Which type of intermolecular force predominates in hydrocarbons?

Which type of intermolecular force predominates in hydrocarbons?

• A. Hydrogen Bonding
• B. Dipole-Dipole
• C. Ion-Dipole
• D. London Dispersion Forces

Answer: (D)

Nonpolar hydrocarbons depend mainly on London dispersion forces. Since carbon–hydrogen molecules are largely nonpolar, there are no permanent dipoles to attract each other strongly. The attractive force comes from temporary fluctuations in electron density that create instantaneous dipoles, which then induce dipoles in neighboring molecules—producing dispersion forces. Hydrogen bonding requires H attached to highly electronegative atoms like oxygen or nitrogen, and dipole-dipole interactions need polar molecules, neither of which applies to hydrocarbons. Ion-dipole interactions involve ions, which aren’t present in neutral hydrocarbons. So the prevailing intermolecular force for hydrocarbons is London dispersion forces, which grow stronger with greater molecular size and surface area.

Nonpolar hydrocarbons depend mainly on London dispersion forces. Since carbon–hydrogen molecules are largely nonpolar, there are no permanent dipoles to attract each other strongly. The attractive force comes from temporary fluctuations in electron density that create instantaneous dipoles, which then induce dipoles in neighboring molecules—producing dispersion forces. Hydrogen bonding requires H attached to highly electronegative atoms like oxygen or nitrogen, and dipole-dipole interactions need polar molecules, neither of which applies to hydrocarbons. Ion-dipole interactions involve ions, which aren’t present in neutral hydrocarbons. So the prevailing intermolecular force for hydrocarbons is London dispersion forces, which grow stronger with greater molecular size and surface area.