Step 1: Optical isomerism occurs when a molecule has a chiral center, i.e., a carbon atom attached to four different substituents. For alkenes, this can occur if the double bond leads to non-superimposable mirror images (enantiomers).
Step 2: To check for optical isomerism, we examine each option:
- Option (A)
2−methyl−2−pentene: This molecule has no chiral centers because the two substituents on the second carbon (the methyl groups) are identical, preventing optical isomerism.
- Option (B)
3−methyl−2−pentene: This also lacks a chiral center due to the symmetry of the double bond, so it does not exhibit optical isomerism.
- Option (D)
4−methyl−1−pentene: This compound also does not have a chiral center because the substituents on the carbon atom with the double bond are not different enough to create optical isomerism.
- Option (E)
2−methylpentane: This is an alkane, not an alkene, and lacks a double bond, so it cannot exhibit optical isomerism.
Step 3: Option (C)
3−methyl−1−pentene has a chiral center at the third carbon due to the different substituents attached to it: a hydrogen atom, a methyl group, and two different alkyl groups. This makes the molecule optically active and capable of exhibiting optical isomerism.
Thus, the correct answer is option (C).
Quick Tip: For optical isomerism in alkenes, look for a chiral center formed by a carbon atom attached to four different substituents. This occurs when the alkene is asymmetric and leads to non-superimposable mirror images (enantiomers).