Inductive and mesomeric effects both play an important role in determining how organic reactions happen through their abilities to stabilise carbocation intermediates.
Inductive effects are the result of the polarisation of electrons in sigma (single) bonds and mesomeric effects are the result of the polarisation of electrons in pi (double) bonds.
Inductive effects
- Negative inductive effects are due to the presence of an electronegative element pulling electron density in a sigma bond towards itself and away from the carbon atom it is bonded to.
- Positive inductive effects occur when a carbon atom is bonded to an electron donating group such as an alkyl group. This is a very significant effect in stabilising carbocation intermediates.
Mesomeric effects
- Positive mesomeric effects are the result of electrons (lone pairs or electron density from a ∏-bond) being donated to stabilise the positive charge on an ion. This gives us resonance forms of the same carbocation.
- Negative mesomeric effects stabilise a negative ion by withdrawing electron density from a ∏-bond.
