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Double bonds moving

The situation with benzene is similar to that with acetate. The tt electrons in the double bonds move, as shown with curved arrows, but the carbon and hydrogen atoms remain in place. [Pg.45]

Olefin Isomerization. One other type of hydrocarbon isomerization is on the threshold of commercialization—namely, that of olefins. Processes for olefin isomerization were first developed some 15 years ago (11, 14, 20) after it was recognized that highly branched olefins have higher octane numbers than do their straight-chain isomers, and that the octane numbers of olefins increase as the double bond moves toward the middle of the molecule. [Pg.120]

Now the leaving group can be expelled by the enol the double bond moves back into its original position in this step, which is exactly the same as the final step of an ElcB reaction (Chapter 19). The new1 double bond expulsion oj the leaving group from the enol intermediate... [Pg.586]

Cyclization with acid now causes a lot to happen. The 1,4-dicarbonyl compound cyclizes to a lactone, not to a furan, and the redundant ester group is lost by hydrolysis and decarboxylation. Notice that the double bond moves into conjugation with the lactone carbonyl group. Finally, the reduction gives the furan. No special precautions are necessary—as soon as the ester is partly reduced, it loses water to give the furan whose aromaticity prevents further reduction even with UA1H4. H... [Pg.1189]

This intermediate cannot cyclize as it has a tram double bond and the ends cannot reach each other. First, the double bond is moved out of conjugation with the COSR group, again as in the fatty acids, except that here the new Z double bond moves into conjugation with the remaining keto... [Pg.1435]

IR absorptions due to double bond stretching motions (1663 cm and 1655 cm ) change on dimerization. In the dimer, absorption for an isolated double bond appears, and that for a conjugated double bond moves to longer wavelengths. [Pg.138]

The situatiOD with benzene is similar to that w ith nitmmethane The TT eloctrooa in the double bonds move shown wiUi curved arrows, bwi the carbon and hydrogen atomw remain In place. [Pg.66]

The second reaction starts with nucleophilic attack by the amine on the more electrophilic carbonyl group - the ketone. Imine formation is followed by cyclization and this second step is i normal nucleophilic substitution at the carbonyl group of an ester (Chapter 12). The imine double bond moves into the ring to secure conjugation with the ester. [Pg.106]

As we saw in Part III of A Preview of Carbonyl Compounds, the most gejb eral reaction of aldehydes and ketones is the nucleophilic addition reaction. A nucleophile, Nu , attacks the electrophilic C=0 carbon atom from a direction approximately 45 to the plane of the carbonyl group. At the same time, rehybridization of the carbonyl carbon from sp to sp occurs, an electron pair from the carbon-oxygen double bond moves toward the electronegative oxygen atom, and a tetrahedral alkoxide ion intermediate is produced (Figure 19.1). [Pg.760]

Substituents which start at the end of the double bond should finish next to the ring the formation of 45 is a particularly impressive example as the double bond moves out of conjugation. These are the most tricky type of Claisen rearrangement and other products can be formed if conditions are not carefully controlled.9... [Pg.95]

Corey s method20 relies on metal exchange with the bromocyclopropane 69 prepared by carbene addition. The extra stabilisation of cyclopropyl anions (chapter 8) makes both this lithium derivative and the ylid 63 more easily handled. Addition to aldehydes or ketones gives mixtures of adducts 70 [it turns out that none of the stereochemistry of 69 or 70 matters] which fragment under Lewis acid catalysis to give the thioacetal 71. Careful hydrolysis releases the 3,4-enal -72, the product of a homoaldol reaction with an aldehyde homoenolate and RCHO and a difficult compound to make as the double bond moves into conjugation very easily. [Pg.194]

Whenever it is possible to draw two or more Lewis structures for a species that differ only in the location of a double bond between the same two kinds of atoms (N and O in this case), the true structure of the species is the average of the individual structures. In a sense, two of the four electrons in the double bond move from one N-O bond to the next so quickly that each bond is more than a single but not quite a double bond. That pair of electrons is not localized between two atoms rather it is delocalized over the entire species. Delocalization gives rise to a condition known as resonance, which adds stability to the species. One way delocalization can be shown in a Lewis structure is to use dotted lines to represent the pair of delocalized electrons, as shown in the following figure. This figure is a composite of the three resonance forms of the nitrate ion. [Pg.276]

The substituent X moves two atoms along the chain, and the double bond moves in the opposite direction to the position where X is still an allylic group. This migration can occur so readily that it is reasonable to regard the isomerization of allyl halides as true tautomerism. For example, equilibrium between 2-butenyl bromide and 1-methylallyl bromide is set up in a few hours at 75° 14... [Pg.1056]


See other pages where Double bonds moving is mentioned: [Pg.163]    [Pg.15]    [Pg.247]    [Pg.248]    [Pg.153]    [Pg.620]    [Pg.520]    [Pg.159]    [Pg.1216]    [Pg.25]    [Pg.237]    [Pg.281]    [Pg.23]    [Pg.72]    [Pg.124]    [Pg.68]    [Pg.124]    [Pg.25]    [Pg.156]    [Pg.281]    [Pg.1037]    [Pg.117]    [Pg.224]   
See also in sourсe #XX -- [ Pg.539 ]




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