Problem 69 - Chemistry Matter and Change

Question

Communicate Write structural formulas for all structural isomers of molecules having the following formulas. Name each isomer. a. \(C_{3} \mathrm{H}_{8} \mathrm{O} \quad\) b. \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

The two structural isomers of C₃H₈O are Propan-2-ol: \( \mathrm{H}_{3} \mathrm{C} - \mathrm{CH} (\mathrm{OH}) - \mathrm{CH}_{3} \) and Methoxyethane: \( \mathrm{H}_{3} \mathrm{C} - \mathrm{CH}_{2} - \mathrm{O} - \mathrm{CH}_{3} \). The structural isomers of C₂H₄Cl₂ are 1,1-Dichloroethene: \( \mathrm{H}_{2} \mathrm{C} (\mathrm{Cl})_{2} - \mathrm{CH}_{2} \), cis-1,2-Dichloroethene and trans-1,2-Dichloroethene, which both have the same structural formula: \( \mathrm{H}_{2} \mathrm{C} \mathrm{Cl} - \mathrm{CH} (\mathrm{Cl}) \mathrm{H} \), and 2,2-Dichloroethene: \( \mathrm{H}_{2} \mathrm{C} - \mathrm{CH} (\mathrm{Cl})_{2} \).

Step 1: a. Structural isomers of C3H8O

To find the isomers of C3H8O, we can start by considering different possibilities of carbon chains, and where the oxygen atom can be positioned. Possibility 1: A single carbon chain with three carbons is called propane, which has the molecular formula C3H8. Since we need to add an oxygen atom, we have two possible locations for this oxygen atom: 1. Substituting one of the hydrogen atoms in the middle carbon (C2) with the oxygen atom. 2. Adding the oxygen atom in between the second and the third carbon atoms. Possibility 2: A carbon chain with two carbons and one methyl group attached. Here, the main carbon chain would be called ethane, with the molecular formula C2H6. Since we need to add an oxygen atom, we can replace one of the hydrogen atoms in the ethane molecule with the oxygen atom, which can then form a bond with the methyl group. From these possibilities, the two possible structural isomers are: 1. Iso-propyl alcohol (Propan-2-ol) \( \mathrm{H}_{3} \mathrm{C} - \mathrm{CH} (\mathrm{OH}) - \mathrm{CH}_{3} \) 2. Ethyl methyl ether (Methoxyethane) \( \mathrm{H}_{3} \mathrm{C} - \mathrm{CH}_{2} - \mathrm{O} - \mathrm{CH}_{3} \)

Step 2: b. Structural isomers of C2H4Cl2

To find the isomers of C2H4Cl2, we will consider a single carbon chain with two carbons and four hydrogen atoms called ethene. We need to add two chlorine atoms in place of two hydrogen atoms. There are three possible locations. 1. Substituting both hydrogen atoms of the first carbon atom with chlorine atoms. 2. Substituting one hydrogen atom each from the first and second carbon atoms with chlorine atoms. 3. Substituting both hydrogen atoms of the second carbon atom with chlorine atoms. This gives us three possible structural isomers: 1. 1,1-Dichloroethene \( \mathrm{H}_{2} \mathrm{C} (\mathrm{Cl})_{2} - \mathrm{CH}_{2} \) 2. 1,2-Dichloroethene (cis or trans) cis-1,2-Dichloroethene: \( \mathrm{H}_{2} \mathrm{C} \mathrm{Cl} - \mathrm{CH} (\mathrm{Cl}) \mathrm{H} \) trans-1,2-Dichloroethene: \( \mathrm{H}_{2} \mathrm{C} \mathrm{Cl} - \mathrm{CH} (\mathrm{Cl}) \mathrm{H} \) 3. 2,2-Dichloroethene \( \mathrm{H}_{2} \mathrm{C} - \mathrm{CH} (\mathrm{Cl})_{2} \)

Key Concepts

Organic Chemistry: The Science of Carbon Compounds

At the heart of organic chemistry is the study of carbon-based compounds. This fascinating branch of chemistry delves into the structures, properties, and reactions of molecules that contain carbon atoms. Carbon's ability to form strong covalent bonds with a variety of other elements, including itself, leads to a vast array of molecular architectures.

Understanding the framework of carbon compounds enables chemists to predict and explain their behavior in both natural and synthetic processes. The formation of chains, branches, and rings of carbon atoms allows the creation of an immense variety of organic molecules, from the simplest hydrocarbons to complex proteins that are essential to life.

Molecular Formula: The Blueprint of Molecules

The molecular formula serves as a blueprint, providing crucial information about the number and type of atoms in a molecule. For instance, the molecular formula C₃H₈O indicates a molecule comprises three carbon (C) atoms, eight hydrogen (H) atoms, and one oxygen (O) atom.

Despite the simplicity of a molecular formula, it can represent multiple molecules known as isomers. Isomers have the same atomic composition but differ in the arrangements of atoms. This diversity manifests in structural isomers, where connectivity varies, and can include positional isomers, chain isomers, and functional group isomers, each presenting unique properties and behaviors.

Functional Groups: The Reactive Parts of Molecules

Functional groups are specific clusters of atoms within molecules that possess characteristic reactivity. They are the active sites where chemical reactions occur. Organic molecules may contain multiple functional groups, influencing the molecule's physical and chemical properties.

Some common functional groups include hydroxyl (-OH), found in alcohols; carbonyl (C=O), present in aldehydes and ketones; and halides (such as -Cl, -Br, -F), observed in organohalides. Identifying these groups within a molecular structure can predict reactivity and solubility, and it's pivotal in the naming of compounds using systematic nomenclature.