AI Article Synopsis
- The study investigates the formation of hemiacetals using pyrazine trifluoromethylketone and various simple alcohols through quantum chemical calculations and NMR spectroscopy.
- Four mechanistic pathways for hemiacetal formation were evaluated, highlighting an assisted proton transfer process with a pseudo eight-membered transition state that aligns well with experimental results.
- A new pathway involving a five-membered transition state and zwitterionic intermediates is proposed, while the direct proton transfer in a pseudo four-membered transition state is dismissed due to its high energy compared to other pathways.
Article Abstract
The formation of hemiacetals from pyrazine trifluoromethylketone as a model receptor and four simple alcohols was studied by using quantum chemical calculations and NMR spectroscopy. Free energy profiles for four types of mechanistic pathways were calculated and discussed with respect to kinetic and thermodynamic measurements. We show that hemiacetal formation is facilitated by an assisted proton transfer process a pseudo eight-membered transition state which brings the theory and experiment into close agreement. Also, a newly proposed mechanistic pathway for hemiacetal formation a five-membered transition state leading to zwitterionic intermediates is discussed. Direct proton transfer in a pseudo four-membered transition state can be ruled out due to the high energy of transition states with respect to other mechanistic pathways. We also show that in the case of hemiacetals, water and alcohol molecules cannot account sufficiently for the H-transfer process six-membered transition states.
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| http://dx.doi.org/10.1039/d3ob00668a | DOI Listing |
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