Isoparaffins (Table A-14) are paraffins in which branching is present, usually at the number 2 carbon atom, although branching can take place at a different position in the chain, although such molecules are not strictly isoparaffins. Isoparaffins (branched paraffins) have a boiling point lower than normal paraffin with same number of carbon atoms, and generally, the greater the branching, the lower the boiling point (Table A-14).
Table A-14 Physical properties of selected branched paraffins.
| Paraffin | Melting point, °C | Boiling point, °C | Density, g/ml @20 °C |
|---|---|---|---|
| Isobutane | -159 | -12 | |
| Isopentane | -160 | 28 | 0.620 |
| Neopentane | -17 | 9.5 | |
| Isohexane | -154 | 60 | 0.654 |
| 3-Methylbutane | -118 | 63 | 0.676 |
| 2,2-Dimethylbutane | -98 | 50 | 0.649 |
| 2,3-Dimethylbutane | -129 | 58 | 0.668 |
Octane number is a measure of the ability of a fuel (gasoline) to avoid knocking. The test engine is adjusted to give knock from the fuel rated. Then, various mixtures of isooctane (2,2,4-trimethylpentane) and n-heptane are used to find the ratio of the two reference fuels that will give the same intensity knock as that from unknown fuel. Defining isooctane as having an octane number of 100 and n-heptane as 0, the octane number is the volumetric percentage of isooctane in heptane that matches knock from the unknown fuel is reported as octane number of the fuel.
Unsaturated aliphatic hydrocarbon derivatives (olefin derivatives) (Table A-15) have one or more double bonds between carbon atoms. Also, olefin derivatives have different types of isomers – for example, butene (C4H8) isomers have many arrangements which include 1-butene (CH3CH2CH=CH2), cis 2-butene (cis-CH3CH=CHCH3), trans 2-butene (trans-CH3CH=CHCH3), and isobutene [(CH3)2CH=CH2].
Table A-15 Physical properties of selected olefins.
| Olefin | Melting point, °C | Boiling point, °C | Density, g/ml @20°C |
|---|---|---|---|
| Ethylene | -169 | -102 | |
| Propylene | -158 | -48 | |
| 1-Butene | -6.5 | ||
| 1-Pentene | 30 | ||
| 1-Hexene | -138 | 63.5 | 0.643 |
| 1-Heptene | -119 | 93 | 0.675 |
| 1-Octene | -104 | 122.5 | 0.698 |
| 1-Nonene | 146 | 0.716 | |
| 1-Decene | -87 | 171 | 0.731 |
| Cis-2-butene | -139 | 4 | 0.743 |
| Trans-2-butene | -106 | 1 | |
| Isobutylene | -141 | -7 | |
| Cis-2-pentene | -151 | 37 | |
| 2-Methyl-2-butene | -123 | 39 | 0.655 |
| 2,3-Dimethyl-2-butene | -74 | 73 | 0.660 |
| Cyclopentene | -93 | 46 | 0.705 |
| Cyclohexene | -104 | 83 | 0.774 |
| 1,3-Cyclopentadiene | -85 | 42 | 0.810 |
| 1,3-Cyclohexadiene | -49 | 87 | 0.798 |
| 0.847 |
Owing to the presence of a double bond, the alkene undergoes a large number of addition reactions, but under special conditions, they also undergo substitution reactions. Alkene is readily hydrogenated under pressure in the presence of a catalyst. Platinum and palladium are effective at room temperature. Addition polymerization occurs between molecules containing double or triple bonds. The following are some reactions of aliphatic hydrocarbons to enhance its