McMurry (Kap 17,4) - Acidity of a-hydrogen atoms: enolate ion formation

Question 1

The hydrogen on the a position of a carbonyl compound is weakly acidic and can be removed by a strong base to yield enolate ion.

Does the presence of a carbonyl compound enchance the acidity of a compound?

Answer 1

Yes, when comparing acetone with ethane, acetone has a more acidic (lower pKa) then ethane, because it contains one carbonyk compound (ketone), whereas ethane does not contain any.

Question 2

How is the enolate ion stabilized?

Answer 2

The negative charge on the carbon is through resonance distributed to the other oxygen atom = resulting in a more stable molecule.

Question 3

Can a weak base form enolate ions?

Answer 3

No only very strong bases can, because carbonyl compounds are very weak acids.

Bases such as LDA is commonly used.

Question 4

Table 17.1 = the pKa of some of the carbonyl compounds. (page 608)

Answer 4

Table 17.1 = the pKa of some of the carbonyl compounds. (page 608)

Question 5

The more carbonyl compounds there is in a molecule - the more acidic the compound becomes.

Answer 5

True - therefore 1,3-diketones are more acidic then water.