Polarity and Intermolecular Forces

Cinnamaldehyde is a polar molecule comprised of carbon, hydrogen, and oxygen. Therefore, (1) dispersion forces, (2) dipole-dipole interaction, and (3) hydrogen bonding all have the potential to occur between Cinnamaldehyde and another molecule. Dispersion forces, dipole-dipole interaction, and hydrogen bonding are the three main intermolecular forces of attraction that naturally take place between adjacent molecules. The phrase "opposites attract" is relevant in the case of intermolecular forces as a positive end of one molecule is attracted to a negative portion of an adjacent molecule.

(1) Dispersion forces occur between every pair of adjacent molecules, both polar and non-polar, and can be referred to as "temporary dipole moments." These moments resolve themselves and are instantaneous and temporary. Cinnamaldehyde and whichever molecule it happens to be adjacent to at a given moment will experience dispersion forces between one another.

(2) Dipole-dipole interaction is an intermolecular force stronger than dispersion forces. Polar molecules experience these "permanent dipole moments," while non-polar molecules do not. Because Cinnamaldehyde is polar, it is attracted to adjacent polar molecules through dipole-dipole interaction.

(3) Hydrogen bonding is a specific and especially strong type of dipole-dipole interaction. Hydrogen bonding takes place between a hydrogen atom of one polar molecule and a nitrogen, oxygen, or fluorine atom of an adjacent polar molecule. Cinnamaldehyde possesses eight hydrogen atoms and one oxygen atom, so its hydrogen atoms may experience hydrogen bonding between a nitrogen, oxygen, or fluorine atom of an adjacent molecule, and its sole oxygen atom may experience hydrogen bonding between a hydrogen atom of an adjacent molecule.

Ethane, a non-polar molecule

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Cinnamaldehyde, a polar molecule

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Water, a polar molecule comprised of hydrogen and oxygen

Boron trifluoride, a polar molecule