Draw the structural formula of an alkane that has eight carbons with only primary hydrogens.

To draw the structural formula of an alkane with eight carbons that contains only primary hydrogens, we first need to understand what an alkane is and what primary hydrogens mean. Alkanes are saturated hydrocarbons, which means they consist solely of carbon (C) and hydrogen (H) atoms, with single bonds between the carbon atoms. The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms.

Understanding Primary Hydrogens

Primary hydrogens are those attached to a primary carbon atom, which is a carbon atom bonded to only one other carbon atom. In a straight-chain alkane, the terminal carbon atoms are primary, while the internal ones can be secondary or tertiary depending on how many other carbon atoms they are bonded to.

Constructing the Alkane

For an alkane with eight carbon atoms, we can use the formula C8H18. To ensure that all hydrogens are primary, we need to arrange the carbon atoms in a way that maximizes the number of terminal carbon atoms. The best way to achieve this is by using a straight-chain structure, which is known as octane.

Drawing the Structure

The structural formula of octane can be represented as follows:

• Start with a straight line of eight carbon atoms: C-C-C-C-C-C-C-C
• Each terminal carbon (the first and the last) will have three hydrogens attached, while the internal carbons will have two hydrogens each.

So, the complete structural formula looks like this:

   H   H   H   H   H   H   H   H
   |   |   |   |   |   |   |   |
H--C---C---C---C---C---C---C---C--H
   |   |   |   |   |   |   |   |
   H   H   H   H   H   H   H   H

Visualizing the Structure

In this representation, you can see that the two terminal carbon atoms (the first and the last) each have three hydrogens, while the six internal carbon atoms each have two hydrogens. This arrangement ensures that all hydrogens attached to the carbon atoms are primary, as they are all connected to terminal carbon atoms.

Conclusion

In summary, the structural formula of octane (C8H18) illustrates how we can have an alkane with eight carbon atoms and only primary hydrogens by arranging the carbon atoms in a straight chain. This structure is not only simple but also a fundamental example of how alkanes are structured in organic chemistry.