IB Chemistry R3.3 Notes

The third reaction type you need to know about is electron sharing, which typically takes the form of free radical substitution. This occurs in alkanes because they have no functional group and consist purely of C-C and C-H bonds. As a result, their general formula is C_nH_2n+2.

Due to their structure, alkanes are non-polar so they only have weak London dispersion forces, making them volatile and insoluble in water. However, the high strength of the C-C and C-H bonds makes them unreactive.

Thus, the only reactions they undergo are with very reactive species called radicals. Thus, during free radical substitution, alkanes reacts with halogens in the presence of UV light to form a halogenoalkane and hydrogen halide. For example:

C₂H­₆ + Cl₂ → C₂H₅Cl + HCl