Pentane has a C5H12 formula, if we take one H and substitute it with an OH (hydroxyl group), we will end up with C5H11OH, and that has a few isomers, which are different structures for the same chemical formula.
C5H11OH can be: Pentan-1-ol; Pentan-2-ol; Pentan-3-ol; Neo-pentanol; 2-methylbutan-1-ol; Iso-pentanol, and more.