[monicad95]

Hi, I've seen in lots of 'family trees of isomerism' and even in this video (https://www.youtube.com/watch?v=Ni5IxKIuDnI) where diastereomers and enantiomers go under 'configurational isomers' only. However on this website (http://www.chem.uky.edu/research/gro...reoexamps.HTML) it shows how you can get CONFORMATIONAL diastereomers and enantiomers too (which makes sense to me).
Which one is correct?

Also, could someone please clarify for me the difference between conformational and configurational isomers? I know that conformational isomers are to do with the rotating of sigma bonds and configurational isomers are to do with the breaking of bonds... but looking at isomers of these, it seems like you can just rotate them around?
Thanks!

[kriggy]

Well configurational isomers are isomers with different configuration for example D-galactose and D-glucose have different configuration on carbon 4.

Conformational isomers are isomers where the isomerism is caused by different conformation

the have the same configuration but different conformation

[OrgXemProf]

This, from Eliel, E. H.; Wilen, S. H., "Stereochemistry of Organic Compounds", Wiley:New York, 1994, page  1196 (Glossary):

"Conformational Isomer (conformers). One set of stereoisomers that differ in conformation, that is, in torsion angle or angles. Only structures corresponding to potential energy minima (local or global) qualify." (italics mine.)

Please note that kriggy's example includes an eclipsed conformation, which fails to meet the local-or-global-minimum criterion.

Perhaps a more suitable example of conformational isomerism is provided by the chair-to-chair ring-flip process whereby cis-diaxial-1,3-dimethylcyclohexane equilibrates with cis-diequatorial-1,3-dimethylcyclohexane. The cis-diaxial conformation resides in a local minimum, whereas the cis-diequatorial conformation represents the global minimum for this equilibration process.