Ethanol and Butanoic acid are used to form the ester is ethyl butanoate AND waterFirst part of the molecule is the carboxylic acid group and the second comes from the alchohol, These two bond to form an ester linkage.How to remember this: If the group next to the COO was a Hydrogen, then you get the starting carboxylic acid (remember the C=O belongs to the acid)4 carbons = butanoic acid , 2 carbons = ethanolnote that the alcohol is the first part of the name (-yl) and the acid is the -oate part of the name of the ester. This is the opposite way of the structure of the compound.Water is formed because Butanoic acid gives up its hydroxyl group and the alcohol loses a Hydrogen cation. Therefore, The hydroxyl group OH- and H+ join to form water.