Question

Which of the following is optically active? (1) Alanine (2) 2-Butanol (3) Lactic acid (4) All

Short answer

All are optically active.

Step-by-step solution

Identify the structure of each compound

Draw or visualize the molecular structures of Alanine, 2-Butanol, Lactic acid and inspect for any chiral centers.

Analyze Alanine

Alanine is an amino acid with the structure CH3-CH(NH2)-COOH. It has a chiral center at the carbon atom attached to NH2, CH3, H, and COOH groups, making it optically active.

Analyze 2-Butanol

2-Butanol has the structure CH3-CHOH-CH2-CH3. It contains a chiral center at the second carbon (attached to OH, H, CH3, and CH2CH3 groups), making it optically active.

Analyze Lactic Acid

Lactic Acid (2-Hydroxypropanoic acid) has the structure CH3-CHOH-COOH. It has a chiral center at the second carbon atom (attached to OH, H, CH3, and COOH groups), making it optically active.

Combine findings

All three compounds, Alanine, 2-Butanol, and Lactic acid, have chiral centers and are optically active.

Key concepts

Chiral Centers

Chiral centers play a crucial role in the optical activity of molecules. A chiral center is a carbon atom that is attached to four different groups. This unique arrangement leads to non-superimposable mirror images, known as enantiomers. Each enantiomer can rotate plane-polarized light either to the left (levorotatory) or to the right (dextrorotatory). Identifying chiral centers helps in determining if a molecule is optically active.
For example:

• Alanine, with its structure CH3-CH(NH2)-COOH, has a chiral center at the carbon attached to NH2, CH3, H, and COOH.
• 2-Butanol, with the structure CH3-CHOH-CH2-CH3, contains a chiral center at the second carbon atom.
• Lactic acid (CH3-CHOH-COOH) has a chiral center at the second carbon, bonded to OH, H, CH3, and COOH.

Each of these compounds is therefore optically active due to the presence of a chiral center.

Amino Acids

Amino acids are the building blocks of proteins and have the general formula NH2-CHR-COOH. Each amino acid can have different side chains (R groups), leading to its unique properties. Many amino acids have chiral centers, which contribute to their optical activity. For instance, Alanine has a chiral center at the carbon atom next to the amino group (NH2), making it optically active. The presence of chiral centers in amino acids is essential for protein structure and function, as they lead to the formation of specific 3D configurations necessary for biological activity.

Organic Compounds

Organic compounds are primarily made of carbon and hydrogen atoms and can also include other elements like oxygen, nitrogen, sulfur, and halogens. They can range from simple molecules like methane (CH4) to complex macromolecules like proteins and DNA. Optical activity in organic compounds generally arises from chiral centers within the molecules. For example, in the organic compounds given:

• Alanine, an amino acid, is optically active due to its chiral center.
• 2-Butanol, an alcohol, is optically active because of its chiral center at the second carbon.
• Lactic acid, a carboxylic acid, is also optically active due to its chiral center at the second carbon.

Understanding the structure of organic compounds helps in predicting their optical activity and their role in various chemical reactions and biological systems.

Molecular Structure Analysis

Molecular structure analysis is essential for understanding the properties and behavior of molecules. It involves examining the spatial arrangement of atoms within a molecule. When analyzing a molecule's structure to determine its optical activity, we look for chiral centers. Tools like molecular models, chirality tests, and spectroscopy are used for this purpose.
By analyzing the following structures:

• Alanine (CH3-CH(NH2)-COOH)
• 2-Butanol (CH3-CHOH-CH2-CH3)
• Lactic acid (CH3-CHOH-COOH)

We can confirm their optical activity based on their chiral centers. This analysis is crucial for applications in fields like medicinal chemistry, where the optical activity of compounds can affect drug efficacy and safety.