2- pentene isomers

Draw and name the 6 pentene isomers, C5HK3, including ,Z isomers. 

Additional adsorption sites are provided on open metal sites, when available. [Cu3(BTC)2] is performant in the selective adsorption and separation of olefinic compounds. The highly relevant separations of propene from propane and of isobutene from isobutane have been accomplished with separation factors of 2.0 and 2.1, respectively [101, 102]. [Cu3(BTC)2] also selectively takes up pentene isomers from aliphatic solvent in liquid phase, and even discriminates between a series of cis- and trans-olefin isomer mixtures with varying chain length, always preferring a double bond in cis-position. This behavior is ascribed to tt -complexation with the open Cu sites [100]. 

When the pentene isomers are hydrogenated (Table 11.1) the results show that the order in the rates of hydrogenation derived from rate constants over a 1% PCI/AI2O3 catalyst is ci5-2-pentene > 1-pentene iran5 -2-pentene. 

However if the cw-2-pentene isomer or the 1-pentene isomer is added first, the rate of alkyne hydrogenation is unaffected. The iraui -molecule acts as a poison for the alkyne hydrogenation whereas the cis- and 1-pentene isomers have no effect. 

Compositions of metathesis reaction mixtures obtained over a range of conversions starting with cis- and trans-4-methyl-2-pentene are shown in Figs. 1 and 2, respectively. Certain important differences are evident in comparisons with the course of reactions of 2-pentene isomers (18). 

It would be tempting to apply the same rationale to the metathesis of 2-pentene isomers, but clearly, the steric requirements of methyl and ethyl are much less than that of isopropyl, and trade-offs involving cis-1,2-disubstitution vs. axial orientation are not clear neither is the important role of catalyst ligand influence. 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

How many pentene isomers exist How many isomerization reactions would describe their isomerizations ... 

Problem 6.7 Supply structural formulas and systematic names for all pentene isomers including stereoisomers. 

Skeletal isomerization requires higher temperature and stronger acid catalysts than do double-bond migration and cis-trans isomerization. Butylenes, for example, are transformed to isobutylene over supported phosphoric acid catalysts.98 The equilibrium mixture at 300°C contains approximately equal amounts of straight-chain and branched butenes. Similar studies were carried out with pentene isomers.99 Side reactions, however, may become dominant under more severe conditions.100... 

Ethylene, propylene, a mixture of internal pentene isomers, 1-hexene and 1-decene all give a mixture of predominantly C.-C olefins (Table III). 

The product pentene isomers from the C -C.Q olefin charge stocks also all approach equilibrium, as shown in Table V. 

Both T-substituted 1-pentene and 3-methyl-1-butene were observed in yields comparable to the other T-pentene isomers. This observation clearly indicates that the primary source of T-pentene in these systems is through the loss of H atoms from the excited radicals formed by hot tritium addition with opening of the cyclopropane ring. The almost lack of isomerization of the T-substituted parent molecule set an upper limit for the energy left in the T-substituted parent molecule due to the reaction with energetic tritium the upper limit is equal to the activation energy for isomerization (65 kcal mol for cyclopropane and methylcyclopropane and about 62 kcal mol for ethylcyclopropane and dimethyl-cyclopropane. ... 

There is also some evidence from the stereochemistry of trapping with methanol that suggests that 5-(trimethylsilyl)-l-methyl-2,5-diphenyl-l-siIacyclopenta-1,3-diene is in thermal equilibrium with its silabicyclo[2.1.0]pentene isomer (equation 107)235. 

An example of the Zaitsev elimination is the formation bromopentane. A mixture of pentene isomers are produced.4,5... 

Total reaction cross-sections for parent ions of five pentene isomers [132]... 

In discussing processes in olefins, it is convenient to divide the reactions into two classes simple particle transfer and carbon-addition reactions. The relative importance of these two types of reaction is also dependent on the structure of the reactants. The presence of the isobutene type structure (CH2=C(CH3)CH2—) in either the reactant ion or neutral molecule favours the simple particle transfer reaction, mainly because of the large cross-section for the formation of parent-plus-one ions. The 2-butene neutral molecule is more like isobutene than 1-butene with regard to the relative importance of simple particle transfer and carbon addition reactions [284]. However, the magnitude of the cross-section for simple particle transfer reactions in 2-butene (2-P + 2-M reaction) is much closer to that in 1-butene (1-P + 1-M reaction) than to that in isobutene (iso-P + iso-M reaction) [284, 299]. The same is true for pentene isomers i.e. the cross-sections for simple particle transfer reactions in 1-pentene and 2-pentenes are almost the same and are much lower than that in 2-methyl-l-butene. The simple particle transfer cross-sections for other branched pentenes, i.e. 2-methyl-2-butene and 3-methyl-l-butene, are even smaller than those for 1- and 2-pentenes, while the proportion of transfer reactions is higher than the corresponding proportions for 1- and 2-pentenes. The proportion is, of course, highest for 2-methyl-l-butene which has the isobutene type structure. 

With pentene isomers, the carbon addition products are mainly Cg, C7 and Cg ions [132, 290]. However, Cg ions are absent in branched pentenes except for 2-methyl-l-butene where Cg ions constitute more than 10% of the total product ions at 1.7 eV ion exit energy [132]. No Cg ions are observed in any of the isomers [132, 290]. The photoionization study by Koyano et al. [132] reports an observation of a very small concentration of dimeric ion(s) (Cj 0 ion(s)) with all of the pentene isomers. With hexenes, the main carbon addition products are C7, Cg and C9 ions [290], the relative importance of these ions being dependent on the structure. The relative probabilities of these carbon addition reactions... 

Tau et al. also converted syngas that contained [l- C]-l-pentene or a mixture of [2- C]-cis-2- plus [2- C]-tra/ir-2-pentene. Incorporation of to produce C-labeled Cg+-products was low. More surprising, the amount of isomerization of the added 1-pentene to the more stable internal pentene isomers was too small to detect (Figure 19). Thus, when [1- C]-1-pentene is added, the PC trace in Figure 19 clearly shows the presence of 1-pentene but neither Relabeled cis-2- nor trans-2-pentene can be seen likewise, when cis- + trans-2-pentene is added, no evidence for R RC-labeled 1-pentene is obtained. More surprising, the amount of R RC-labeled pentane is below the detection level when either C-labeled pentene isomer is added to the synthesis gas. When [l-R RC]-l-decene was added to the syngas, the product contained signifi-... 

A common intermediate step was suggested, confirmed by the similarity, C4-C7, of the final products from the oligomerization of ethene, propene, a mixture of internal pentene isomers, hex-l-ene, and dec-l-ene over a zeolitic catalyst. ... 

An interesting sidelight of this work is the use of the magnetized carbon described herein as an olefin isomerization catalyst. In the presence of this material we have been able to form thermodynamically less stable methyl pentene isomers at elevated temperatures. 

Olefins which undergo this reaction are 1-butene, 2-butene, isobutylene, a mixture of pentene isomers, diisobutylene, and tetrapropylene. Coffield et al. 82, 83) have shown that acetylene and manganese pentacarbonyl under 600 psi and at 150° C give l,2-(propenylene)cyclopentadienylmanganese tricarbonyl. The conditions of this synthesis are similar to those described by Reppe 84) for the reaction of acetylene with other metal carbonyls to form iT-bonded complexes. 

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