- How many chiral centers are present in each of the following molecular structures?
- Classify each of the molecules in Problem 18.19 as chiral or achiral. 18.24 Classify each of the molecules in Problem 18.20 as chiral or achiral.
- The alkane of lowest molecular mass that has a chiral center has the molecular formula C7H16. Identify the “groups” attached to the chiral center in a molecule of this compound.
- The saturated alcohol of lowest molecular mass that has a chiral center has the molecular formula C4H10O. Identify the “groups” attached to the chiral center in a molecule of this compound.
The Correct Answer and Explanation is :
- Chiral Centers in the Structures:
Without seeing the exact images or structures you’re referring to, I cannot directly count the chiral centers. However, to answer your question on chiral centers in general, a chiral center is a carbon atom bonded to four different substituents. Typically, if a structure has a carbon with two identical substituents or is part of a symmetrical structure, it will not be a chiral center. - Classifying Molecules as Chiral or Achiral:
- Chiral molecules are those that cannot be superimposed on their mirror images. They typically have at least one chiral center and do not possess any symmetry elements, like a plane of symmetry or a center of inversion.
- Achiral molecules are those that can be superimposed on their mirror images. They may have a plane of symmetry or be identical in all directions, which makes them superimposable on their mirror images. For molecules from Problem 18.19 and 18.20, you would need to look at whether the structure has any planes of symmetry or if any of the carbons are bonded to identical groups, indicating achirality.
- Alkane with Lowest Molecular Mass and Chiral Center (C7H16):
The simplest alkane with the formula C7H16 that has a chiral center is 2-methylhexane. The chiral center is the second carbon (C2), which is attached to:
- A methyl group (–CH3),
- An ethyl group (–CH2CH3),
- A propyl group (–CH2CH2CH3),
- A hydrogen atom (H). This carbon is chiral because it is attached to four different groups.
- Saturated Alcohol with Lowest Molecular Mass and Chiral Center (C4H10O):
The simplest alcohol with formula C4H10O that has a chiral center is butan-2-ol. The chiral center is at carbon 2 (C2), which is attached to:
- A hydroxyl group (–OH),
- A methyl group (–CH3),
- An ethyl group (–CH2CH3),
- A hydrogen atom (H). This carbon is chiral because it is bonded to four different groups.
Explanation:
In both examples, the carbon atoms are chiral because each is attached to four different substituents, making them asymmetric. The chiral centers create non-superimposable mirror images, also known as enantiomers, which is the hallmark of chirality. If a carbon has two or more identical substituents or the molecule has a plane of symmetry, it will be classified as achiral.
Chirality is a crucial concept in organic chemistry because it affects the molecule’s interactions with other chiral substances, including its biological activity. For example, the chirality of a drug molecule can influence its pharmacological effects, as different enantiomers can have different effects in the body.