Ethers shifts

The distribution of ethers shifts towards more substituted species at constant temperature (80 °C) with the initial isobutene to glycerol ratio (Fig. 10.5). Changing the initial isobutene to glycerol ratio does not affect the by-product (Cg, C12 and Ci6 hydrocarbons) distribution. Temperature, however, has a clear effect on the hydrocarbon distribution the higher the temperature the smaller the fraction of C12 and CK, hydrocarbons of the total amount of hydrocarbons [8]. 

Physical properties of perfluoroethylene glycol ethers, 9F NMR signals of perfluoroethylene glycol ethers shift in ppm vs. CFCI3 external ... 

The preparation involves an oxymercuration (Section 3.5.3) of the C=C double bond of the ethyl vinyl ether. The Hg(OAc) ion is the electrophile as expected, but it forms an open-chain cation A as an intermediate rather than a cyclic mercurinium ion. The open-chain cation A is more stable than the mercurinium ion because it can be stabilized by way of oxocarbe-nium ion resonance. Next, cation A reacts with the allyl alcohol, and a protonated mixed acetal B is formed. Compound B eliminates EtOH and Hg(OAc) in an El process, and the desired enol ether D results. The enol ether D is in equilibrium with the substrate alcohol and ethyl vinyl ether. The equilibrium constant is about 1. However, the use of a large excess of the ethyl vinyl ether shifts the equilibrium to the side of the enol ether D so that the latter can be isolated in high yield. 

A water-soluble sulfonated crown ether (see Figure 80) has been prepared and used as an ion size selection reagent. In the synergistic extraction of alkaline earth ions with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone and trioctylphosphine oxide in cyclohexane, addition of the sulfonated crown ether shifted the extraction for the larger ions to a higher pH level, thereby improving the... 

The dye 4-aminophthalimide, 45, is extremely sensitive to solvent polarity because of the charge-transfer nature of its lowest singlet-excited state. The fluorescence, which peaked at 425 nm in ethyl ether, shifted to 540 nm in H2O. Correspondingly, the fluorescence quantum yield decreased from 0.53 (ether) to 0.01 (H2O). Hydrogen bonding with the solvent also contributed to observed variations of the photophysical properties of 45. Addition of a-and P-CD caused a blue shift of the fluorescence maximum to 523 nm in 10 M a-CD and to 513 nm in 10 M P-CD, an enhancement of Of (1.2 and 4 times), and an increase of the fluorescence lifetime from 1 ns to 8 and... 

We view water as consisting of two components one, ice-like with a relatively smaller compressibility, and a second, close-packed with a relatively larger compressibility. We also assume that adding ether to pure water causes a shift in the equilibrium concentration of the two components in favor of the ice-like component, giving rise to a net decrease in the compressibility of the system. This is the qualitative explanation of the observed phenomena. As we shall later see, this explanation is not entirely correct. Also, we have assumed that adding ether shifts the concentration of the two components in favor of the ice-like one. This in itself is an interesting phenomenon that, though correct, needs further explanation. We shall return to discuss this phenomenon in Chapter 3. 

Similarly, a palladium catalyzed allyl—vinyl ether shift reaction has been applied to a prostaglandin synthesis [51,55]. 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives an acetal and vinyl ether[106,107], The reaction of alkenes with alcohols mediated by PdCl2 affords acetals 64 as major products and vinyl ethers 65 as minor products. No deuterium incorporation was observed in the acetal formed from ethylene and MeOD, indicating that hydride shift takes place and the acetal is not formed by the addition of methanol to methyl vinyl etherjlOS], The reaction can be carried out catalytically using CuClj under oxygen[28]. 

H NMR The chemical shift of the proton m the H—C—O—C unit of an ether is very similar to that of the proton m the H—C—OH unit of an alcohol A range of 8 3 2-4 0 IS typical The proton m the H—C—S—C unit of a sulfide appears at higher field than the corresponding proton of an ether because sulfur is less electronegative than oxygen... 

Section 16 18 An H—C—O—C structural unit m an ether resembles an H—C—O—H unit of an alcohol with respect to the C—O stretching frequency m its infrared spectrum and the H—C chemical shift m its H NMR spectrum Because sulfur is less electronegative than oxygen the H and chemical shifts of H—C—S—C units appear at higher field than those of H—C—O—C... 

The ether oxygen of tetrahydropyran (45 X = O) induces a large downfield shift of the a carbons, while the /3 and y carbons move slightly upfield, the y more noticeably. 

In the chemical shift range for alkenes and aromatic and heteroaromatic compounds enol ether fragments (furan, pyrone, isoflavone, 195-200 Hz) ... 

The keto-carbonyl C signal at 5c = 200.9 would only fit the aflatoxins B, and M,. In the C NMR spectrum an enol ether-C// fragment can also be recognised from the chemical shift value of 5c = 145.8 and the typical one-bond coupling constant Jch = 196 Hz the proton involved appears at Sh = 72, as the CH COSY plot shows. The H triplet which belongs to it overlaps with a sing-... 

The order of enolate reactivity also depends on the metal cation which is present. The general order is BrMg < Li < Na < K. This order, too, is in the order of greater dissociation of the enolate-cation ion pairs and ion aggregates. Carbon-13 chemical shift data provide an indication of electron density at the nucleophilic caibon in enolates. These shifts have been found to be both cation-dependent and solvent-dependent. Apparent electron density increases in the order > Na > Li and THF/HMPA > DME > THF >ether. There is a good correlation with observed reactivity under the corresponding conditions. 

Another route to 5a compounds (57) proceeds from the dienol ether (58) by selective catalytic hydrogenation of the A -double bond with concomitant shift of the 3,4-double bond to the 2,3-position. If the hydrogenation is carried out in the presence of traces of base, double bond migration is suppressed and the difficultly accessible A -enol ethers of 5a-series (59) are thus obtained. 

Treatment of dibromocarbene adduct (43) (Rji, = O) with aqueous methanol containing silver nitrate or perchlorate gives A-homo-estra-1 (10), 2,4a-triene-4,17-dione (45) in 21 % overall yield from the enol ether (42). The exact pathway is not known, but the first step may be formation of a bromo-homo-dienone facilitated by the methoxyl group, which then undergoes further loss of hydrogen bromide involving shift of a double bond by enolization. ... 

Isomerization of fluoroolefins by a shift of a double bond is catalyzed by halide 10ns [7] The presence of crown ether makes this reaction more efficient [74] Prolonged reaction time favors the rearranged product with an internal double bond (equations 3-5) Isomerization of perfluoro-l-pentene with cesium fluoride yields perfluoro-2-pentenes in a Z ratio of 1 6 [75] Antimony pentafluoride also causes isomenzation of olefins leading to more substituted products [76]... 

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