Arrange the following compounds in order of increasing boiling point: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\), \(\mathrm{C}\left(\mathrm{CH}_{3}\right)_{4}\). Explain your reasoning.

To understand why substances have different boiling points, it's essential to start with intermolecular forces (IMFs). These are forces of attraction or repulsion which act between neighboring particles, such as molecules, atoms, or ions. IMFs are responsible for holding substances together and are crucial in determining the properties of a substance, including boiling point.

There are several types of IMFs, with varying strengths. The key types include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Hydrogen bonds are the strongest of these, occurring when hydrogen is covalently bonded to a highly electronegative atom. Dipole-dipole interactions occur between polar molecules, where partial charges attract each other.

However, all molecules, regardless of polarity, are subject to London dispersion forces. These are the weakest intermolecular forces and are a result of the temporary dipoles that occur when electrons happen to be more concentrated in one area of a molecule than another. These momentary shifts in electron density create temporary attractions between molecules.

The molecular structure refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold them together. It significantly impacts IMFs, and therefore, the physical properties of a substance, including its boiling point.

When considering boiling points, the shape of a molecule and its ability to pack closely with other molecules become important. Linear and symmetrical molecules are able to stack together effectively, which maximizes the interaction between them and enhances the London dispersion forces. In contrast, branched molecules have irregular shapes that don't pack as tightly, resulting in fewer interactions and weaker dispersion forces.

The more surface area two molecules have in contact, the stronger the dispersion forces will be. Hence, a linear molecule typically has a higher boiling point than its branched counterparts when other factors such as molar mass and polarity are held constant.

London dispersion forces are a type of van der Waals force and are sometimes referred to as induced dipole-induced dipole attractions. They are an especially important consideration when nonpolar molecules are involved because these molecules don't have permanent dipoles for other types of intermolecular attractions.

Every molecule experiences fluctuations in electron distribution, which can momentarily create a dipole. When this temporary dipole induces a dipole in another nearby molecule, it leads to an attraction between them. Factors that affect the magnitude of London dispersion forces include:

• The number of electrons in the molecule: More electrons mean a higher probability of fluctuations, thus stronger forces.
• The size of the molecules: Larger molecules have more surface area, hence more opportunities for interactions.
• The shape of the molecule: More contact between molecules results in stronger forces. Linear molecules typically have stronger London dispersion forces than branched molecules with the same molecular formula.

Understanding these forces explains why n-pentane, being linear, has the highest boiling point among the given compounds, followed by isopentane and then neopentane due to their increasing branching and decreasing surface area for molecular interactions.