Structure, conformation, and dynamics of P,N-containing cyclophanes in solution.

3D structures in solution of highly symmetrical N,P-containing macrocycles were established by a variety of 2D NMR correlation techniques. It was shown that a number of magnetically equivalent fragments in such symmetrical systems can be estimated by NMR diffusion measurement. The title compounds adopt a helical conformation of the macrocycles in solution.

Preferential protonation and methylation site of thiopyrimidine derivatives in solution: NMR data.

Protonation (alkylation) sites of several thiopyrimidine derivatives were directly determined by 1H-15N (1H-13C) heteronuclear single quantum coherence/heteronuclear multiple bond correlation methods, and it was found that in all compounds, protonation (methylation) occurred at the N1 nitrogen. GIAO DFT chemical shifts were in full agreement with the determined tautomeric structures. According to ab initio calculations, the stability of the different protonated forms and methylated derivatives was favored due to thermodynamic control and not kinetic control.