4-nonanone
Explanation: there is a functional group in the compound CH3CH2CH2CH2CH2COCH2CH2CH3 which is a ketone; So for naming a ketone we must first mention the name of the prefix that is correspond then add the suffix ''one''. And why I putted a ''4'' before the name is because we must indicate where this functional group is located, for doing that we have to start counting where the functional group is the closet to the end of the compound so when looking we should start to count on the right side. this is how I get 4-nonanone
