Question

Which of the following molecules are unsaturated? a. \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) b. \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\) d. \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Short answer

The unsaturated molecules are: b. \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\)

Step-by-step solution

Analyze molecule a.

Look at the carbon-carbon bonds in the molecule: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) There are three carbon-carbon single bonds. Since there are no double or triple bonds between carbon atoms, this molecule is saturated.

Analyze molecule b.

Look at the carbon-carbon bonds in the molecule: \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) There is one carbon-carbon double bond between the second and third carbon atoms. Since there's at least one double bond between carbon atoms, this molecule is unsaturated.

Analyze molecule c.

Look at the carbon-carbon bonds in the molecule: \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\) In this case, we also see a carbon-carbon double bond between the second and third carbon atoms. It has at least one double bond between carbon atoms, therefore it is unsaturated.

Analyze molecule d.

Look at the carbon-carbon bonds in the molecule: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) There are two carbon-carbon single bonds. There are no double or triple bonds between carbon atoms, so this molecule is saturated.

Conclusion

The unsaturated molecules in the given list are: b. \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\)

Key concepts

Carbon-Carbon Double Bonds

Carbon-carbon double bonds are a fascinating and vital part of organic chemistry. They occur when two carbon atoms share two pairs of electrons. This creates a double bond, represented by a double line between the carbon atoms in a chemical structure. These types of bonds are significant because they contribute to the unsaturated nature of the molecule.

Molecules with double bonds have unique geometrical shapes compared to those with only single bonds. A carbon-carbon double bond causes the atoms around it to arrange in a trigonal planar configuration. This results in a 120-degree bond angle around each carbon atom forming the double bond.

Double bonds increase the reactivity of a molecule as they are generally more reactive than their single-bond counterparts. This reactivity is important in many chemical reactions, such as addition reactions, where atoms or groups are added to the carbon atoms forming a double bond.

Chemical Saturation

Chemical saturation refers to the extent to which carbon atoms in a molecule are bonded to hydrogen atoms. In simple terms, a molecule is considered saturated if there are no double or triple bonds between the carbon atoms.

To determine if a molecule is saturated:

• Check the types of bonds between carbon atoms.
• If all carbon-carbon bonds are single bonds, the molecule is saturated.
• Presence of any double (or triple) bond indicates an unsaturated molecule.

Unsaturated molecules, with their double bonds, have the capability of undergoing various chemical transformations. In everyday life, saturated molecules are often found in fats that are solid at room temperature, while unsaturated ones are typically liquid oils.

Molecular Structure Analysis

Molecular structure analysis plays a critical role in understanding the characteristics and behavior of molecules. By examining the structural formula, one can determine whether a molecule is saturated or unsaturated.

To analyze a molecular structure:

• Identify the types of bonds between carbon atoms.
• Look for the presence of double or triple bonds which signal unsaturation.
• Analyze the placement and length of carbon chains which affect molecular properties.

This structural analysis allows chemists to predict the reactivity, physical state, and potential uses of the molecule. Tools such as spectrometry and X-ray crystallography are also used to give a 3D perspective of the molecular structure, adding depth to the analysis.