Question

The enolic form of acetone contains.
(A) $9$ sigma bonds, $1$ pi bond, and $2$ lone pairs of electron
(B) $8$ sigma bonds, $2$ pi bond, and $2$ lone pairs of electron
(C) $10$ sigma bonds, $1$ pi bond, and $1$ lone pairs of electron
(D) $9$ sigma bonds, $2$ pi bond, and $1$ lone pairs of electron

Answer 1

In order to answer this question, you must be aware of the structures of ketone compounds. Firstly, convert the acetone to an alcohol and then draw its Structure and then observe the structure and count the number of sigma bonds, pi-bonds, and the lone pairs over it. Remember, a single bond represents a $1$ sigma bond and in multiple bonds like double and triple bonds, one of the multiple bonds is always a sigma bond and the rest other bonds that are pi-bonds. Count all the required things and select the correct option.

Complete step-by-step answer: Step 1: In this step, we will convert the acetone to an enolic form:
To convert acetone into enol form, use the keto-enol tautomerism method. In organic chemistry, keto–enol tautomerism refers to a chemical equilibrium between a keto form (a ketone or an aldehyde) and an enol (an alcohol). The keto and enol forms are said to be tautomers of each other. The interconversion of the two forms involves the movement of an alpha hydrogen atom and the reorganisation of bonding electrons; hence, the isomerism qualifies as tautomerism.

Step 2: In this step we will count the no of bonds:
Since we know that, a single bond represents $1$ sigma bond and in multiple bonds like double and triple bonds, one of the multiple bonds is always a sigma bond and the rest other bonds that are pi-bonds.
We have,
number of sigma bonds $= \,\,9$
number of pi – bonds $= \,\,1$
number of lone pairs $= \,\,2$ (only oxygen contains lone pairs in this molecule)

Clearly, the correct answer is Option A i.e. $9$ sigma bonds, $1$ pi bond, and $2$ lone pairs of electrons.

Note: Enols, or more formally, alkenols, are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond.