity of the two was settled beyond doubt by a direct comparison between the methiodide of the N-methyldihydro-base and 4,4a-epoxy-5-( )-ethylidene-l-methyl-2,3,4,4a,5,7a-hexahydro-lH-l-pyrindine methiodide (21), derived from abikoviromycin. ... 

Introduction of an ethylenic linkage by removal of two halogen atoms from a vicinal dihalide has little synthetic importance since the requisite dihalides are almost always obtained by addition of halogen to the double bond that is to be formed. However, the process is valuable because the halogen adducts can be useful for isolation or separation of a product. 

Isolated from wool-fat. Needles from EtOH. M.p. 162. [a]i + 70-4 in CHCI3. Contains 3 ethylenic linkages. Probably a triterpene Acetyl needles from AoOEt. M.p. 173- 4 . [a] + 0O-3 in CHCL. 

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