Alkene Homologation, branching

There are four pairs of 1- and 2-alkenes with branching in a substituent group for which we can examine double bond migration enthalpies49 4-methyl-l- and 4-methyl-2-pentene 5-methyl-1- and 5-methy 1-2-pentene 4-methyl-l- and 4-methyl-2-hexene and 4,4-dimethyl-1- and 4,4-dimethyl-2-pentene. Each of the 2-enes exists in cis and tram forms. The first two pairs, which are homologous, have Ci to trans-C2 isomerization enthalpies of ca —13 (for two measurements of trans-4-methyl-2-pentene) and —14.4 kJmol-1, and Ci to cis-C2 isomerization enthalpies of —9.6 and —10.4 kJmol-1. The third pair, not homologous with any other, has a Ci to trans-C2 isomerization enthalpy of... 

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... 

While the vast majority of alkenes reported on the surface of insects are straight-chain molecules, there have been a few reports of methyl-branched alkenes. Warthen and Uebel (1980) found (Z)-2-methyl-24-hexatriacontene in the hydrocarbons of the house cricket, Acheta domesticus. Carlson and Schlein (1991) reported 19,23-dimethyltriacont-l-ene and other homologs in tsetse flies. Howard et al. (1990) found a homologous series of... 

Like alkanes, alkenes can form continuous chain and branched-chain structures. They also form a homologous series. As well, they are nonpolar, which gives them physical properties similar to those of alkanes. 

Data Interpretation. Interpretation of these results is based on specific distinctions among biogenic, pyrogenic and petrogenic hydrocarbons. Biogenic hydrocarlxjns exhibit discrete sets of n-alkanes and alkenes, whereas petroleian contains the homologous series of nr-alkanes, branched and cyclic alkanes and substituted polynuclear aromatic hydrocarbons. A predominance of specific... 

Naming alkynes Straight-chain alkynes and branched-chain alkynes are named in the same way as alkenes. The only difference is that the name of the parent chain ends in -yne rather than -ene. Study the examples in Table 21.6. Alkynes with one triple covalent bond form a homologous series with the general formula C H2 -2-... 

Another approach to create diverse C—H bond functionalization is to combine one C—H bond activation with a subsequent transformation which greatly enriches the diversity of the initial C—H bond functionalization products. Bearing this concept in mind, Sharma and Hartwig recently developed a one-pot process involving the linear selective Pd-catalyzed allylic C—H bond oxidation and subsequent enantioselective branched Ir-catalyzed allylic substitution to form products with new C—O, C—N, C—C, and C—S bonds (Scheme 5.67). The utility of this process was further demonstrated by an iterative sequence of C—H bond functionalization and homologations to prepare enantioenriched (l,n)-functionalized alkenes. 

The methods discussed for separation of alkanes and cycloalkanes from alkenes, aromatics, resins and other more polar constituents of petroleum can be employed also for synthetic mixtures, asphalts, bitumens, etc. However, for the quantification and identification of such homologous families as n-alkanes, branched alkanes, etc., further analysis is needed. Whereas the GTA relates to functionality and differences in polarity, the separation within the alkane family cannot be based on these characteristics. 

Hydroformylation is a reaction process wherein both hydrogen and a formyl group are introduced to an unsaturated bond, especially an olefmic bond. A typical example of this process is the reaction of 1-alkenes with carbon monoxide and hydrogen catalyzed by cobalt or rhodium complexes to give the corresponding homologous aldehydes. It should be noted that both linear and branched aldehyde... 

In the late 1930s, Otto Roelen at Ruhrchemie discovered hydroformylation, sometimes called the 0x0 process, one of the first commercially important reactions to use a homogeneous catalyst. He found that an alkene can be converted to the homologous linear n) and branched iiso) aldehydes (eq. 20) by the addition of H2 and CO, catalyzed by Co2(CO)8 further reduction of the aldehydes to the alcohols is observed under some conditions. Today, 4 million ton of aldehydes are made annually in this way. 

For alkenes (Table 3.3), alkynes, and arenes, the concept of homology as pertains to addition of alkyl substituents also continues to apply, although positional isomerism and stereochemistry play important roles. Addition of further carbon-carbon double bonds, triple bonds, and/or aryl groups, as well as branching, confounds widespread prediction however, in a closely related series, the principle is maintained. 

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