Question

19. Which of the following can undergo keto-enol tautomerism? a. 2,4-dimethyl-3-pentanoneb. 2.2.4,4-tetramethyl-3-pentanone c, both a and b d. neither a norb 20. Which of the following compounds is a tautomer of the following compound? MOH OH OH c. both a and b d. neither a norb 21. Examine the following ball-and-stick models. Atoms other than carbon and hydrogen are labeled with the symbol of the element. How is this reaction classified? a. oxidation b. reduction c. tautormerization d. hemiacetal formation e. none of the above

Answer 1

Keto enol tautomerism is referred to as an equilibrium between a keto form (carbonyl group) and an enol form (an alcohol with an adjacent double bond). It can be shown as

R3 H (6) enol form. Keto form

We can see that only those compounds that have an $\alpha$ H will undergo keto enol tautomerism.

19. (a) is the correct answer.

EXPLANATION -

As we know, the presence of an $\alpha$ H is essential for a compound to undergo keto enol tautomerism.

From the diagram, we can see that 2,4-dimethyl-3-pentanone has 2 $\alpha$ H while 2,2,4,4-tetramethyl-3-pentanone does not have any $\alpha$ H. So the first compound will undergo keto enol tautomerism while the second compound will not.

он 19. а) CH, 1 он | CH3 CH CH3 На | — Н. с нэ CH3 НІ CH3 CH3 CH3 CH 3 ОН 2,4-dimethyl-3-pentanone СН3 — СН3 СН3 Нас | СН3 2,2, 4,4 - tetramethyl-3-pentanone

20. (c) is the correct answer.

EXPLANATION -

The keto enol tautomerism of the given compound is shown as -

20. ои CH Оң (а) (6)

The tautomerism is occuring on both ends of the double bond as they are two different enol groups.

So both are tautomers.

21.(c) is the correct answer.

EXPLANATION -

The first ball-and-stick model is of a keto group and the second is of an enol group. There is an equilibrium established between the two forms (shown by $\rightleftharpoons$ ). From the first diagram, we know that this process is known as keto enol tautomerism or simply tautomerism.