Diketopiperazines bearing a benzyl moiety with different para-substituents were synthesized and analyzed by H-1 NMR spectroscopy. All of these diketopiperazines were found to adopt a folded conformation according to the upfield chemical shift of the cis-proton (cis to the benzyl moiety) due to a shielding effect in the H-1 NMR spectra. An intramolecular CH-pi interaction appears to be an important factor for the folded conformation due to the effects of para-substituents on the benzyl group.