What is the inductive effect?

Answer 1

Inductive effect occurs when electron withdrawing groups (EWG) or electron donating groups (EDG) are present, altering the electron density in that region. There are lots of charts available online that show you which functional groups fall into which category. Mainly you will be learning how placing EWG and EDG on benzene and other rings affects how future functional groups attach to the ring(ortho/para or meta directed).

For example, halogens are EWG. They are highly electronegative compared to the carbon they bond to and pull electrons away from the carbon. A snapshot of their polar covalent bond at any moment would likely show a larger concentration of electrons around a chlorine compared to carbon. This causes chlorine to be partially negatively charged and the carbon to be partially positively charged. This shift in electron density is extremely important for reactions; the carbon has been turned into an electrophile because it has a slight electron deficiency, which opens it up to nucleophilic attacks.

It’s also important in terms of stabilization of acids and bases - the more reactive an acid or base, the more stable the conjugate base or acid. In this example, the ring has gained a partial positive charge, increasing its desire to donate a proton, thereby increasing its acidity. An increase in the acidity means an increase in the stability of the conjugate base. In general, EWGs will increase the acidity of the ring. (The reverse is true for EDG, which instead will create a partially negative charge on the carbon because they have long pairs to donate to the ring. This increases the carbons desire to obtain a proton, thereby increasing its basicity as well as susceptibility to electrophilic attacks.)

EWGs inductive effect is said to deactivate the ring because it causes the ring to become electrophilic - this decreases the desire to undergo EAS because electrophiles seek nucleophiles, not other electrophiles. This occurs because the EWG decreases the stability of the ring by disrupting the sigma complex and resonance for the carbocation.

EDGs inductive effect is said to activate the ring because it causes the ring to become nucleophilic - this increases the desire to undergo EAS because the electrophile will seek the nucleophilic ring.

Hope this helps!