Indicate whether or not the following molecules are chiral.a) 3,3-dimethylheptaneb) 2,3-dimethylheptanec) 2-methylheptaned) 3-methylheptanee) 4-methylheptane
The Correct Answer and Explanation is :
To determine whether the given molecules are chiral, we need to understand the concept of chirality. A molecule is chiral if it has a non-superimposable mirror image, which typically occurs when a carbon atom has four different substituents (a chiral center).
Let’s analyze each molecule:
a) 3,3-dimethylheptane
Chirality: Not chiral
Explanation: The structure has two methyl groups on the third carbon (3,3-dimethyl), leading to symmetry. Therefore, it has a plane of symmetry, and no chiral centers.
b) 2,3-dimethylheptane
Chirality: Chiral
Explanation: In this molecule, the second and third carbons each have different substituents (C-H, C-C, and C-CH₃ groups). Specifically, the second carbon has a methyl group and a longer carbon chain, and the third carbon also has two different substituents (one is a methyl group, and the other leads to different paths). This leads to non-superimposable mirror images.
c) 2-methylheptane
Chirality: Not chiral
Explanation: In 2-methylheptane, the second carbon (the chiral center) has a methyl group, a hydrogen atom, and two identical carbon chains (the heptane backbone). Thus, it has a plane of symmetry and lacks chirality.
d) 3-methylheptane
Chirality: Not chiral
Explanation: The 3-methylheptane structure has a methyl group on the third carbon. The third carbon has two identical carbon chains attached (from the heptane structure), meaning there is symmetry, making it non-chiral.
e) 4-methylheptane
Chirality: Not chiral
Explanation: Similar to the previous cases, the 4-methylheptane molecule has a methyl group on the fourth carbon. This carbon is attached to two identical carbon chains (the heptane backbone) and thus has a plane of symmetry.
Summary:
- 3,3-dimethylheptane: Not chiral
- 2,3-dimethylheptane: Chiral
- 2-methylheptane: Not chiral
- 3-methylheptane: Not chiral
- 4-methylheptane: Not chiral
In conclusion, only 2,3-dimethylheptane is chiral due to the presence of two different substituents at two carbons. The rest are symmetrical and lack chirality.