2.3- Dimethyl-2-butene,

Dimethyl 1 butene 2 3 Dimethyl 2 butene (minor product) (major product)... 

The major product is 2 3 dimethyl 2 butene It has a tetrasubstituted double bond and IS more stable than 2 3 dimethyl 1 butene which has a disubstituted double bond The major alkene arises by loss of a hydrogen from the p carbon that has fewer attached hydrogens (C 3) rather than from the p carbon that has the greater number of hydrogens (C 1) ... 

Water may remove a proton from either Cl or C 3 of this carbocation Loss of a proton from C 1 yields the minor product 2 3 dimethyl 1 butene (This alkene has a disubstituted double bond )... 

A mixture of three alkenes was obtained m 80% yield having the composition shown The alkene having the same carbon skeleton as the starting alcohol 3 3 dimethyl 1 butene constituted only 3% of the alkene mixture The two alkenes present in greatest amount 2 3 dimethyl 2 butene and 2 3 dimethyl 1 butene both have carbon skeletons different from that of the starting alcohol... 

Reaction of 2,3-dimethyl- 1-butene with HBr leads to an alky) bromide, CfcH Br. On treatment of this alkyl bromide with KOH in methanol, elimination of HBr to give an alkene occurs and a hydrocarbon that is isomeric with the starting alkene is formed. What is the structure of this hydrocarbon, and how do you think it is formed from the alkyl bromide ... 

From 3,3-dimethyl-2-butanol, the major product of rearrangement is 2,3-dimethyl-1-butene. The distribution of the primary dehydration products is far from equilibrium. The maximum ratio of 2,3-dimethyl-1-butene to 2,3-dimethyl-2-butene obtained from 2,3-dimethyl-2-butanol is about 10. This is higher than that to be expected if a proton is removed from the l,l,2-trimethyl-2-propyl carbonium ion in a statistical manner. The maximum ratio of the two olefins obtained from 2,3-dimethyl-2-butanol is also about 10. Hence it can be argued that the high yield of 2,3-dimethyl-1-butene from 3,3-dimethyl-2-butanol does not necessarily rule out a classical carbonium ion mechanism. It is very unlikely, however, that the same intermediate is involved from both alcohols. If such were the case the product of dehydration of 2,3-dimethyl-2-butanol would contain appreciable amounts of 3,3-dimethyl-l-butene. 

W(CH3CN)(C0)3(TPPMS)2] was obtained in the reaction of TPPMS and [W(CH3CN)3(C0)3], and was used as catalyst in hydrogenation of benzene in water/heptane biphasic systems [164]. At 100 °C and 70 bar H2 the catalytic activity was found rather low (average TOP 1 h ). The same complex is also active in the hydrogenation of olefins (e.g. 1-hexene, 2,3-dimethyl- 1 -butene). 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

A new, selective catalyst was reported for the dimerization of propylene to 2,3-dimethylbutenes that are valuable intermediates in the manufacture of specialty chemicals.44 The catalyst is composed of nickel naphthenate, Et3Al, a phosphine, a diene, and chlorinated phenol. Either 2,3-dimethyl-1-butene or 2,3-dimethyl-2-butene can be selectively produced by controlling the catalyst composition. 

SAMPLE SOLUTION (a) Dehydration of 2,3-dimethyl-2-butanol can lead to either 2,3-dimethyl-1-butene by removal of a C-1 hydrogen or to 2,3-dimethy 1-2-butene by removal of a C-3 hydrogen. 

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