Another alcohol nomenclature question

Question

I am confused by the use of these two terms. From the text I am reading, it appears that these two are identical but I don't see how.

1) 2-hydroxy-2-methylbutane

2) 3-methyl-2-butanol

I can see that 3-methyl-2-butanol and 2-methyl-3-butanol are equivalent (flipped), but wouldn't the alkane naming variant of 2-methyl-3-butanol be 2-methyl-3-hydroxy-butane / 2-hydroxy-3-methyl-butane?

Answer 1

Yeah, it seems as though you are right.

2-hydroxy-2-methylbutane would be the same as 2-methyl-2-butanol NOT 3-methyl-2-butanol.

Likewise, 3-methyl-2-butanol would be the same as 2-hydroxy-3-methylbutane.

But be careful when naming alkanes, the group with the highest molecular weight is numbered first so 2-methyl-3-hydroxy-butane cannot exist because this implies methyl has the highest molecular weight. In other words, you can never write 2-methyl-3-hydroxy-butane, it will always be 3-methyl-2-hydroxy-butane, even if you flip it around because you start counting from the carbon closest to the hydroxy group. Alcohols are a little different. The 'ol' at the end of the name implies that the OH group takes precedence but you still begin counting from the carbon closest to the OH (or a compound with a higher molecular weight).

Answer 2

Butane is a linear saturated aliphatic hydrocarbon with 4 carbon atoms.

2-hydroxy-2-methylbutane is butane with the hydrogens on carbon # 2 substituted with OH and CH3 groups.

..........CH3

..........|

CH3 - C - CH2 - CH3.    The "...." are to get the spacing right

..........|

.........OH

2-butanol has the OH group attached to carbon #2. 3-methyl-2-butanol adds a CH3 group on carbon #3.

...............CH3

...............|

CH3 - C - CH2 - CH3.    

..........|

.........OH  

As you can see, the two molecules are NOT the same.  OK?

Answer 3

I'm sure they are not the same. Using Me for the methyl radical and ignoring most of the H atoms (makes it clearer):

1) is Me-C(OH)Me-C-Me

2) is Me-C(OH)-CMe-Me

Answer 4

yes, you are right and  the author of the text is incorrect. the convention for naming was invented to stop ambiguous names. they are the same molecules but the author has taken both ends of the molecule as 1 so the methyl group and hydroxy are on adjacent carbons but the author has denoted them both as 2 not two and three. the group that dictates the functionality is usually given the lowest number. i.e a carboxylic carbon is always number one and once you have denoted one side as 1 then you count away from that carbon but your alternative is correct and wouldn't be marked wrong.