Double-bond sequence

In a recent report, Shi et al. developed a valuable tool for the synthesis of 2,6-trans substituted morpholines by addition of water and alcohol to epoxy alkynes [109]. The procedure involved a domino three-membered ring opening, 6-exo-cycloisomerization, and subsequent intra-or intermolecular nucleophilic addition or a double-bond sequence. 

Allenes are compounds that also exhibit stereoisomerism. Allenes are molecules that contain the following double-bond sequence ... 

To conclude this section, an example is given of the application of statistical models to examine double bond sequences in polymers with unsaturated backbones. The presence of backbone unsaturation leads to the occurrence of cisitrans isomerism and this can be treated entirely analogously to comonomer sequence. Ivin [42] and others have used NMR spectroscopy extensively to study the microstructure of polymers prepared by transition metal catalysed ring-opening metathesis polymerisation (ROMP) such as polynorbornene (PNB). 

PVC is a special case because it rapidly loses hydrogen chloride on heating, leaving unsaturated carbon-carbon double bond sequences (polyenes) that are sites of instability. As a result PVC always needs a heat stabiliser. 

Figure 31 Various double-bond sequences of substituted polybutadiene.

The first two reactions yield unsaturated polymeric products that are more or less colored, depending on the extent of reaction. The color of the degraded macromolecular compounds is related to the length of the resulting conjugated double bond sequences. 

To prevent or to limit the formation of conjugated double bond sequences by promoting addition reactions or by functioning, as an oxidation catalyst to stabilize the color of PVC. 

Conjugated linoleic acid (CLA) is the collective name given to a group of Cj positional and geometric isomers containing two conjugated double bonds, rather than the more common methylene-interrupted double bond sequence. An example of one such isomer is shown in Figure 1. 

The method was applied to the synthesis of (-t-)-l9-nortestosterone by the following sequence of reactions. Michael addition of the bisannulation reagent 124 to the optically active keto ester 129 and decarboxylation afforded 130, and subsequent aldol condensation gave 131. Selective Pd-catalyzed oxidation of the terminal double bond afforded the diketone 132 in 78% yield. Reduction of the double bond and aldol condensation gave ( + )-19-nortestosterone (133)[114]. 

The longest continuous chain that includes the double bond forms the base name of the alkene and the chain is numbered in the direction that gives the doubly bonded carbons their lower numbers The locant (or numerical position) of only one of the dou bly bonded carbons is specified in the name it is understood that the other doubly bonded carbon must follow in sequence... 

No locants are needed m the absence of substituents it is understood that the double bond connects C 1 and C 2 Substituted cycloalkenes are numbered beginning with the double bond proceeding through it and continuing m sequence around the ring The direction is chosen so as to give the lower of two possible numbers to the substituent... 

Unsaturated branched acyclic hydrocarbons are named as derivatives of the chain that contains the maximum number of double and/or triple bonds. When a choice exists, priority goes in sequence to (1) the chain with the greatest number of carbon atoms and (2) the chain containing the maximum number of double bonds. 

This tendency is related to the polarization properties of the monomer substituents (42). Monomers that are dissimilar in polarity tend to form alternating monomer sequences in the polymer chain. An example is the monomer pair acrylonitrile—styrene. Styrene, with its pendent phenyl group, has a relatively electronegative double bond whereas acrylonitrile, with its electron-withdrawing nitrile group, tends to be electropositive. 

The dimsyl ion also adds to carbon—carbon double bonds, and if the mixture is heated for several hours, methanesulfenate is eliminated. The overall result is methylation, and for compounds such as quinoline or isoquinoline (eq. 20), yields ate neady quantitative (50). The reaction sequence for isoquinoline to 1-methyhsoquinoline is as follows ... 

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