Alkenes determination

Gycloisomerization of a disubstituted alkyne sometimes required activation of the alkyne by the addition of a conjugated carbonyl and performing the reaction at a higher temperature as in Equation (38). The geometry of the alkene determines the regioselectivity of the /3-hydride elimination, as ( )-60 gave predominantly 61 (Equation (38)), while 62 was the major product of the cycloisomerization of (Z)-60 (Equation (39)). 

Strain and steric properties of the alkenes determine the rate of insertion. The carbomethoxy complex (dppp)PdC(0)OCH3+ turned out to be less reactive than the corresponding acetyl-palladium (dppp)PdC(0)CH3+, which was ascribed to the higher nucleophilicity of the acetyl group as compared to the carbomethoxy group. 

Methyl substitution at the terminal carbon of the alkene determined a decreased selectivity and/or a decreased yield of the analogous products. However, the pyrroline 8 was selectively obtained from 7 the reduction with lithium aluminum hydride afforded the c -pyrrolidine 9 (X-ray)131. 

We Have seen (Secs. 5.14, 5.23) that the stability of alkenes determines orientation in dehydrohalogenation and dehydration. 

We have seen that the substituent on the alkene determines the best mechanism for chain-growth polymerization. Alkenes with substituents that can stabilize radicals readily undergo radical polymerization, alkenes with electron-donating substituents that can stabilize cations undergo cationic polymerization, and alkenes with electron-withdrawing substituents that can stabilize anions undergo anionic polymerizations. 

Bromination of alkenes is stereospecific because the geometry of the starting alkene determines which product diastereoisomer is obtained. We couldn t demonstrate this with cyclohexene because only a Z double bond is possible in a six-membered ring. But bromination or chlorination of Z and -2-butene in acetic acid produces a single diastereoisomer in each case, and they are different from each other. Anti addition occurs in both cases—more evidence that a bromonium ion is the intermediate. 

R2C CHR - R2CO + R CHO These could be identified, and the structure of the original alkene determined. 

Os-2-alkenes react a few times faster than tra 5-2-alkenes. Steric influences, both from the complex part and the alkene, play a dominant role in determining the fate of hydroformylation of alkenes not containing functional groups. For alkenes such as styrene, 3,3,3-trifluoropropene, acrylates, and vinyl esters, the electronic properties of the alkene determine to a large extent the regioselectivity. 

Anti addition across r-2-butene leads to a pair of enantiomers, while anti addition across trans-2-butene leads to a meso compound. These examples illustrate that the configuration of the starting alkene determines the configuration of the product for halogenation reactions. 

Hardas, N.R. Adam, R. Uden, P.C., Alkene Determination by Bromination and Gas Chromatography with Element-selective Atomic Plasma Spectroscopic Detection, J. Chromatogr. A, 1999, 844, 249-258. 

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