3,3-Disubstitued oxetanes 2a, 2j and 2q were further characterized by X-ray crystallography and compared to known analogous phenone structures, which displayed interesting differences in conformation (Figure , also see Supplementary Information pages S75-S81). The 3,3-disubstituted oxetane derivatives adopt a conformation with increased 3-dimensional nature. Most notably the aromatic ring on the oxetane is almost orthogonal to the pseudo-carbonyl plane (dihedral angle between Ooxetane-Cqoxetane-Cqaromatic-CHaromatic), whilst in the ketone, the aromatic ring is aligned with the plane as to maximize favorable p-conjugation. Furthermore, the increased steric bulk of the oxetane group together with the decreased steric requirement of the 'twisted' aromatic ring induce a switch in the preferred conformation of the CH2CHRR' chain, which now lies on the side of the aromatic instead of the carbonyl (oxetane). The conformational preferences in the X-ray structures of 2a, 2j and 2q did not seem to be influenced significantly by crystal packing effects, as revealed by analysis of intermolecular interactions in 2a, 2j and 2q (Supporting Information pages S75-S81).