How many of the numerous eight-carbon alkane constitutional isomers are continuous-chain alkanes?

Interpretation:

The number of eight-carbon alkane constitutional isomers that are continuous-chain alkanes has to be given.

Concept Introduction:

Organic compounds are represented shortly by the molecular formula and structural formula.  Each and every compound has its own molecular formula.  Compounds can have same molecular formula but not same structural formula.

Isomers are the compounds that have same molecular formula but different structural formula.  The main difference lies in the way the atoms are arranged in the structure.  Isomers have different chemical and physical properties even when they have same molecular formula.  This is known as Isomerism.

If there is difference only in the connectivity of the atoms in the molecule, then it is known as constitutional isomerism.  The isomers are known as constitutional isomers.  They will have same molecular formula and same functional group, but they differ in the connectivity between the atoms in the molecule.

Continuous-chain alkane is the one in which all the carbon atoms are bonded in a linear chain (nonbranching chain).

Branched-chain alkane is an alkane which has atleast one branch in its structure that is attached to the continuous chain of carbon atoms.

Constitutional isomers are the compounds which have same molecular formula but they differ only in the connectivity of the atoms in the molecule.  When a straight chain alkane is considered, the branched alkane will be its constitutional isomer.  Therefore, the only possibility of constitutional isomer for straight chain alkane is branched chain alkane only...