The number of chiral alcohol(s) with molecular formula C₄H₁₀O is ________.

Solution

Chemistry ma’am · 3 steps

Draw all four butanols, then hunt for one carbon holding four different groups.

1. List the alcohols. C₄H₁₀O fits CₙH₂ₙ₊₂O, so it is saturated with no ring. With a four-carbon skeleton and one -OH, there are exactly four alcohols.
2. Test for chirality. A molecule like this is chiral when one carbon carries four different groups. Two identical groups on that carbon rule it out.

   Alcohol	Structure	Groups on the key carbon	Chiral?
   Butan-1-ol	CH₃CH₂CH₂CH₂OH	C1: H, H, OH, C₃H₇	No
   Butan-2-ol	CH₃CH(OH)CH₂CH₃	C2: H, OH, CH₃, C₂H₅, all different	Yes
   2-Methylpropan-1-ol	(CH₃)₂CHCH₂OH	C2: H, CH₃, CH₃, CH₂OH	No
   2-Methylpropan-2-ol	(CH₃)₃COH	C2: OH, CH₃, CH₃, CH₃	No

3. So. Only butan-2-ol has a stereocentre, so the number of chiral alcohols is 1.

The common slip: 2. Counting the two enantiomers of butan-2-ol separately gives 2, but the question asks for chiral alcohols, so that pair is one compound.

The idea to keep. For chirality counts, first list every structural isomer, then check each carbon for four different groups. Two identical groups, such as two CH₃ or two H, rule that carbon out.

Answer from the NTA final answer key. Solution by PrepWiser.