Question

Would you expect alanine (an amino acid) to be more soluble in water or in hexane?

Short answer

Alanine is a polar molecule due to the presence of polar amino and carboxyl groups, despite having a non-polar side chain (methyl group). Based on the principle of "like dissolves like," alanine would be expected to be more soluble in the polar solvent water than in the non-polar solvent hexane.

Step-by-step solution

Determine the structure of alanine

Alanine is an amino acid with the chemical formula C3H7NO2. Its structure consists of an amino group (-NH2), a carboxyl group (-COOH), and a side chain (-CH3, a methyl group) all attached to a central carbon atom (called the alpha carbon).

Analyze the polarity of the functional groups in alanine

The amino group (-NH2) and the carboxyl group (-COOH) are both polar functional groups, with electronegative nitrogen and oxygen atoms forming polar bonds with their attached hydrogen atoms. On the other hand, the methyl group (-CH3) is a non-polar functional group, as carbon and hydrogen have similar electronegativities.

Determine the overall polarity of alanine

Even though alanine has a non-polar side chain (methyl group), the presence of the polar amino and carboxyl groups makes the overall molecule polar.

Compare the polarity of alanine to the polarity of the solvents water and hexane

Water is a polar solvent, which is suitable for dissolving polar molecules like alanine. Hexane, on the other hand, is a non-polar solvent, which would have a harder time dissolving a polar molecule.

Conclude whether alanine is more soluble in water or hexane

Based on the polarity of alanine and the principle of "like dissolves like," alanine would be expected to be more soluble in the polar solvent water than in the non-polar solvent hexane.

Key concepts

Alanine

Alanine is one of the simplest amino acids, integral to life's building blocks. It has the chemical formula \( C_3H_7NO_2 \). This structure comprises an amino group \((-NH_2)\), a carboxyl group \((-COOH)\), and a methyl side chain \((-CH_3)\). All these groups center around a single carbon atom, known as the alpha carbon. This organization gives alanine its characteristic properties.

The carboxyl group \((-COOH)\) and the amino group \((-NH_2)\) provide alanine with acidic and basic behavior, respectively. These groups contribute to alanine's role in forming proteins and participating in various metabolic processes.

Alanine is considered non-essential, meaning our bodies can synthesize it naturally. However, it is vital for the construction of proteins, acting as a fundamental unit in muscle-building and other physiological roles. It also serves as an energy source during prolonged physical activities.

Polarity of molecules

The concept of polarity in molecules is crucial in understanding how substances interact. Polarity is dictated by the difference in electronegativity between atoms in a molecule, which affects how electrons are distributed within it and can lead to the formation of dipoles.

In alanine, while the methyl side chain \((-CH_3)\) is non-polar because carbon and hydrogen have similar electronegativities, several parts of alanine are polar. The carboxyl group \((-COOH)\) is polar due to the highly electronegative oxygen atoms pulling electron density towards them, leading to a partial negative charge. Similarly, the amino group \((-NH_2)\) is polar, as nitrogen attracts more electron density than hydrogen.

Overall molecular polarity is crucial because it influences how molecules behave and interact with their surroundings. Polar molecules, like alanine, can engage in hydrogen bonding and dissolve well in polar solvents, affecting their biological availability and function.

Polar vs non-polar solvents

The concept of "like dissolves like" is fundamental in chemistry, especially when it comes to solubility. This means that substances tend to dissolve best in solvents that have a polarity similar to their own.

Water is a classic polar solvent with a bent molecular structure and partial charges that provide excellent conditions for dissolving polar substances, including alanine. The polar groups in alanine can form hydrogen bonds and interactions with water, facilitating its solubility.

Conversely, hexane is a non-polar solvent composed purely of carbon and hydrogen, forming a straight chain. It is effective for dissolving oils, fats, and other non-polar substances. However, its lack of partial charges and the absence of polar interactions make it unsuitable for dissolving polar molecules like alanine.

• Solubility in water allows for biological processes to take place efficiently as water is abundant in living organisms.
• The interaction between polar molecules and polar solvents like water relies on hydrogen bonding, dipole interactions, and electrostatic attraction.
• Non-polar solvents are used mainly in processes involving non-polar substances such as certain synthetic chemical reactions or oil extractions.