Question

when do i know to use atom size, electronegativity, inductive, resonance or hybrization to determine acid stength? please explain.

Answer 1

acidic strength is determined by the stability of its conjugate base. the more stable the conjugate is higher will be its acidic strength

To determine the acidic strength follow the following emprical rule -

1. if the key atom (atom in which the effect is considered) is different , then always decide according to the electronegativity. since the conjugate base of acid is negatively charged , hence more electronegative the atom is , higher will be the stability and greater will be the acidic strength

eg if we consider (I)and (II)

taking the conjugate base of both andd checking the stability and

we know that O is more electronegative than N hence is more stable than hence the acidic strength is >

2. if the key atom is same , then check hybridization. as we know electronegativity of SP hybrid orbital is more than SP2 and it is more than sp3 (higher the %s character of the orbital is , higher will be the electronegativity is ) . acidic strength then follows the order

sp > sp2 > sp3

3. if the key atom is same and hybriization is same , then check for the electronic effect viz. inductive effect , mesomeric effect and hyper conjugation etc

In electronic effect , electron withdawing group increases the stability of negative charge whereas electron releasing group decreases the stability .

power of electronic effect follows the order

Resonance (-R or -M) > hyper conjugation(-H) > Inductive effect (-I)

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