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Would you expect a dipole moment determined in solution to be different from that in an isolated molecule? If so, why?

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    $\begingroup$ In short, yes. In more detail, that would depend greatly on the nature of the solvent (polar or non-polar, etc.) $\endgroup$ – Ivan Neretin Mar 31 '16 at 17:24
  • $\begingroup$ To mention a prominent example: For water it is suggested that the increase in dipole moment upon solvation "originates from the decrease of the angle between the dipole vectors of the lone pairs on oxygen as the number of hydrogen bonds to that oxygen increases. Thus, the decreased angle, and the consequent increase in water dipole moment, is most likely to occur in environments with a larger number of hydrogen bonds, such as the center of a cluster of water molecules" (see: here). $\endgroup$ – Philipp Mar 31 '16 at 18:06
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I've actually been investigating this in my comp chem coursework. A large dielectric can support more charge separation and therefore stronger dipoles, but the effect diminishes. Going from an $\epsilon$ of 2 (cyclohexane) to 9 (DCM) gives a much bigger change in dipole than going from 9 to 80+ (water).

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