Alkanes

ALKANES

Alkanes (also known as paraffins or saturated hydrocarbons) are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles .Alkanes belong to ahomologous series of organic compounds in which the members differ by a constant relative molecular mass of 14. They have 2 main commercial sources, crude oil and natural gas.An alkyl group, generally abbreviated with the symbol R, is a functional group or side-chain that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms, for example a methyl or ethyl group.
PHYSICAL PROPERTIES:
Alkane | Formula | Boiling point [°C] | Melting point [°C] | Density [g·cm3] (at 20 °C) |
Methane | CH4 | -162 | -183 | gas |
Ethane | C2H6 | -89 | -172 | gas|
Propane | C3H8 | -42 | -188 | gas |
Butane | C4H10 | 0 | -138 | gas |
Pentane | C5H12 | 36 | -130 | 0.626(liquid) |
Hexane | C6H14 | 69 | -95 | 0.659(liquid) |
Heptane | C7H16 | 98 | -91 | 0.684(liquid) |
| | | | |
Octane | C8H18 | 126 | -57 | 0.703(liquid) |
Nonane | C9H20 | 151 | -54 | 0.718(liquid) |
Decane | C10H22 | 174 | -30 | 0.730(liquid) |
Undecane | C11H24 |196 | -26 | 0.740(liquid) |
Dodecane | C12H26 | 216 | -10 | 0.749(liquid) |
Icosane | C20H42 | 343 | 37 | solid |
Triacontane | C30H62 | 450 | 66 | solid |
Tetracontane | C40H82 | 525 | 82 | solid |
Pentacontane | C50H102 | 575 | 91 | solid |
Hexacontane | C60H122 | 625 | 100 | solid |

*Alkanes do not conduct electricity, nor are they substantially polarized by an electric field. Forthis reason they do not form hydrogen bonds and are insoluble in polar solvents such as water. 
*An alkane molecule has only C – H and C – C single bonds. The former result from the overlap of a sp³-orbital of carbon with the 1s-orbital of a hydrogen; the latter by the overlap of two sp³-orbitals on different carbon atoms. The bond lengths amount to 1.09×10−10 m for a C – H bond and 1.54×10−10 mfor a C – C bond.
*Virtually all organic compounds contain carbon – carbon and carbon – hydrogen bonds, and so show some of the features of alkanes in their spectra. Alkanes are notable for having no other groups, and therefore for the absence of other characteristic spectroscopic features
*An alkene may be distinguished from an alkane by shaking the hydrocarbon with bromine water.Bromine water is brown or orange, and will lose its colour when it reacts with a double bond in an alkene. Bromine water will stay brown with an alkane because an alkane has no double bonds

CHEMICAL PROPERTIES:
*In general, alkanes show an alkane activity, because their C bonds are relatively stable and cannot be easily broken. Unlike most other organic compounds, they possess no functional groups. Theyreact only very poorly with ionic or other polar substances. However redox reactions of alkanes, in particular with oxygen and the halogens, are possible as the carbon atoms are in a strongly reduced condition; in the case of methane, the lowest possible oxidation state for carbon (−4) is reached.
*Free radicals, molecules with unpaired electrons, play a large role in most reactions of alkanes, suchas cracking and reformation where long-chain alkanes are converted into shorter-chain alkanes and straight-chain alkanes into branched-chain isomers.

*All alkanes react with oxygen in a combustion reaction, although they become increasingly difficult to ignite as the number of carbon atoms increases. The general equation for complete combustion is:
CnH2n+2 + (1.5n+0.5)O2 → (n+1)H2O + nCO2
Inthe absence of sufficient oxygen, carbon monoxide or even soot can be formed, as shown below:
CnH(2n+2) + (n+0.5)O2 → (n+1)H2O + nCO
CnH(2n+2) + (0.5n+0.5)O2 → (n+1)H2O + nC

For example methane:
2CH4 + 3O2 → 2CO + 4H2O
CH4 + 1.5O2 → CO + 2H2O

*Alkanes react with halogens in a so-called free radical halogenation reaction. The hydrogen atoms of the alkane are progressively replaced by...