Cold Organic Chemistry

This proposal ventures into organic chemical reactions under not-so-common conditions, namely in the cold, at insufficient energies, and under the action of hard radiation. As many organic molecules have been discovered in space or brought to earth in meteorites, they must have formed under such conditions through hitherto largely undisclosed mechanisms. One key hypothesis is that quantum-mechanical tunneling (QMT) and novel reactions with exceptionally low barriers are at work. Hence, one of the key objectives is to uncover how QMT, where reactions occur through and not over barriers, controls chemical reactivity and selectivity. A second goal is the examination of cryogenic reactions of hydroxycarbenes or enols with carbonyl compounds. Our methods include organic synthesis of starting materials (also isotopically labelled) and products, infrared as well as ultaviolet/visible matrix-isolation spectroscopy, ab initio computations of structures, spectra, and potential energy surfaces as well as QMT rate calculations. We will examine isotope-selective reactions of competing QMT reactions that can be made selective through strategic isotope incorporation. QMT also offers new ways to activate carbon dioxide and even to catalyze reactions. We propose a unifying synthesis of carbohydrates and alpha-amino acids through a common mechanistic scenario, namely a newly discovered hetero-carbonyl-ene reaction of carbenes or enols in the gas phase. Finally, chemistry far from thermodynamic equilibrium is explored with probing the activation and reaction of highly stable molecules under irradiation with energetic electrons, thereby mimicking conditions of the interstellar medium exposed to galactic cosmic rays. This should shed light on the formation of larger “complex organic molecules” found in this medium and often considered as building blocks for life.