Organic Chemistry 16
A Ketone (A) gives positive iodoform test. (A) On reduction with Lithium Aluminimum Hydride gives (B) which on heating with phosphoric acid gives (C).
(C) On reaction with Ozone in presence of zinc water gives acetaldehyde and acetone.
Give the total number of atoms present in (A),(B) And (C).
Illustratively if suppose (a) is CH4 then total atoms = 5.
So you need to sum up the total atoms present in A) , B) And C).
The answer is 49.
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1 solution
The trick to start these kind of questions is to grapple them from the end. The last statement says that the compound C on reaction with Ozone gives Acetaldehyde and Acetone.
We know from the mechanism of Ozonolysis reaction that this is only possible if C is 2-methyl but-2-ene . So, number of atoms present in C is 5 + 1 0 = 1 5 .
Now, the second given condition is a clear cut dehydration reaction of alcohols, and since we get C on the dehydration, so by hydrating, we can clearly see that, either the − O H group goes to Carbon-2, or to Carbon-3.
If we assume the attachment of hydroxyl group to carbon-2, then we cannot justify the step of conversion from ketone to alcohol using Lithium Aluminium Hydride. So, clearly the − O H group will be attached to carbon-3 and hence giving us compound B as 3-methyl pent-2-an-2-ol , with number of atoms as 5 + 1 2 + 1 = 1 8
Now, since Lithium Aluminium Hydride converts a carbonyl group to an alcohol group, and so, compound A is nothing but 3-methyl pent-2-an-2-one , which confirms the fact that A is a ketone, giving us the number of atoms in A as 5 + 1 0 + 1 = 1 6 .
So, total number of atoms are 1 5 + 1 8 + 1 6 = 4 9 .