Neopentane

The photolysis of neopentane has been studied by Lias and Ausloos at 1236 and 1470 A. The two main processes which occur are molecular methane elimination from, and fragmentation of, the excited neopentane. The products of photolysis are methane, isobutene, hydrogen, ethane, and propene, with smaller amounts of isobutane, ethylene, propane, acetylene and 2,2-dimethylbutane. The suggested reactions are 

The photolysis of neo-CsHi2-neo-C5Di2 mixtures in the presence of free-radical inhibitors yields methanes CH4 and CD4 only, while in the absence of inhibitors these mixtures yield the additional methanes CD3H and CH3D. The latter products apparently arise from a free-radical process involving the methyl radical, whereas the monoisotopic methanes come from a molecular elimination. The presence of methyl radicals in the photolysis was clearly shown by the formation of CD3H in the photolysis of neo-C5Di2 H2S mixtures. 

Ethane, which is a major product in the absence of inhibitors, is completely eliminated as a product in the presence of NO or H2S. This observation, combined with the fact that the ethanes formed in the photolysis of neo-C5Hi2-neo-C5Di2 mixtures are entirely C2H6, CH3CD3 and CjDg, indicates that ethane is formed only from the combination of methyl radicals. 

Isobutene comprises the largest fraction of product and is the compound expected from molecular methane elimination. There is, however, always more iso- 

Through scavenging of D atoms by HjS in the photolysis of neo-C5Di2 it was found that the hydrogen formed is approximately equal to the excess isobutene. 

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Engstrom J R, Goodman D W and Weinberg W H 1988 Hydrogenolysis of ethane, propane, n-butane and neopentane... 

Three isomeric alkanes have the molecular formula C5H12 The unbranched isomer is as we have seen n pentane The isomer with a single methyl branch is called isopen tane The third isomer has a three carbon chain with two methyl branches It is called neopentane... 

Hexane (CH3CH2CH2CH2CH2CH3) > pentane (CH3CH2CH2CH2CH3) > isopentane [(CH3)2CHCH2CH3] > neopentane [(CH3)4C]... 

Nanotube (Section 11 8) A form of elemental carbon com posed of a cyhndncal cluster of carbon atoms Neopentane (Section 2 10) The common name for 2 2 dimethylpropane (CH3)4C... 

There are three isomeric pentanes, ie, saturated aHphatic hydrocarbons of molecular formula C H 2- They are commonly called / -pentane [109-66-0] isopentane [78-78-4] (2-methylbutane), and neopentane [463-82-1] (2,2-dimethylpropane). 

Tetraneopentyltitanium [36945-13-8] Np Ti, forms from the reaction of TiCl and neopentyllithium ia hexane at —80° C ia modest yield only because of extensive reduction of Ti(IV). Tetranorbomyltitanium [36333-76-3] can be prepared similarly. When exposed to oxygen, (NpO)4Ti forms. If it is boiled ia ben2ene, it decomposes to neopentane. When dissolved ia monomers, eg, a-olefins or dienes, styrene, or methyl methacrylate, it initiates a slow polymerisation (211,212). Results from copolymerisation studies iadicate a radical mechanism (212). Ultraviolet light iacreases the rate of dissociation to... 

Figure 4.2. Rotational-energy barriers as a function of substitution. Tbe small barrier ( 2kcal) in ethane (a) is lowered even further ( O.Skcal) if three bonds are tied back by replacing three hydrogen atoms of a methyl group by a triple-bonded carbon, as in methylacetylene (b). The barrier is raised 4.2 kcal) when methyl groups replace the smaller hydrogen atoms, as in neopentane (c). Dipole forces raise the barrier further ( 15 kcal) in methylsuccinic acid (d) (cf. Figure 4.3). Steric hindrance is responsible for the high barrier (> 15 kcal) in the diphenyl derivative (e). (After...

Saturated hydrocarbons such as neopentane, notbomane, and cyclooctane have been converted to the corresponding perfluoro derivatives in 10-20% yield by gas-phase reaction with fluorine gas diluted with helium at —78°C. Simple ethers can be completely fluorinated under similar conditions. Crown polyethers can be fluorinated by passing an Fa/He stream over a solid mixture of sodium fluoride and the crown ether. Liquid-phase fluorination of hydrocarbons has also been observed, but the reaction is believed to be ionic, rather than radical, in character. A variety of milder fluorination agents have been developed for synthetic purposes and will be discussed in Chapter 6 of Part B. 

Direct photochemical excitation of unconjugated alkenes requires light with A < 230 nm. There have been relatively few studies of direct photolysis of alkenes in solution because of the experimental difficulties imposed by this wavelength restriction. A study of Z- and -2-butene diluted with neopentane demonstrated that Z E isomerization was competitive with the photochemically allowed [2tc + 2n] cycloaddition that occurs in pure liquid alkene. The cycloaddition reaction is completely stereospecific for each isomer, which requires that the excited intermediates involved in cycloaddition must retain a geometry which is characteristic of the reactant isomer. As the ratio of neopentane to butene is increased, the amount of cycloaddition decreases relative to that of Z E isomerization. This effect presumably is the result of the veiy short lifetime of the intermediate responsible for cycloaddition. When the alkene is diluted by inert hydrocarbon, the rate of encounter with a second alkene molecule is reduced, and the unimolecular isomerization becomes the dominant reaction. 

With the five-carbon alkane, pentane, there are three ways to draw the structural formula of this compound with five carbon atoms and twelve hydrogen atoms. The isomers of normal pentane are isopentane and neopentane. The structural formulas of these compounds are illustrated in Table 2, while typical properties are given in Table 1. 

Sterically crowded molecules, like neopentane, are too unstable. 

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