Chapter 18, Problem 23P

(a) Write structural formulas and provide IUPAC names for all the isomeric aldehydes and ketones that have the molecular formula ${\text{C}}_{\text{5}}{\text{H}}_{\text{10}}\text{O}$. Include stereoisomers.

(b) Which of the isomers in part (a) yield chiral alcohols on reaction with sodium borohydride?

(c) Which of the isomers in part (a) yield chiral alcohols on reaction with methylmagnesium iodide?

Interpretation Introduction

Interpretation:

The given parts are to be explained.

Concept Introduction:

The systematic naming of organic compound is given by IUPAC. The naming of organic compound is done in such a way that the structure of the organic compound is correctly interpreted from its name.

Rules for writing the structural formula from IUPAC are as follows:

First, identify the word root for the given compound.

The suffix used in the compound like $\text{-ane},\text{ -ene},\text{ -yne},\text{ -ol},\text{ -al}$ and so on.

The position and location of the substituents that are bonded to the carbon chain must

identified and number theses substituents on the basis of their priorities.

Answer to Problem 23P

Solution:

a)

b)

c)

Explanation of Solution

a) Structural formulas and IUPAC name of the isomeric aldehydes and ketones of ${\text{C}}_{\text{5}}{\text{H}}_{\text{10}}\text{O}$.

The constitutional isomers are the isomers that consist of the same chemical formula but the way they attach to their atoms are totally different from each other.

Aldehydes and ketones contain carbonyl $\left(\text{C=O}\right)$ functional group in their parent chain and are named by adding a suffix $\text{-al}$ and $\text{-one}$ respectively. The given molecular formula is ${\text{C}}_{\text{5}}{\text{H}}_{\text{10}}\text{O}$ that shows the presence of five carbon atoms, ten hydrogen atoms, and an oxygen atom. Therefore, the isomeric aldehydes and ketones with this molecular formula along with their IUPAC names can be shown as follows.

b) The isomers that form chiral alcohols on the reaction with sodium borohydride.

The reduction of aldehydes with sodium borohydride results in the formation of a primary alcohol, whereas in ketones the formation of secondary alcohols is taken place. Primary alcohols are not chiral in nature. On the other hand, the secondary alcohols that are formed from unsymmetrical ketones show chirality. Therefore, among the isomers in part (a), $\text{pentan-2-one}$ and $\text{3-methylbutan-2-one}$ yield chiral alcohols after treating with sodium borohydride. The structures these isomers are:

c) The isomers that give chiral alcohols on reaction with methylmagnesium iodide.

Methylmagnesium iodide is also known as the Grignard reagent. Aldehydes can give chiral alcohols on reaction with methylmagnesium iodide. The formation of chiral and achiral molecules from the isomers that are present in part(a) are shown as:

Hence, the isomers that form chiral alcohols on reaction with methylmagnesium iodide are shown below.