Which of the following compound is not chiral?

• A molecule is chiral if it contains at least one chiral center (carbon bonded to four distinct groups) and lacks an internal plane of symmetry.
• A molecule is achiral if none of its carbons are bonded to four different groups, or if it possesses an internal plane of symmetry.

Structure and Asymmetric Carbon Analysis:

• Option A: 1-Chloropentane

  $$\text{CH}_2\text{Cl}-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3$$

  Let's check the carbons: C1 is bonded to two $$\text{H}$$ atoms; C2, C3, and C4 are bonded to two $$\text{H}$$ atoms each; C5 is bonded to three $$\text{H}$$ atoms. Since no single carbon is attached to four unique groups, the molecule has zero chiral centers.

  Result: Achiral (Not Chiral)




• Option B: 3-Chloro-2-methylpentane

  $$\text{CH}_3-\text{CH(CH}_3)-\text{C}^* \text{HCl}-\text{CH}_2-\text{CH}_3$$

  The C3 carbon ($$\text{C}^*$$) is bonded to four completely different groups: a hydrogen atom ($$-\text{H}$$), a chlorine atom ($$-\text{Cl}$$), an isopropyl group ($$-\text{CH(CH}_3)_2$$), and an ethyl group ($$-\text{CH}_2\text{CH}_3$$).

  Result: Chiral




• Option C: 1-Chloro-2-methylpentane

  $$\text{CH}_2\text{Cl}-\text{C}^* \text{H(CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}_3$$

  The C2 carbon ($$\text{C}^*$$) is bonded to four different groups: a hydrogen atom ($$-\text{H}$$), a methyl group ($$-\text{CH}_3$$), a chloromethyl group ($$-\text{CH}_2\text{Cl}$$), and a propyl group ($$-\text{CH}_2\text{CH}_2\text{CH}_3$$).

  Result: Chiral




• Option D: 2-Chloropentane

  $$\text{CH}_3-\text{C}^* \text{HCl}-\text{CH}_2-\text{CH}_2-\text{CH}_3$$

  The C2 carbon ($$\text{C}^*$$) is bonded to four different groups: a hydrogen atom ($$-\text{H}$$), a chlorine atom ($$-\text{Cl}$$), a methyl group ($$-\text{CH}_3$$), and a propyl group ($$-\text{CH}_2\text{CH}_2\text{CH}_3$$).

  Result: Chiral

Because 1-chloropentane does not contain any asymmetric carbon atoms, it is completely achiral.

Answer: Option A — 1-chloropentane