positional isomer analysis

[olivia]

Hi, can anyone please point me in the right direction of reading material, or explain why positional isomers will have different degrees of pi pi interactions with a phenyl column
Thank you
Liv

[Jumpshooter]

In genral it has to do with the interactions that those isomers have with your column packing material. If the isomers are not modified in some chemical way (e.g., hydrogenation, or adding a hydroxyl group moiety), then they will not be well-resolved on a typical C-18 column. Please try to hydroxylate one of the isomers--then you can better separate them on-column.

[HW Mueller]

Substituents influence the "pi-cloud", they can usually not do this equally from different positions. The polarity will also be different which plays into changes of the pi-system as well. (Furthermore, I very strongly doubt that only pi-pi interactions play a role in separations of a phenyl column).
A book on physical organic chemistry might help.