• Study of multi-site chemical exchange in solution state by NMR: 1D experiments with multiply selective excitation

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      Permanent link:
      https://www.ias.ac.in/article/fulltext/jcsc/122/04/0471-0480

    • Keywords

       

      Chemical exchange; solution state; 1D NMR; modulated shaped RF pulses; multi-site selection; sign labelling.

    • Abstract

       

      Chemical exchange in solution state has been investigated traditionally by both 1D and 2D NMR, permitting the extraction of kinetic parameters (e.g. the spin-lattice relaxation time $T_1$, the exchange rate constant 𝑘 and the activation parameters). This work demonstrates a simple 1D NMR approach employing multiply selective excitation to study multi-site exchange processes in solution, applying it to systems that exhibit three-site exchange. This approach involves simultaneous excitation of all - or a chosen subset of - the exchanging sites by using an appropriately modulated shaped radiofrequency pulse. The pulse sequence, as well as analysis is summarized. Significant features of the experiment, which relies on sign labelling of the exchanging sites, include considerably shorter experiment time compared to standard 2D exchange work, clear definition of the exchange time window and uniform pulse non-ideality effects for all the exchanging sites. Complete kinetic information is reported in the study of dynamic processes in superacid solutions of two weak bases, studied by 1H NMR. An analytical solution, leading to the determination of four rate parameters, is presented for proton exchange studies on these systems, which involve a mixture of two weak bases in arbitrary concentration ratio, and stoichiometric excess of the superacid.

    • Author Affiliations

       

      Samanwita Pal1

      1. Department of Chemistry, Indian Institute of Technology - Madras, Chennai 600 036
    • Dates

       
  • Journal of Chemical Sciences | News

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