What Is Neopentane?
Neopentane is an alkane with a 5-carbon branched chain with two side chains.
Neopentane is a colorless gas, but becomes liquid on cold days. Structural isomers of neopentane include n-pentane and isopentane.
However, in contrast to the structural isomers n-pentane and isopentane, neopentane has a high melting point and a low boiling point, making it an unstable compound in state.
Uses of Neopentane
The main use of neopentane is as a foaming agent. It is also used as an electronics cleaner and chemical solvent. A foaming agent is an agent used to form cellular structures by adding other compounding agents to polymers, such as rubber and plastics, and allowing the inclusion of gases and other substances generated by thermal decomposition.
Neopentane is used not only in the production of styrene foam but also in the manufacture of urethane and other materials, and is therefore incorporated into everyday household products. Neopentane is obtained by fractional distillation from crude oil or petroleum hydrocarbon cracking oil.
Properties of Neopentane
Neopentane is soluble in ethanol and ether, but insoluble in water. The boiling point of neopentane at ambient pressure is 9.5°C. At normal temperature and pressure, neopentane exists as a highly flammable gas. In contrast, in cold weather and under high pressure, neopentane is a volatile liquid.
Structure of Neopentane
The structure of neopentane takes the form of methane with all four hydrogen atoms replaced by methyl groups. Neopentane’s chemical formula is C5H12, its molar mass is 72.15, and its specific formula is (CH3)4C.
The IUPAC systematic name for neopentane is 2,2-dimethylpropane, but neopentane is used as the IUPAC-accepted common name.
Other Information on Neopentane
1. Reasons for Neopentane’s Low Boiling Point
Compared to the other structural isomers, the boiling point of neopentane is very low. At ambient pressure, isopentane has a boiling point of 27.7°C and n-pentane has a boiling point of 36.0°C. Neopentane has a boiling point of 9.5°C, which is very low. Neopentane is a gas at room temperature and atmospheric pressure, while its structural isomers isopentane and n-pentane are liquids.
The reason for the low boiling point of neopentane is the weak action of intermolecular forces in neopentane. In other words, the reason is that as the number of branched chains increases, the shape of the molecule becomes more spherical and the surface area of the molecule is reduced compared to that of the linear chain.
2. Reason for the high melting point of Neopentane
Neopentane has a melting point of -16.6°C at ambient pressure. The melting point of the structural isomer isopentane is -159.9°C and that of n-pentane is -129.8°C. Thus, the melting point of neopentane is about 140°C higher than that of isopentane and about 110°C higher than that of n-pentane.
It has been explained that the reason for the unusually high melting point of isopentane is due to the strong intermolecular forces acting on it in the solid state. In other words, since the neopentane molecule is tetrahedral, it is closely packed in the solid phase, and thus the strong intermolecular forces are thought to be at work. However, the reason has been questioned because of the lower density of neopentane than the other two structural isomers.
It has also been suggested that the higher melting point of neopentane is due to entropy effects caused by the high molecular symmetry of neopentane. This is because the melting entropy of neopentane solids is lower than the melting entropy of its structural isomers, n-pentane, and isopentane. In fact, the melting entropy of neopentane is about four times lower than that of its structural isomers, n-pentane and isopentane.
3. Neopentyl Group
The structure of neopentane with one hydrogen removed is called a neopentyl group. The neopentyl group is often abbreviated as Np and sometimes abbreviated as Me3C-CH2.
For example, neopentyl alcohol can also be represented as Me3CCH2OH or NpOH.