2007 Volume 80 Issue 6 Pages 1187-1193
The isomerization process, which is related to racemization of symmetrical 1,2-bis(diaminomethyleneamino)benzenes (=bisguanidinobenzenes) with potential chirality, is caused by bond rotation of aryl–(diaminomethyleneamino) (=aryl–guanidinyl) bond and/or diaminomethylene–imino (=guanidinyl imine) bond. This process was evaluated by temperature-dependent 1H NMR experiments. The guanidinyl imine bond rotation, which is important for the early stage of the inhibition of racemization process, was not restricted by substitution at the ortho-position of the benzene core or alkylation of guanidine function, while protonation of ortho-substituted bisguanidinobenzenes increased the rotation barrier. Changing the guanidine function from cyclic to acyclic caused the rotation about both bonds to become restricted, which could be observed by temperature-dependent 1H NMR experiments.
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