Which compounds contain chiral centers?
(a) 2-Chloropentane
(b) 3-Chloropentane
(c) 3-Chloro-1-pentene
(d) 1,2-Dichloropropane
A chiral center is a carbon that is attached to 4 different groups.
We should start by drawing out molecules, and adding the necessary number of hydrogens to each carbon. Remember a carbon wants to always have 4 bonds. Therefore, if we see a carbon with 2 bonds, we attach 2 more hydrogens and so forth. We can always eliminate carbons that have 2 or 3 hydrogens since they do not contain 4 different groups.
In 2-chloropentane, carbon 2 is attached to chlorine, hydrogen, one carbon on the left and 3 carbons on the right. Therefore, carbon 2 is a chiral center. Choice A contains a chiral center
In 3-Chloropentane, carbon 3 is attached to chlorine, hydrogen, 2 carbons on the left and 2 carbons on the right. Therefore, 3-chloropentane, choice B, does not have a chiral center.
3-Chloro-1-pentene does have a chiral center on carbon 3, since that carbon is attached to a chlorine, hydrogen, 2 carbons with a double bond on the left and two carbons without a double bond on the right.
Finally, 1,2-Dichloropropane also has a chiral center on carbon 2, since this carbon is attached to a chlorine, hydrogen, one carbon with a chlorine and another carbon without a chlorine.
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