Modeling rate-controlling solvent effects. The pericyclic meisenheimer rearrangement of N-propargylmorpholine N-oxide.
The activation parameters of the pericyclic Meisenheimer rearrangement and a competitive rearrangement of N-propargylmorpholine N-oxide were determined by experimental and computational methods. A number of aprotic and protic solvents of different polarities and hydrogen bond-forming abilities and the roles of electron-pair acceptor additives were investigated. The reaction kinetics were followed by means of NMR. In protic solvents, isotope-labeling experiments revealed a novel inverse secondary kinetic isotope effect (k(H)/k(D) about 0.8) for the rate-determining cyclization step, probably occurring because of a C(sp) --> C(sp(2)) change in hybridization at the reaction center. In molecular computations at the B3LYP/6-31++G(d,p) level of theory, implicit, explicit, and joint explicit-implicit solvent models were used. The explicit-implicit model and molecular dynamic simulations gave the most accurate results. The components of the rate-controlling solvent effect are discussed, and general equations are proposed for accurate prediction of the solvent-dependent activation parameters.
Mucsi
Zoltán
Z
Department of Organic Chemistry, Eötvös Loránd University, Budapest, Hungary. icsizmad@jgytf.u-szeged.hu
Szabó
Anna
A
Hermecz
István
I
Kucsman
Arpád
A
Csizmadia
Imre G
IG
D003497:Cyclic N-Oxides / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D009019:Morphinans / Q000737:chemistry*; D009025:Morpholines / Q000737:chemistry*; D012995:Solubility; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
D003497:Cyclic N-Oxides; D009019:Morphinans; D009025:Morpholines; C440369:N-propargyl; D012997:Solvents