Question

Conformers sometimes differ in chemical reactivity. For example, only certain alkyl bromide conformers have the appropriate geometry to undergo elimination via an E2 mechanism. I imagine that conformers differ in physical properties as well, for example I think they might have different dipole moments, differing abilities to form hydrogen bonds, and differing abilities to pack together (if any of these are not true please let me know), leading to different melting and boiling points.

If a molecule can rapidly convert between different conformers, are the properties of the molecule that we observe a weighted average of the properties of the conformers, with the most stable conformers contributing the most to the properties? Could there be some kind of "synergistic" effect, where, for example, two different conformers are able to hydrogen bond well with each other, leading to a lower overall boiling point than the boiling point of any individual conformer? If this synergy is present, could it lead to conformers that we would expect to be high in energy based on steric arguments actually being lower in energy than we expect due to interactions with other conformers, and due to this lowered energy, the molecules might become this conformer more frequently?

Answer 1

Yes, the properties of a molecule that rapidly interconverts between conformers are generally a weighted average of the conformers' properties, with the most stable conformers contributing the most. Synergistic interactions between conformers can also influence their stability and the overall physical properties of the molecule, impacting both theoretical understanding and industrial applications.

Step-by-step explanation:

Conformational isomers, or conformers, are different spatial arrangements of a molecule that result from rotation around single bonds. These conformers can indeed have their unique individual properties like dipole moments, abilities to form hydrogen bonds, and packing abilities in solids, impacting their melting points and boiling points.

For a molecule that can rapidly interconvert between different conformers, the observed physical properties tend to be a weighted average of the properties of the individual conformers. Generally, the most stable conformers contribute the most.

However, when considering how these conformers can affect the overall properties of a molecule, it's important to remember that the intermolecular interactions, such as hydrogen bonding between two different conformers, can indeed lead to properties that don't exactly match any single conformer's properties.

There may also be cases of synergistic effects where the interactions between different conformers result in a more stable mixture than might be predicted by the stability of individual conformers alone. Such synergistic interactions can influence the overall energy landscape of the molecule and thus affect the frequency of each conformer's occurrence.

This can be an important consideration in both the theoretical understanding and the industrial application of chemical compounds.