Question

A compound with molecular formula \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{4}\) on acylation with acetic anhydride gives a compound with molecular formula \(\mathrm{C}_{12} \mathrm{H}_{18} \mathrm{O}_{8}\). How many hydroxyl groups are present in the compound? (a) 2 (b) 3 (c) 4 (d) 5

Short answer

The compound has 4 hydroxyl groups, so the answer is (c) 4.

Step-by-step solution

Understanding Acylation Process

Acylation is a chemical reaction where an acyl group is introduced into a molecule. In this case, acylation with acetic anhydride typically converts hydroxyl groups (-OH) in a compound into ester groups by replacing the hydrogen atom in the hydroxyl group with an acetyl group.

Analyze the Change in Molecular Formula

The initial compound has a molecular formula of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{4}\) and after acylation, the new molecular formula is \(\mathrm{C}_{12} \mathrm{H}_{18} \mathrm{O}_{8}\). The change indicates that each hydroxyl group has been replaced by an acetyl group (\(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}\)).

Calculate Number of Acetyl Groups Added

Determine how many acetyl groups were added by comparing the carbon, hydrogen, and oxygen changes:- 8 new carbon atoms are present (from \(\mathrm{C}_4\) to \(\mathrm{C}_{12}\)), suggesting 4 acetyl groups each contributing 2 carbons.- Similarly, 8 new hydrogen atoms (from \(\mathrm{H}_{10}\) to \(\mathrm{H}_{18}\)) and 4 new oxygen atoms (from \(\mathrm{O}_4\) to \(\mathrm{O}_8\)) confirm adding 4 acetyl groups.

Conclusion on Number of Hydroxyl Groups

Each added acetyl group corresponds to an original hydroxyl group. Since 4 acetyl groups were added, the original compound must have had 4 hydroxyl groups.

Key concepts

Understanding Acylation Reaction

Acylation is an essential reaction in organic chemistry where an acyl group, typically (-CO-), is introduced into a molecule. This process is important for modifying molecules to create more complex compounds. In the context provided, acylation is performed using acetic anhydride. Here's how it works:

• The acylation reaction targets hydroxyl groups (-OH) in a compound.
• In this reaction, each hydroxyl group's hydrogen is replaced by an acetyl group, which comes from the acetic anhydride.
• This transformation results in the formation of esters, as the hydroxyl groups are converted to acetyl groups.

This reaction is highly efficient and widely used both in laboratory and industrial settings to synthesize esters. Due to the reliable reactivity of acyl groups, it's a preferred method for modifying molecular structures, allowing chemists to create diverse and functional new compounds.

Molecular Formula Analysis Demystified

Analyzing molecular formulas effectively is crucial in understanding chemical reactions and the structure of compounds. Let's delve deeper with an example:

• Initially, we have a compound: \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{4}\).
• After undergoing acylation, it transforms into: \(\mathrm{C}_{12} \mathrm{H}_{18} \mathrm{O}_{8}\).
• By comparing the two formulas, we can track the changes in atoms.
• The carbon atoms increase by 8, hydrogen by 8, and oxygen by 4.
• These changes suggest the introduction of 4 acetyl groups because each group adds two carbons, three hydrogens, and one oxygen.

An in-depth formula analysis helps identify how many functional groups were altered during the reaction. In this case, the changes are consistent with converting 4 hydroxyl groups into ester bonds through acylation. This ensures the accuracy of our conclusions and confirms the presence of these chemical groups in the new compound.

Esterification Process Unlocked

Esterification is a specific reaction where esters are formed. In this case, acylation with acetic anhydride creates esters from hydroxyl groups. Here's what you need to know to understand this transformation:

• Hydroxyl groups are critical starting points. The -OH group in alcohols allows for reaction with acetic anhydride.
• Acetic anhydride performs the acylation, where the acetyl group (CH3CO) attaches to the oxygen of the hydroxyl group, forming an ester bond.
• In our exercise, this process converts the compound \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{4}\) into \(\mathrm{C}_{12} \mathrm{H}_{18} \mathrm{O}_{8}\), indicating the formation of four esters.

This process is fundamental for the synthesis of many organic compounds and is used extensively in both academia and industry. Understanding esterification allows one to predict and manipulate changes in molecular structures, crucial for the development of synthetic processes and new materials.