Roger Lalancette

Our research interests include small-molecule structure elucidation by single- crystal X-ray diffraction techniques, medium-size molecules (up to 100 atoms), as well as macromolecules (protein and peptide-chain structural information), and GC/MS of pesticides in soil and water samples at the part- per-trillion level.

Our most recent work centers on the prediction of the type of intermolecular hydrogen bonding that exists in cyclic keto carboxylic acids. This prediction is based on the solid-state infrared spectrum (KBr pellet or neat powder) compared to the solid-state Raman spectrum, and subsequent proof of structure by lower-temperature (-30 C) single-crystal X-ray analysis. We have found only one example of intramolecular hydrogen-bonding in this type of molecule; mostly, we have found that hydrogen bonding forms either as a chain (catemer) from the acid proton of one molecule to the carbonyl oxygen of the next molecule, typically along a screw axis, or as an acid dimer leaving the carbonyl oxygen non-hydrogen-bonded.

We have demonstrated that the symmetry-based differences between solid-state IR and solid-state Raman spectra may be used reliably to differentiate those acids with dimeric H-bonding from those with non-centrosymmetric H-bonding patterns.