Naming

[Nayeon Kang 2M]

For the organic molecules at pg 92, why can't we say it's 5-Ethyl-3-Methyl-Heptane?

[Ana Ordonez 1G]

We can't name it 5-ethnyl-3-methyl-heptance because when numbering the carbons in the longest hydrocarbon chain, the carbons have the same numbers going from right to left and left to right. In this case we look at the names of the substituent and whichever comes first alphabetically, that is the one that will get the lowest number. Ethyl comes first so we will number the carbons from left to right making methyl on 5.