Question

Identify the chiral molecule from the following:

• A. 2-Bromo-2-methylbutane
• B. 2-Bromo-3-methylbutane
• C. 3-Bromopentane
• D. 2-Bromopropane

Hint:

To locate a chiral carbon quickly, instantly scan the carbon chain for any symmetry. If you see a carbon atom attached to two identical groups (like two methyls or two ethyls), cross it out immediately and keep moving!

Answer 1

The Correct Option is B

Step 1: State the test for chirality.
A molecule is chiral if it has a carbon bonded to four different groups (a stereocentre). The quickest route is to inspect each candidate's key carbon for any repeated group.
Step 2: Check 2-Bromo-2-methylbutane.
The C2 carbon carries Br, ethyl, and two CH$_3$ groups. Two identical methyls means it is not a stereocentre, so this is achiral.
Step 3: Check 2-Bromo-3-methylbutane.
The C2 carbon, written as CH$_3$-C*H(Br)-CH(CH$_3)_2$, carries four different groups: H, Br, CH$_3$, and isopropyl CH(CH$_3)_2$. All four differ, so C2 is a genuine stereocentre.
Step 4: Check 3-Bromopentane.
The C3 carbon carries H, Br, and two ethyl groups. Two identical ethyls make it achiral.
Step 5: Check 2-Bromopropane.
The C2 carbon carries H, Br, and two methyl groups. Two identical methyls make it achiral.
Step 6: Conclude.
Only 2-Bromo-3-methylbutane has a carbon with four distinct groups, so it alone is chiral - option (2).
\[ \boxed{\text{Chiral molecule: 2-Bromo-3-methylbutane (option 2)}} \]