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The Pentane Molecule

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Molecular structure

The conformation (shape) of pentane is linear, similar to that of butane, but one carbon atom longer.

Isomers

Pentane is one of three structural isomers with the molecular formula C5H12, the others being isopentane and neopentane.The branched isomers are more stable than pentane, which means that they have lower heat of formation and heat of combustion. Isopentane is more stable than pentane by 1.8 kcal/mol, and neopentane by 5 kcal/mol.[1] A related cycloalkane is cyclopentane, although this is not an isomer of pentane as its molecular formula is different, cyclopentane is an isomer of the pentenes.

Uses

Being an unfunctionalized hydrocarbon, pentane is a commodity chemical. It is mainly a fuel and a solvent, although it also could be used as a source of H2 via steam reforming. As the most volatile hydrocarbon that is liquid at room temperature, pentane is often used in the laboratory as a solvent that can be conveniently evaporated. Also because of its nonpolarity and lack of functionality, its dissolving power is poor, thus only non-polar or alkyl-rich compounds are soluble in it. Pentane is completely miscible, however, with many common solvents such as chlorocarbons, aromatics, ethers, but not short chain amines or short chain alcohols.

Reactions

Pentane burns to form carbon dioxide and water:

C5H12 + 8 O2 --->5 CO2 + 6 H2O

When oxygen is limited, carbon, partially oxidized carbon (soot), and carbon monoxide are also formed.

As for other hydrocarbons, pentane undergoes free radical chlorination:

C5H12 + Cl2 --->C5H11Cl + HCl

Such reactions are unselective, yielding a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur. Whereas n-butane is the conventional feedstock in duPont's synthesis maleic anhydride, pentane is also a substrate:

CH3CH2CH2CH2CH3 + 5 O2 --->C2H2(CO)2O + 5 H2O + CO2

References

  1. From the values listed at Standard enthalpy change of formation (data table).

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