NMR LINESHAPE THEORY OF SUPERIMPOSED INTER-MOLECULAR SPIN EXCHANGE-REACTIONS AND ITS APPLICATION TO THE SYSTEM ACETIC ACID-METHANOL-TETRAHYDROFURAN-D8

The density matrix equations describing the NMR lineshape of tightly coupled spin systems in the presence of intermolecular spin exchange have been recast in a form which is convenient for kinetic studies. The lineshape equation is expressed as a function of pseudo-first-order group exchange rate constants, krs(i), of the spin group i between the environments r and s, of which i is an integral part. Thus, NMR lineshapes are easily calculated even if different exchange reactions such as AB + BD ⇌AC + BD, AB + A*C ⇌ A*B + AC, AB + A*B* ⇌A*B + AB*, AB +CD ⇌ABC + D, etc., are present in the sample. The use of the krs(i) avoids the assumption of reaction mechanisms at the stage of extracting the kinetic data from the NMR lineshape. The presence of any particular reaction set appears as a result of special relations between the krs(i). The utility of this formulation of the lineshape equation is illustrated by the example of the slow intermolecular proton exchange in the system methanol/acetic acid/tetrahydrofuran-d8. © 1979.