Problem 81 - Chemistry: The Central Science

Question

Draw the condensed structural formulas for two molecules with the formula \(\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}\).

Step-by-Step Solution

Answer

Two possible molecules with the formula \(\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}\) are: 1. Propenal (an aldehyde): \(CH_2=CH-CHO\) 2. 2-Propen-1-ol (an allyl alcohol): \(CH_2=C(CH_3)-OH\)

Step 1: Identify possible functional groups and molecular skeletons

Since the molecular formula is \(\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}\), we should check for common functional groups like the carbonyl group (-C=O), alcohol group (-OH) or alkene (-C=C-). In addition, we should also consider different molecular skeletons, like a linear or branched carbon chain.

Step 2: Generate isomers

Let's form two different molecules by adjusting the positions of the functional groups and molecular skeletons. Molecule 1: Since we have 3 carbons and 1 oxygen, we can make a linear molecule with an aldehyde functional group. In this case, we will have a double bond (C=O) and the other carbons forming singly bonded (C-C) chains. Molecule 2: For the branched molecule, there are two carbons in the main chain, while the other carbon is attached to the second carbon, creating an alcohol group (-OH) attached to the last carbon.

Step 3: Draw the condensed structural formulas

Now that we have outlined the structures of two different molecules that have the formula \(\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}\), let's draw their condensed structural formulas. Molecule 1: \(CH_2=CH-CHO\) (propenal, an aldehyde) Molecule 2: \(CH_2=C(CH_3)-OH\) (2-propen-1-ol, an allyl alcohol)

Key Concepts

Condensed Structural Formula

In organic chemistry, the condensed structural formula is a streamlined way to represent the arrangement of atoms in a molecule. It shows which atoms are connected to which, but unlike the full structural formula, it does not explicitly display every single bond. It conveniently lists atoms close together to indicate bonding. For example, in the exercise, the condensed structural formula of propenal is given as \(CH_2=CH-CHO\). This indicates:

• Carbons are forming a carbon chain.
• Double bonds are written with '=' between atoms.
• The placement of \(CHO\) signifies it is bonded to a carbon that is double-bonded within the chain.

This method allows for an easy and quick representation of organic molecules without drawing out each bond explicitly. But it's important to remember that it only suggests atom connectivity and we often need the full displayed structure for a complete understanding.

Isomerism

Isomerism is a fascinating concept in organic chemistry, where molecules with the same molecular formula have different arrangements of atoms or bonds. These different forms are called isomers. In the exercise, the formula \(C_3H_4O\) was illustrated to produce two such isomers:

• Propenal with a linear aldehyde structure: \(CH_2=CH-CHO\)
• 2-propen-1-ol with a branched alcohol structure: \(CH_2=C(CH_3)-OH\)

The difference between them lies in their connectivity and placement of functional groups while having the same atoms and numbers. Isomerism highlights chemical diversity in specific formulas, as these varied structures can lead to dramatically different chemical properties and functions.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They define many of the properties and reactions of organic compounds. For molecules with the formula \(C_3H_4O\), they exhibit different functional groups which drastically alter their chemical behavior:

• Aldehyde group (-CHO) in propenal, which gives it typical aldehyde properties such as participation in nucleophilic addition reactions.
• Alcohol group (-OH) in 2-propen-1-ol, which allows it to engage in reactions typical of alcohols, like dehydration or hydrogen bonding.

These functional groups not only determine molecular reactivity but also often define the categories into which organic compounds fall, making them a central theme in the study of organic chemistry.