Conformation-changing aggregation in hydroxyacetone: a combined low-temperature FTIR, jet, and crystallographic study |
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Authors: | Sharma Archna Reva Igor Fausto Rui Hesse Susanne Xue Zhifeng Suhm Martin A Nayak Susanta K Sathishkumar Ranganthan Pal Rumpa Row Tayur N Guru |
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Institution: | Department of Chemistry, University of Coimbra, Coimbra, Rua Larga 3004-535, Portugal. asharma@qui.uc.pt |
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Abstract: | Aggregation in hydroxyacetone (HA) is studied using low-temperature FTIR, supersonic jet expansion, and X-ray crystallographic (in situ cryocrystallization) techniques. Along with quantum chemical methods (MP2 and DFT), the experiments unravel the conformational preferences of HA upon aggregation to dimers and oligomers. The O-H···O═C intramolecular hydrogen bond present in the gas-phase monomer partially opens upon aggregation in supersonic expansions, giving rise to intermolecular cooperatively enhanced O-H···O-H hydrogen bonds in competition with isolated O-H···O═C hydrogen bonds. On the other hand, low-temperature IR studies on the neat solid and X-ray crystallographic data reveal that HA undergoes profound conformational changes upon crystallization, with the HOCC dihedral angle changing from ~0° in the gas phase to ~180° in the crystalline phase, hence giving rise to a completely new conformation. These conclusions are supported by theoretical calculations performed on the geometry derived from the crystalline phase. |
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