Problem 104 - Chemistry The Molecular Science

Question

Two different compounds each have the formula \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}\). Each contains a \(\mathrm{C}=\mathrm{O}\) group. Write the Lewis structure of each compound and identify the functional group or functional groups in each one

Step-by-Step Solution

Answer

The compounds are acetic acid (carboxylic acid) and methyl formate (ester).

Step 1: Understand the Molecular Formula

The molecular formula is \( \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2} \), indicating there are 2 carbon atoms, 4 hydrogen atoms, and 2 oxygen atoms, and each compound includes a \( \mathrm{C} = \mathrm{O} \) group. This molecular formula suggests a carboxylic acid or an ester.

Step 2: Draw the Lewis Structure for Acetic Acid

Acetic acid has the formula \( \mathrm{CH}_3\mathrm{COOH} \). The central carbon (C) is bonded to a hydroxyl group (\( \mathrm{OH} \)) and a \( \mathrm{C} = \mathrm{O} \) group, forming a carboxylic acid functional group. The Lewis structure can be represented as:\[\begin{array}{c} H \hspace{1mm } \vdash \hspace{1mm}C \dash H ewline | \hspace{6mm} | ewlineO \dash C \dash H ewline| \ O\end{array}\]

Step 3: Draw the Lewis Structure for Methyl Formate

Methyl formate is an ester with the formula \( \mathrm{HCOOCH}_3 \). It consists of a \( \mathrm{C=O} \) group bonded to another oxygen, which in turn is bonded to an \( \mathrm{CH}_3 \) group. The Lewis structure is:\[\begin{array}{c} H \vdash C \dash O \dash C \dash H \dash H ewline | \ O\end{array}\]

Step 4: Identify Functional Groups

In the acetic acid structure, the functional group is a carboxylic acid (\( \mathrm{COOH} \)). In the methyl formate structure, the functional group is an ester (RCOOR').

Key Concepts

Molecular Formula

A molecular formula tells us how many of each type of atom are present in a molecule. For instance, the molecular formula \( \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2} \) indicates that a molecule contains two carbon atoms, four hydrogen atoms, and two oxygen atoms. It can represent more than one compound. This is because different compounds can have the same number and type of atoms arranged in different ways. Such compounds are known as isomers.
In the context of our exercise, \( \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2} \) represents acetic acid and methyl formate. Both have distinct structures but contain the same type and number of atoms. The presence of the \( \mathrm{C=O} \) group in both is a key hint that our compounds may involve one or more specific functional groups like carboxylic acids or esters.

Carboxylic Acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group \( \mathrm{(-COOH)} \). This functional group is made up of a carbonyl \( \mathrm{C=O} \) and a hydroxyl group \( \mathrm{O-H} \).
The simplest and most well-known carboxylic acid is acetic acid, which is a component of vinegar. Its Lewis structure, which shows the arrangement of electrons, can help visualize its molecular configuration. In acetic acid's structure, one hydrogen is connected to a carbon atom. This carbon is then linked to a carbonyl group \( \mathrm{C=O} \) and a hydroxyl group \( \mathrm{OH} \), forming the carboxyl group. The presence of the carboxylic acid group influences the chemical properties of the molecule, such as its ability to donate a proton (H\(^+\)), providing its acidic character.

Ester

Esters are a class of organic compounds formed from an alcohol and a carboxylic acid through a reaction known as esterification. They have a distinctive \( \mathrm{RCOOR'} \) functional group, where \( \mathrm{R} \) and \( \mathrm{R'} \) can be either hydrocarbon chains or other organic groups.
In the exercise, methyl formate serves as an example of an ester. The molecule includes a \( \mathrm{C=O} \) group bonded to an oxygen atom, which is further connected to a methyl group \( \mathrm{CH}_3 \). This configuration is what gives esters their unique properties, such as their often pleasant, fruity odors. As illustrated in the Lewis structure, esters have a specific electronic arrangement that affects their reactivity and interaction with other molecules.

Functional Groups

Functional groups are specific groups of atoms within molecules that have their own characteristic properties. They help define the chemistry of a molecule. Identifying functional groups is key to understanding a molecule's reactivity and interaction.
In organic chemistry, functional groups like carboxylic acids \( \mathrm{(-COOH)} \) and esters \( \mathrm{(RCOOR')} \) serve as the cornerstone for predicting and explaining chemical behavior. In acetic acid, the carboxylic acid group endows it with acidic properties, while in methyl formate, the ester group alters its reactivity and gives it distinct physical properties like smell. Recognizing these groups in the Lewis structures gives insight into potential chemical reactions, such as acid-base reactions in carboxylic acids or the formation of esters from alcohols and acids.