Which of the following diagrams best represents a set of polar molecules interacting through dipole–dipole interactions?

• A. Molecules are shown with no specific orientation, randomly distributed.
• B. Molecules are shown interacting only through hydrogen bonds between hydrogen and oxygen atoms.
• C. Molecules are shown with all positive ends grouped together and all negative ends grouped together.
• D. Molecules are shown with positive and negative ends aligned so that the positive end of one molecule is near the negative end of another.

Answer: (D)

Verified step by step guidance

1. Understand that dipole–dipole interactions occur between polar molecules, where the positive end of one molecule is attracted to the negative end of another molecule.
2. Recognize that for dipole–dipole interactions to be represented correctly, molecules must be oriented such that their opposite charges (partial positive and partial negative) are near each other, showing an alignment of dipoles.
3. Eliminate diagrams where molecules are randomly oriented with no specific alignment, as this does not represent the directional nature of dipole–dipole forces.
4. Exclude diagrams showing only hydrogen bonding, since hydrogen bonding is a specific, stronger type of dipole interaction involving hydrogen and highly electronegative atoms like oxygen or nitrogen, not general dipole–dipole interactions.
5. Avoid diagrams where all positive ends cluster together and all negative ends cluster together, because like charges repel and this arrangement is not energetically favorable for dipole–dipole interactions.