C5 alkanols

All of these molecules have molecular formula C5H12O. Their names, and boiling points (oC) are:

....1. 1-pentanol (138.0).............. 2. 2-pentanol (119.0) .................... 3. 3-pentanol (115.6)

....4. 2-methyl-1-butanol (128.0).. 5. 3-methyl-1-butanol (131.1) ........ 6. 2-methyl-2-butanol (102.4)

....7. 3-methyl-2-butanol (112.9).. 8. 2,2-dimethyl-1-propanol (113).....9. 1,1-dimethyl-1-propanol ?

We have not given the boiling point of the last compound in this list because this compound is not to be found in chemistry reference books. Why is this?

This is not a separate isomer. It is not a propanol; since the longest carbon-chain has four carbon atoms, it is a butanol. In fact it is the same as number 6, ....2-methyl-2-butanol.