Chapter 2, Problem 47P

Interpretation Introduction

Interpretation: Structures of the possible isomeric heptanes should be drawn with names.

Concept introduction: Molecules that possess identical molecular formula but vary in the manner of their connectivity of the bonds are referred as structural isomers. These are essentially found in alkanes that can be branched by removal of $\text{H}$ group and its replacement with some alkyl group.

For instance, smallest branched alkane possible is $\text{2-methylpropane}$ . Its molecular formula is identical with butane ${\text{C}}_{\text{4}}{\text{H}}_{\text{10}}$ but it has different connectivity. The molecular models of $\text{n-butane}$ and $\text{2-methylpropane}$ are illustrated below.

  

The two compounds infact constitute a pair of constitutional isomers. These kinds of isomers are formed by cleavage and replacement of bonds unlike the conformational isomers that results due to rotation around the bond.

As per IUPAC recommendations longest chain found in a continuous manner in a branched molecule is chosen as parent chain.

The IUPAC name begins with prefix to designate the number of $\text{C}$ atoms in the longest chosen parent alkane followed by the suffix −ane. Positions of side chains or substituents are indicated by the lowest numeral places before prefix.

Names of branches that occur commonly as side chains are listed below: