Given the molecule $2_{-}\mathrm{chlorobutane}$, how many stereogenic centers does it contain?

• A. $4$
• B. $1$
• C. $0$
• D. $2$

Answer: (B)

Verified step by step guidance

1. Identify the structure of 2-chlorobutane. It is a four-carbon chain (butane) with a chlorine atom attached to the second carbon.
2. Recall that a stereogenic center (chiral center) is a carbon atom bonded to four different groups.
3. Examine each carbon in 2-chlorobutane to see if it has four different substituents. Focus especially on the second carbon where the chlorine is attached.
4. Check the substituents on the second carbon: it is bonded to a chlorine atom, a hydrogen atom, a methyl group (CH3), and an ethyl group (CH2CH3). Since all four groups are different, this carbon is a stereogenic center.
5. Verify the other carbons: the first and fourth carbons are terminal methyl groups (CH3), which are not chiral, and the third carbon is bonded to two hydrogens, so it is not chiral. Therefore, 2-chlorobutane has exactly one stereogenic center.