Question

Arrange the compounds in each set in order of decreasing solubility in water. (a) Ethanol, butane, diethyl ether (b) 1 -Hexanol, 1,2-hexanediol, hexane

Short answer

Question: Rank the compounds in each set according to their solubility in water: Set (a): Ethanol (C2H5OH), Butane (C4H10), Diethyl ether (C4H10O) Set (b): 1-Hexanol (C6H13OH), 1,2-Hexanediol (C6H14O2), Hexane (C6H14) Answer: Set (a): Ethanol > Diethyl ether > Butane Set (b): 1,2-Hexanediol > 1-Hexanol > Hexane

Step-by-step solution

Identify the polarities of the compounds

Ethanol( C2H5OH): Polar molecule with hydrogen bonding due to the presence of -OH group. Butane(C4H10): Nonpolar molecule with no hydrogen bonding. Diethyl ether (C4H10O): Polar molecule with no hydrogen bonding because the oxygen atom is bonded to carbon atoms, not hydrogen.

Rank the compounds based on solubility in water

Solubility in water generally follows the order: hydrogen bonding molecules > polar molecules with no hydrogen bonding > nonpolar molecules. Based on this, we have the following order of solubility for set (a): Ethanol > Diethyl ether > Butane #Set (b)#

Identify the polarities of the compounds

1-Hexanol (C6H13OH): Polar molecule with hydrogen bonding due to the presence of -OH group. 1,2-Hexanediol (C6H14O2): Polar molecule with hydrogen bonding due to the presence of two -OH groups. Hexane (C6H14): Nonpolar molecule with no hydrogen bonding.

Rank the compounds based on solubility in water

Solubility in water generally follows the order: hydrogen bonding molecules > polar molecules with no hydrogen bonding > nonpolar molecules. Based on this, we have the following order of solubility for set (b): 1,2-Hexanediol > 1-Hexanol > Hexane

Key concepts

Polarity of Organic Compounds

Understanding the concept of polarity in organic compounds is essential when predicting their interactions with solvents, particularly water. Polarity arises from the distribution of electrical charge across the molecules. In molecules where the atoms have differing electronegativities, such as carbon and oxygen, partial charges develop. The more electronegative atom pulls the shared electrons toward itself more strongly, becoming slightly negative, while the less electronegative atom becomes slightly positive.

Ethanol, as mentioned in the exercise, contains an -OH group, which induces polarity due to the highly electronegative oxygen atom. Diethyl ether is polar as well due to an oxygen atom; however, its geometry makes its overall polarity less than that of ethanol. Butane, in contrast, is nonpolar because its carbon and hydrogen atoms do not create significant polarity in the molecule.

In summary, the polarity of organic compounds is significantly influenced by their molecular structure and the presence of polar bonds, which dictate how they interact with polar solvents like water.

Hydrogen Bonding

Defining Hydrogen Bonds

Hydrogen bonding is a special type of dipole-dipole interaction that occurs when a hydrogen atom is bound to a highly electronegative atom such as nitrogen, oxygen, or fluorine. This situation allows the hydrogen to be attracted to another electronegative atom in a nearby molecule.

Hydrogen Bonds and Solubility

In the context of the exercise, ethanol and 1-hexanol both exhibit hydrogen bonding because of their -OH groups. This capability markedly increases their solubility in water, which itself forms a network of hydrogen bonds. 1,2-Hexanediol has even greater solubility due to having two such groups, allowing it to form more hydrogen bonds. Butane and hexane, without polar -OH groups, cannot form hydrogen bonds and are thus less soluble in water.

The potency of hydrogen bonding in determining solubility is underscored by the significant difference in solubility between molecules that can form hydrogen bonds and those that cannot.

Organic Molecule Solubility

The solubility of organic molecules in water can be considered a dance between polarity and hydrogen bonding. To understand how compounds like those in the exercise dissolve in water, it's crucial to realize that 'like dissolves like.' Polar solvents, such as water, dissolve polar substances, while nonpolar solvents dissolve nonpolar substances.

Solubility is not just about having polar groups but also about the size and proportion of nonpolar parts in a molecule. Even if a molecule has a polar -OH group, if the nonpolar 'tail' is too long, as in the case of hexane relative to 1-hexanol, its solubility in water decreases. This is why 1,2-hexanediol, having two polar -OH groups and a shorter nonpolar region compared to hexane, is more soluble in water.

In summary, when considering organic molecule solubility, one should evaluate the balance between the polar groups that enable hydrogen bonding and the nonpolar regions that can impede solubility in water.