Question

Draw the structural formula(s) for the constitutional isomer(s) with the molecular formula C₈H₁₈ that have an unbranched chain. (There are four possible isomers)

Answer 1

STRUCTURAL FORMULA

The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly. Unlike chemicalformulas, structural formulas provide a complete geometric representation of the molecular structure. For example, many chemical compounds exist in different isomeric forms, which have different enantiomeric structures but the same chemical formula. A structural formula is able to indicate arrangements of atoms in three dimensional space in a way that a chemical formula may not be able to do.

CONSTITUTIONAL ISOMERS

Constitutional isomers are compounds that have the same molecular formula and different connectivity. To determine whether two molecules are constitutional isomers, just count the number of each atom in both molecules and see how the atoms are arranged.

OCTANE

Octane is a hydrocarbon and an alkane with the chemical formula C₈H₁₈, and the condensed structural formula CH₃(CH₂)₆CH₃. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers,2,2,4-trimethylpentane (isooctane) is used as one of the standard values in the octane rating scale.

Octane is a component of gasoline (petrol). As with all low molecular weight hydrocarbons, octane is volatile and very flammable

These all are constitutional isomers for octane

2-Methylheptane

​

3-Methylheptane

4-Methylheptane

2,2-Dimethylhexane