What is the structural formula for 4-ethyloctane?

C10H22

Your first step is to understand what that name means. To do that we go right to left and break the name down. FROM THE RIGHT: 4-ethyloctane breaks down into “octane”, “ethyl” and ”4″. Octane means a chain of 8 carbon atoms, ethyl means a chain of 2 carbon atoms which are attached to a molecule and the “4” locates which carbon atom (in the chain of 8) where the “ethyl” (a two carbon chain) is attached.

Here’s what that looks like (ignore the “,”s they are for alignment.)

:
1…… 2 ……3 ……4 …,5…… 6…… 7…….8
CH3-CH2-CH2-CH-CH2-CH2-CH2-CH3 <- 8 carbon chain
……………………… |
…………………… CH2 .
……………………. | . . . 2 carbon chain added
…………………… CH3 . /