Question

Provide a brief explanation for the following experimental observations:
a) The pKa value of H2SO4 is lower than the one of H2SO3. Estimate the expected pKa values in water. b) The gas phase proton affinity of benzophenone is larger than the one of acetone.
c) 4-Dimethylaminopyridine, DMAP, is a stronger Brønsted base than pyridine.
d) Anhydrous phosphoric acid, H3PO4, exhibits electrical conductivity.
e) Dimethylsulfoxide, DMSO, binds to AlCl3 via the oxygen atom but to AgCl via the sulfur atom

Answer 1

Provide a brief explanation for the following experimental observations:
a) The pKa value of H2SO4 is lower than the one of H2SO3. Estimate the expected pKa values in water.

pKa --------- determine dissociation of an acid.

if Ka = x, pKa = -log(x)

, Ka = 1x10^-7,

pKa = 7,

Ka of 1x10^-7 is the Ka of water, -----------------------is neutral

strong acid, Ka > 1, pKa < 1 smaller the pKa value, the stronger the acid

H2SO4 = -3
H2SO3 = 2..

The pKa value of H2SO4 is lower than the one of H2SO3.

it is due to the lack of that 1 oxygen making H2SO3 a weaker acid

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b) The gas phase proton affinity of benzophenone is larger than the one of acetone.

The gas phase proton affinity of benzophenone is larger than the one of acetone due to

a) the stronger the base

and

b) the weaker the conjugate acid in the gas phase

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c) 4-Dimethylaminopyridine, DMAP, is a stronger Brønsted base than pyridine.

4-dimethylaminopyridine (DMAP) may appear to be a base similarity in strength to pyridine or N,N-dimethylaniline,

But it is actually more than ten thousand times stronger, due to charge delocalization in its conjugate acid.

It is used as a catalyst for acyl transfer reactions.