carboxylic acids are organic compounds that contain what is called the carboxyl group the carboxyl group is a carbon that is double bonded to an oxygen and single bonded to an oxygen which is in turn bonded to a hydrogen which as you can see looks a lot like the carbonyl group and hydroxyl group that are attached together which is where the name comes from any compound that contains this carboxyl group is called a carboxylic acid and gets the suffix and noic acid so we would name this compound here by identifying our longest carbon chain as having two carbons therefore f and with this carboxyl functional group we say it must be a carboxylic acid and is therefore ethanoic acid and now for the first time in organic chemistry we are naming something with two separate words ethanoic and acid with a space between those words the naming conventions remain the same for molecules that include branches here we can see the longest carbon chain is three carbons that being probe and as a result we would call this propanoic acid since it has a carboxyl group attached to it again that is written as two words and then we would see that once again the carboxyl group must always be on carbon number one which means that this methyl branch is on the second carbon and we would call this two methyl propanoic acid