Question

What are the products, and their relative ratios, resulting from the ozonolysis of \(\beta\) -carotene? (Assume reductive workup.)

Short answer

After performing ozonolysis followed by reductive workup on β-carotene, the products obtained are: 2 moles of 1,4-pentadienal (aldehyde), 7 moles of acetone (ketone), and 2 moles of isoprenoid-derived aldehyde. The ratio of 1,4-pentadienal to acetone is 1:3.5, and the ratio of 1,4-pentadienal to isoprenoid-derived aldehyde is 1:1.

Step-by-step solution

Identify the structure of β-carotene

To determine the products and their relative ratios, we first need to analyze the structure of β-carotene. β-carotene is an organic compound with a molecular formula of C40H56 and an unsaturated hydrocarbon, which means it has carbon-carbon double bonds in its structure. Its structure consists of a long conjugated chain with alternating single and double bonds, terminated by isoprenoid groups on both ends.

Understand the process of ozonolysis

Ozonolysis is a chemical reaction where ozone (O3) breaks the carbon-carbon double bonds in unsaturated hydrocarbons, such as β-carotene, to generate two new molecules. It is important to note that there are two types of workups for ozonolysis: reductive and oxidative. In this exercise, we are assuming a reductive workup by adding a reducing agent like dimethyl sulfide (DMS) after ozonolysis.

Perform ozonolysis on β-carotene

In the case of β-carotene, the central conjugated chain has a total of 11 carbon-carbon double bonds. All these double bonds will undergo ozonolysis, generating two new molecules (carbonyl-containing molecules) for each double bond. After the ozonolysis process, reductive workup will be performed to convert any intermediate ozonides into carbonyls.

Identify the products and their relative ratios

After performing ozonolysis followed by reductive workup on β-carotene, the products obtained can be divided into two groups: 1. Aldehydes: At both the end of the β-carotene molecule, aldehyde groups are formed. 2. Ketones: The remaining double bonds within the chain will be cleaved, giving rise to ketone groups. Overall, from the ozonolysis of β-carotene, we will obtain the following products and their relative ratios: - 2 moles of 1,4-pentadienal (aldehyde): end groups for each β-carotene molecule. - 7 moles of acetone (ketone): from internal double bond cleavage. - 2 moles of isoprenoid-derived aldehyde Thus, the ratio of 1,4-pentadienal to acetone is 1:3.5 whereas the ratio of 1,4-pentadienal to isoprenoid-derived aldehyde is 1:1.

Key concepts

Organic Reaction Mechanisms

Organic reaction mechanisms are like the scripts that direct the dance of molecules during a chemical reaction. Each step in these mechanisms involves specific actions, such as the making and breaking of bonds. This is crucial for understanding how starting materials transform into products. In the context of β-carotene's ozonolysis, we focus on the mechanism where ozone attacks the carbon-carbon double bonds. Generally, ozonolysis involves the formation of an ozonide intermediate, which can then be worked up to form carbonyl compounds. The mechanism specifically depends on whether a reductive or oxidative workup is used, which will determine the final nature of the products. Understanding mechanisms helps predict the outcome of reactions and the formation of specific bonds. Grasping the basics of these processes is essential for mastering organic chemistry.

Carbon-Carbon Double Bonds

Carbon-carbon double bonds are a critical feature in organic compounds, acting as sites of reactivity. During ozonolysis, these double bonds get cleaved to form more oxidized products. In β-carotene, there are 11 carbon-carbon double bonds within its structure that are susceptible to attack by ozone. These double bonds are part of a conjugated system, providing the characteristic color of β-carotene and serving as a structural backbone. During ozonolysis, each double bond breaks in the presence of ozone, producing carbonyl compounds such as aldehydes and ketones. The reactivity of double bonds highlights their importance in reactivity and functionality in organic molecules. Understanding how these bonds work and react is foundational when studying organic reactions.

Reductive Workup

Reductive workup is an essential step in some ozonolysis procedures, designed to convert unstable ozonides into more stable carbonyl compounds like aldehydes and ketones. This step involves the addition of a reducing agent which helps in preventing further oxidation of carbonyl products. In the reductive workup of β-carotene, dimethyl sulfide (DMS) is often used as a reducing agent. It stabilizes the products by preventing them from converting into acids or other more oxidized forms. This process ensures that the products of ozonolysis remain as non-acidic carbonyl compounds, influencing both their structure and functionality. The role of reductive workup is to finalize the transformation started by ozonolysis and to secure products that can have significant synthetic applications.

Chemical Products and Ratios

Chemical products and their ratios from a reaction tell us not only what was formed but also give insights into the efficiency and selectivity of the reaction. When β-carotene undergoes ozonolysis, it transforms into specific products based on its original structure and the reaction conditions. For β-carotene treated with a reductive workup, the products include:

• 2 moles of 1,4-pentadienal, arising from the terminal sections of the molecule.
• 7 moles of acetone, produced from the internal double bonds.
• 2 moles of isoprenoid-derived aldehyde.

The relative ratio of 1,4-pentadienal to acetone is 1:3.5, illustrating that for every mole of 1,4-pentadienal, there are 3.5 moles of acetone produced. Additionally, the ratio of 1,4-pentadienal to isoprenoid-derived aldehyde is 1:1. These ratios are crucial for understanding the composition and potential applications of the reaction products. They help chemists optimize reactions and design new syntheses.