Problem 109 - General Chemistry: Principles and Modern Applications

Question

Which hydrocarbon has the greater number of isomers, \(\mathrm{C}_{4} \mathrm{H}_{8}\) or \(\mathrm{C}_{4} \mathrm{H}_{10} ?\) Explain your choice.

Step-by-Step Solution

Answer

The hydrocarbon C4H8 has a greater number of isomers. It has four isomers while C4H10 has only two.

Step 1: Determine isomers for C4H8

First, determine the different structures that can be formed with C4H8. This marks the hydrocarbon as an alkene due to the presence of a double bond. And by drawing the structures, we find that there are four isomers for C4H8.

Step 2: Determine isomers for C4H10

Next, determine the different structures that can be formed with C4H10. The hydrocarbon is an alkane, and it doesn't include multiple bonds. By drawing the structures possible, we find that there are two isomers for C4H10.

Step 3: Compare the number of isomers

Once all possible isomers for C4H8 and C4H10 are determined, we compare the number of isomers for each hydrocarbon.

Key Concepts

Alkenes and Alkanes

Understanding the distinction between alkenes and alkanes is crucial in the study of organic chemistry. Alkanes are hydrocarbons that contain only single bonds between carbon atoms.

These are called saturated hydrocarbons, as they contain the maximum number of hydrogen atoms possible for the given number of carbon atoms. An example of an alkane is methane, \text{(CH\(_4\))}.On the other hand, alkenes are unsaturated hydrocarbons that include at least one double bond between carbon atoms, which reduces the number of hydrogen atoms in the molecule. Because of this feature, alkenes generally have fewer hydrogen atoms than an alkane with the same number of carbon atoms. For example, ethene \text{(C\(_2\)H\(_4\))} is an alkene with a double bond.The presence of double bonds in alkenes gives them distinct chemical properties compared to alkanes, such as a higher reactivity due to the double bond being a site of chemical activity.

Structural Isomerism

Structural isomerism is a form of isomerism where isomers contain the same number of atoms of each element \text{(molecular formula)} but have different arrangements of their atoms or different types of bonds and bonding patterns between atoms. This means an alkane and an alkene can have the same molecular formula but different structures. For example, \text{(C\(_4\)H\(_8\))} is the molecular formula for both butene, an alkene, and isobutane, an alkane isomer.One critical aspect of structural isomerism is that the isomers can exhibit markedly different physical and chemical properties, despite having the same molecular formula. This is because the shape and type of bonding influences how the molecules interact with other substances and how they react in chemical processes.

Molecular Formula

The molecular formula provides the exact number of each type of atom in a molecule. It is a basic representation of a compound's composition and is used to discern different compounds and their isomers.

For instance, alkenes and alkanes can have the same molecular formula but are different types of compounds with unique properties and structures. The molecular formula does not provide information on the compound's structure; it only gives the ratio of atoms. This is where structural formulas and structural isomerism become important for a deeper understanding. They elucidate how the atoms within a molecule are connected, allowing chemists to predict and explain the behavior of different isomers in chemical reactions and in different physical states.