Which compound in each of the following pairs would be more soluble in water? Explain.
c. butanal or hexanal

Verified step by step guidance

1. Step 1: Understand the concept of solubility in water. Water is a polar solvent, meaning it dissolves polar compounds and those capable of hydrogen bonding more effectively than nonpolar compounds.
2. Step 2: Analyze the molecular structure of butanal and hexanal. Both are aldehydes, containing a polar carbonyl group (C=O), which can interact with water molecules through dipole-dipole interactions.
3. Step 3: Consider the impact of the hydrocarbon chain length on solubility. Butanal has a shorter hydrocarbon chain (4 carbons) compared to hexanal (6 carbons). Longer hydrocarbon chains increase the nonpolar character of the molecule, reducing its solubility in water.
4. Step 4: Recall that shorter-chain aldehydes are generally more soluble in water because the polar carbonyl group dominates the molecule's interactions with water, while longer chains reduce this effect.
5. Step 5: Conclude that butanal, with its shorter chain, would be more soluble in water than hexanal due to its higher polarity relative to hexanal.

Key Concepts

Polarity

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between their atoms, tend to dissolve well in water due to hydrogen bonding. In contrast, nonpolar molecules do not interact favorably with water, leading to lower solubility.

Hydrogen Bonding

Hydrogen bonding is a type of attractive interaction that occurs between a hydrogen atom bonded to a highly electronegative atom (like oxygen) and another electronegative atom. This interaction is crucial for the solubility of compounds in water, as molecules that can form hydrogen bonds with water are generally more soluble.

Chain Length and Solubility

The chain length of a molecule affects its solubility in water. Generally, shorter-chain alcohols and aldehydes are more soluble due to their ability to interact with water through hydrogen bonding. As the chain length increases, the hydrophobic (water-repelling) character of the molecule becomes more pronounced, reducing solubility.