Polarity

From the above information on intermolecular interactions it follows that a simple distinction between non-polar and polar molecules is not sufficient. Instead we must distinguish between molecules that are apolar (i.e. neither H−bond donor nor H−bond acceptor), monopolar (either H−bond donor or H−bond acceptor), or bipolar (both H−bond donor and H−bond acceptor). A classification of a compound can usually already be done when its structural formula is known, for example:

• All compounds that contain an H−atom in form of a −OH or −NH group are H−bond donors.
• Compounds containing oxygen or nitrogen are strong H−bond acceptors.
• Compounds with pi−electrons are weak H-bond acceptors.

Table: Examples for the different abilities of organic compounds to interact by van der Waals and H−bond interactions.

¹ Intramolecular H-bonds like in 2-nitrophenol strongly reduce the ability of the compound to form H−bonds with neighboring molecules.
² Compounds whose pi-electron density is diminished by electron withdrawing substituents are apolar.

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