Question

Stearolic acid, \(\mathrm{C}_{18} \mathrm{H}_{32} \mathrm{O}_{2}\), yields stearic acid on catalytic hydrogenation and undergoes oxidative cleavage with ozone to yield nonanoic acid and nonanedioic acid. What is the structure of stearolic acid?

Short answer

Stearolic acid is CH₃(CH₂)₇C≡C(CH₂)₇COOH.

Step-by-step solution

Understanding the Reaction Products

Stearolic acid undergoes oxidative cleavage with ozone to produce nonanoic acid and nonanedioic acid. This indicates that stearolic acid is an unsaturated fatty acid with a specific site where the double or triple bond is located that allows this cleavage.

Analyzing Nonanoic Acid and Nonanedioic Acid

Nonanoic acid is a nine-carbon carboxylic acid: CH₃(CH₂)₇COOH. Nonanedioic acid, also known as azelaic acid, is a dicarboxylic acid with the structure HOOC(CH₂)₇COOH. This suggests that the unsaturation in stearolic acid is between the 9th and 10th carbon atoms.

Determining the Type of Unsaturation

Since stearolic acid becomes stearic acid upon catalytic hydrogenation, it suggests a triple bond is present. This bond is between the 9th and 10th carbon, as oxidative cleavage results in products from splitting at this bond.

Structuring Stearolic Acid

Given the information above, stearolic acid must have an 18-carbon chain with a triple bond between the 9th and 10th carbons, aligning with the oxidation products. This can be represented as: CH₃(CH₂)₇C≡C(CH₂)₇COOH, which reflects the presence of the triple bond and the overall fatty acid structure.

Key concepts

Oxidative Cleavage

Oxidative cleavage is a type of chemical reaction that breaks down unsaturated compounds by cutting through multiple bonds. A common agent for oxidative cleavage is ozone, which is why this process is often called ozonolysis when performed using ozone. This reaction is particularly important in organic chemistry because it helps determine the structure of compounds by breaking them into smaller fragments. The products usually contain carbonyl groups, such as aldehydes, ketones, or carboxylic acids.
In the case of stearolic acid, oxidative cleavage with ozone results in the formation of nonanoic acid and nonanedioic acid. This reveals the exact location of the unsaturation (such as a double or triple bond) within the carbon chain of stearolic acid. By analyzing the resulting fragments, it's possible to deduce that the triple bond in stearolic acid is located between the 9th and 10th carbon atoms. Understanding oxidative cleavage is key to determining the structure of complex organic compounds.

Fatty Acids

Fatty acids are long-chain carboxylic acids that play a pivotal role in biology and chemistry. They can be classified as either saturated, meaning they contain no double or triple bonds, or unsaturated, meaning they have one or more double or triple bonds. The type of bonds they contain influences their chemical properties and reactions.
Stearolic acid is an example of an unsaturated fatty acid with a triple bond. The presence of such multiple bonds affects both its reactivity and its physical properties, such as melting point and stability. Fatty acids like stearolic acid are found in various biological membranes and energy storage molecules.
They can undergo reactions like hydrogenation, where unsaturated fatty acids become saturated, or oxidative cleavage, which helps in determining structure by breaking the molecule down into smaller acid fragments.

Unsaturated Compounds

Unsaturated compounds contain at least one double or triple bond between carbon atoms. These bonds make them more reactive than their saturated counterparts, which only have single carbon-carbon bonds. The reactivity of unsaturated compounds plays a crucial role in many chemical reactions, including hydrogenation, where double or triple bonds are converted to single bonds, and oxidative cleavage.
In stearolic acid, the unsaturation comes in the form of a triple bond between the 9th and 10th carbons. This specific arrangement leads to its reaction with ozone for oxidative cleavage, splitting the molecule into nonanoic acid and nonanedioic acid. Unsaturated compounds are not only important industrially, for processes like polymerization, but also biologically, as they are often key components in cell membranes and signaling molecules.