Question

Which compounds contain chiral centers? (a) 2-Chloropentane (b) 3-Chloropentane (c) 3-Chloro-l-pentene (d) 1,2-Dichloropropane

Short answer

(a) 2-Chloropentane (b) 3-Chloropentane (c) 3-Chloro-1-pentene (d) 1,2-Dichloropropane

Step-by-step solution

Draw the structures

First, draw the structures of the given compounds by placing Chlorine (Cl) at the designated positions in the name. (a) 2-Chloropentane: H H H | | | H — C — C — Cl — C — H | | H H (b) 3-Chloropentane: H H | | H — C — C — Cl — C — C — H | | | H H H (c) 3-Chloro-1-pentene: H H | | H — C — C == C — Cl — C — H | | H H (d) 1,2-Dichloropropane: H Cl | | H — C — C — Cl — H | | H H

Identify chiral centers

Examine each carbon atom in the molecules and identify any with four different substituents. (a) 2-Chloropentane: H H H | | | H — C — C — Cl — C — H | | H H The carbon with the chlorine atom (in this case, the second carbon) has four different substituents: H, CH3, Cl, and CH2CH3. Therefore, 2-Chloropentane contains a chiral center. (b) 3-Chloropentane: H H | | H — C — C — Cl — C — C — H | | | H H H The carbon with the chlorine atom (in this case, the third carbon) is connected to an H, a Cl, a CH3, and a CH2CH2CH3. Therefore, 3-Chloropentane also contains a chiral center. (c) 3-Chloro-1-pentene: H H | | H — C — C == C — Cl — C — H | | H H The carbon with the chlorine atom (in this case, the third carbon) is connected to an H, a Cl, a CH2==CH2, and a CH3. Therefore, 3-Chloro-1-pentene contains a chiral center. (d) 1,2-Dichloropropane: H Cl | | H — C — C — Cl — H | | H H Neither of the carbons with chlorine atoms has four different substituents. The first carbon has two hydrogens and a chlorine atom, and the second carbon has two chlorine atoms and a hydrogen atom. Therefore, 1,2-Dichloropropane does not contain a chiral center. To summarize, the compounds 2-Chloropentane (a), 3-Chloropentane (b), and 3-Chloro-1-pentene (c) contain chiral centers, while 1,2-Dichloropropane (d) does not.