The following are equivalent ways of asking about the acidity of an H atom: • What is t...

The following are equivalent ways of asking about the acidity of an H atom:

• What is the most acidic H on the molecule?

• Which H is associated with the published pK_a value?

• Which H on the molecule is easiest to remove?

• Which H on the molecule takes the least energy to remove?

• Which bond to an H is most polarized?

• For which H atom is removal least uphill in energy?

• Which bond to an H atom, when broken, results in the lowest PE conjugate base?

We will often find the last of these questions is easiest to answer. To do this, find all the different H atoms on the molecule, and draw all possible conjugate bases. Only the lowest-energy one is the “real” conjugate base. Identify this structure, and you have found the most acidic H.

Use this strategy to find the most acidic H on each of the following molecules. Note: Each structure as at least three different kinds of H’s, so draw at least three unique conjugate bases for each.