ABSTRACT
This chapter looks at covalent bonds that exhibit a degree of polarisation and the manner in which they may be broken. Homoatomic bonds tend to prefer homolytic bond fission, which results in radicals being formed; while heteroatomic bonds often undergo heterolytic bond fission, which results in ions being formed. In the case of dinitrogen and dioxygen, the multiple bonds were homoatomic, and so there is no permanent polarisation across the central bond. One of the commonest heteroatomic multiple bond systems in which carbon partakes involves oxygen. When multiple bonds alternate with single bonds, the arrangement is called a conjugated system. Whole units of charge can be transmitted along a conjugated system by the redistribution of the electrons present in the double and single bonds as a result of the mesomeric effect. Conjugated systems that have an electron sink at one end and an electron source at the other, usually have a permanent dipole that is established by the mesomeric effect.
