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Wikipedia lists dipole-dipole, hydrogen bonding and Van der Waals under intermolecular interactions, and hydrophobic, ionic and covalent under intramolecular interactions.

  1. Is there a clear distinction between each and every one of these interactions? For example: isn't hydrogen bond a private case of VdW? aren't ionic bonds and hydrophobic interactions private cases of dipole-dipole interaction?
  2. Is there one single chart that differentiates all of these types of interaction?
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No, there aren't clear distinctions, particularly between intramolecular and intermolecular interactions.

First, a caveat that we generally divide molecules along covalent bonds. So those are strictly intramolecular, in my opinion. (Network solids are a bit tricky to classify.)

Let's go through the rest one at a time.

  1. Dipole-dipole: These are usually intermolecular, but certainly in larger, more flexible molecules, intramolecular polar-polar interactions can change the molecular shape and preferred conformation. (Think about tying together two bar magnets on one piece of string. Certainly they'll interact.)

  2. Hydrogen bonds: Yes, many of these are intermolecular. However, there definitely are intramolecular hydrogen bonds:

enter image description here

  1. Van der Waals: Again, these can be intermolecular. In even a moderate molecule, intramolecular non-bonded van der Waals interactions can change conformations and geometries. Consider axial/equitorial preferences in cyclohexanes or other types of "steric clashes" because of big bulky groups. These are the effects of van der Waals interactions.

OK, so all the intermolecular interactions are also intramolecular ones too.

  1. Hydrophobic interactions: I usually think of these as intermolecular but similar considerations make sense as intramolecular for the reasons I outline under van der Waals interactions above.

  2. Ionic: I'll just think of these as different partial charges in a molecule. Clearly electrostatic interactions occur both inside a molecule (e.g., electrostatic non-bonded interactions changing conformations and geometries) and as intermolecular forces, e.g., water-cation interactions.

So besides covalent interactions, which we use to divide "inside" and "outside" a molecule, all of these are both intermolecular and intramolecular interactions.

I'm not sure I've seen a great chart. Maybe someone else can comment.

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  • $\begingroup$ I've read that it's not vdW repulsion in ethane that causes the molecule to favor a staggered conformation but rather hyperconjugation ...your thoughts? $\endgroup$
    – Dissenter
    Feb 6, 2015 at 3:40
  • $\begingroup$ nature.com/nature/journal/v411/n6837/full/411565a0.html $\endgroup$
    – Dissenter
    Feb 6, 2015 at 3:42
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    $\begingroup$ Definitely hyperconjugation and other effects can cause conformational preferences. But there are definitely longer range VdW steric effects, eg substitutions around the inter-ring bond in biphenyls. $\endgroup$
    – Geoff Hutchison
    Feb 6, 2015 at 4:08
  • $\begingroup$ I came across this chart, which seems to differentiate firstly by "basis of attraction" and secondly by bond energy, and it seems that anything above 600kJ/mol is intramolecular, and anything below 75kJ/mol is intermolecular. What do you think? $\endgroup$
    – Sparkler
    Feb 6, 2015 at 5:45
  • $\begingroup$ While these trends may be largely true, for the reasons I give above, all the interactions can be both intermolecular and intramolecular. $\endgroup$
    – Geoff Hutchison
    Feb 6, 2015 at 12:47

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