The pKa values of acetone and 1-phenyl-2-propanone are 26.5 and 19.8 respectively. Use electronic factors to...

The pKa values of acetone and 1-phenyl-2-propanone are 26.5 and 19.8 respectively. Use electronic factors to explain this order of values.

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Expert Solution

Pka notation is shown for the strength of the acid. Mathematical expression of pka is

pka = - log ka . Equilibrium constant ka of acid shows degree of dissociation and in so the strength of acid. Larger the value of it , stronger will be an acid.

According to the mathematical expression, larger the value of ka smaller will be its pka value.

We are given two compounds. First is acetone and other is 1-phenyl-2-propanone.

The given pka values shows that 1-phenyl-2-propanone is stronger acid than acetone.

To explain it we get a help of resonance and stability of conjugate base.

Strength of acid depends on the stability of conjugate base. Lets ionize both given molecules look for stability of conjugate bases.

After removal of proton from the molecule both get negative charge on their conjugate base.

The conjugate base which can delocalize that negative charge more that will be stable base.

The delocalization is shown by using resonance structure.

We can see there are 6 resonance structures that are formed from conjugate base of 1-phenyl-2-propanone. So it could delocalize more effectively and so is it stronger acid than acetone.

queen_honey_blossom answered 1 year ago

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