INDUCTIVE EFFECTS IN A COVALENT BOND
Chemical reactions take place as a result of giving, taking and/or sharing of electrons. So the different
effects which influence the distribution of electrons in a covalent bond of an organic molecule are
important for understanding the mechanism of the reactions the molecule undergoes. It is important to
note that the driving force behind all of these so-called ‘effects’ is stability and energy minimization.
Inductive Effect
A covalent single bond is made up of two paired electrons. But in cases when the atoms forming the
bond differ in electronegativity (electronegative atoms love electrons) it results in a ‘polarized’ bond
(which means the bonded electrons are shifted towards the more electronegative atom). So a C-N bond in
CH3NH2 (methylamine) would be polarized as follows:
Figure 1. Inductive effects
δ+C—Nδ–, where δ indicates partial charge, not full shift of charge like an ionic bond. So what basically
happens is N pulls the bonded electrons towards it leaving the C slightly positive or electron
deficient. Now if this C-N bond is a part of a bigger chain like in C3H3-C2H2-C1H2-NH2, then due to this
effect, the C next to the N is slightly positive charged. Being positive (electron deficient) it wants more
electrons so it pulls the bonded pair of electrons from the C next to it (C2), which in turn becomes slightly
positively charged as a result. Now the chain electron distribution looks like:
-C-Cδδ+-Cδ+-Nδ–, where δδ+ means less positively charged than δ+. This relay of charge is called Inductive
(I) effect. Since this case involves pulling of electrons which start the whole thing, it is termed –I
effect. We can have +I effect as well which is illustrated as follows:
