Problem 103 - Chemistry An Atoms First Approach

Question

Which of the noncyclic isomers of bromochloropropene are optically active?

Step-by-Step Solution

Answer

The noncyclic isomers of bromochloropropene that are optically active are 1-Bromo-2-chloropropene, 2-Bromo-1-chloropropene, and 3-Bromo-2-chloropropene, as they each have at least one chiral center.

Step 1: Identify all possible noncyclic isomers of bromochloropropene

Let's find all the possible noncyclic isomers for bromochloropropene (C3H3BrCl). Bromochloropropene has three carbon atoms, one bromine atom, and one chlorine atom. The isomers can have different placements of the bromine and chlorine atoms in the carbon chain. There are four possible isomers: 1. 1-Bromo-1-chloropropene: Br and Cl are both attached to the first carbon atom. 2. 1-Bromo-2-chloropropene: Br is attached to the first carbon atom, and Cl is attached to the second carbon atom. 3. 2-Bromo-1-chloropropene: Br is attached to the second carbon atom, and Cl is attached to the first carbon atom. 4. 3-Bromo-2-chloropropene: Br is attached to the third carbon atom, and Cl is attached to the second carbon atom.

Step 2: Understand the concept of optical activity

Optical activity is the ability of a molecule to rotate plane-polarized light. A molecule is optically active if it has at least one chiral center. A chiral center is an atom that has four different groups attached to it and is non-superimposable on its mirror image. In the case of the isomers of bromochloropropene, we need to identify which isomers have chiral centers.

Step 3: Identify isomers with chiral centers

Now, let's examine each isomer to see if it has a chiral center: 1. 1-Bromo-1-chloropropene: The first carbon atom has two different groups (Br and Cl) attached, but it also has two identical hydrogen atoms. Hence, it is not a chiral center. 2. 1-Bromo-2-chloropropene: The second carbon atom has four different groups (Br, Cl, H, and a methyl group) attached to it. This makes it a chiral center. 3. 2-Bromo-1-chloropropene: The first carbon atom has four different groups (Br, Cl, H, and a methyl group) attached to it. This makes it a chiral center. 4. 3-Bromo-2-chloropropene: The second carbon atom has four different groups (Br, Cl, H, and a methyl group) attached to it. This makes it a chiral center.

Step 4: Determine the optically active isomers

Since 1-Bromo-2-chloropropene, 2-Bromo-1-chloropropene, and 3-Bromo-2-chloropropene have at least one chiral center, they are optically active. In conclusion, the noncyclic isomers of bromochloropropene that are optically active are 1-Bromo-2-chloropropene, 2-Bromo-1-chloropropene, and 3-Bromo-2-chloropropene.