Alkene homologation

We deduced from equations 4 and 7 that only when the slope, m, is approximately equal to 1 will the enthalpies of hydrogenation for a homologous series of alkenes be reasonably constant. Inspecting the slope and intercept data from equation 7 in Table 2, together with the actual experimental enthalpies of hydrogenation, shows our conclusion to be valid. We define for each alkene homologous series... 

Comparing the effect of the double-bond migration within the identical cr-frameworks of isomeric isoalkyl-1-alkenes and the 2-methyl-1-alkenes, we find that the individual enthalpies of isomerization for Cg-Cs are —10.4, —10.9 and —11.3 kJmol-1. These mono- to disubstituted isomerization enthalpies are very similar to those for isomerization of the 1-n-alkenes to the tram -2-n-alkenes, homologous series which also possess a common structural skeleton. 

Table 6.2.2 The first four members oj the alkene homologous series (C H2 )...

Hydrocarbons like ethene, H2C=CH2, that possess one carbon-to-carbon double bond (C=C), belong to the ALKENE homologous series. The suffix -ene indicates the presence of the C=C bond. Since the alkenes have two fewer H atoms than the corresponding alkanes, their general formula is C H2 , where n is a whole number larger than 1. 

Diacetylene and its homologs react with alkene- and arenecarbonitrile iV-oxides (25-30°C, EtaO, 3 h) (59G598 66ZOR615). The reaction proceeds stepwise to... 

Alkenes also form a homologous series as the carbon number increases, the number of possible isomeric structures for each member increases more rapidly than in the case of the alkane series. 

The Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

Asymmetric tandem cycloaddition of a chiral carbohydrate nitroalkene with ethyl vinyl ether in the presence of electron-withdrawing alkenes produces a facile assembly of bicyclic systems, which can further be selectively cleaved to give homologated carbohydrates (Eq. 8.110).176... 

Many Pseudomonas strains accumulate MCL-PHAs from alkane, alkene, al-kanoate, alkenoate, or alkanol [5,6,14,96]. The composition of the PHAs formed by the pseudomonads of the rRNA homology group I is directly related to the structure of the carbon substrate used [6]. These results suggested that MCL-PHAs are synthesized from the intermediates of the fatty acid oxidation pathway. In almost all pseudomonads belonging to the rRNA homology group I except Pseudomonas oleovorans, MCL-PHA can also be synthesized from acetyl-CoA through de novo fatty acid synthetic pathway [97]. The -oxidation pathway and de novo fatty acid synthetic pathway function independently in PHA biosynthesis. 

Alkylated diphosphines (R,R)-(92) and (93) were used as chiral ligands in the Pt-catalyzed hydroformylations of some alkeneic substrates. These ligands bring about a loss of catalytic activity with respect to the corresponding diphenylphosphine homolog, particularly in the case of the platinum systems. The regioselectivity favors the straight-chain (or less branched) isomer in the case of terminal alkenes with the exception of styrene the enantioselectivity is very low in all cases.320... 

Benzotriazol-l-yl)methyl]triphenylphosphonium chloride 848 reacts with BunLi and aldehydes to give l-(alken-l-yl)benzotriazoles 849. Addition of bromine to the double bond of derivatives 849 followed by a reaction with amines furnishes amides 850. A variety of primary or secondary amines can be used. This way aldehydes are conveniently homologated and converted to amides with a one-atom longer chain (Scheme 136) <2004ARK(ix)44. 

The alkenes make up a homologous series of hydrocarbons with the general formula C H2 . Alkenes show two types of structural isomerism, position isomerism and chain isomerism. Geometrical isomerism also exists because of the lack of free rotation about the C=C double bond. 

If a sample contains one or more members of a homologous series, identifications can be made using a plot of log tR against the number of carbon atoms, previously prepared from standards. The plot, which is valid for one temperature only, is linear and can be used for alkanes, alkenes, alcohols, aldehydes, ketones, esters and ethers. 

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