PubMed · 14896047
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J WALTON. 1952-01-12. The basic principles of atomic structure.. https://doi.org/10.1136/bmj.1.4749.99
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We prove here a new transient-state kinetic rule which states that the ratios of the first derivatives of kinetic isotope effect time courses, extrapolated to zero time, provide integral values which specify the precise step number in the reaction sequence in single isotope substituted reactions. This rule defines such absolute numbers even where the steps involved are too fast to provide measurable concentrations of intermediates and when the full reaction sequence is unknown.
Solution 29Si NMR spectroscopy results of zeolite precursor solutions of composition 1 SiO2:4 C2H5OH:0.36/n R+n[OH-]n:20 H2O are reported. This work employs isotopically enriched 29Si materials to aid in spectral interpretation. Using both 1D and 2D methods, spectra of solutions containing tetrapropylammonium hydroxide are wholly consistent with the existing silicate chemistry literature and indicate that the majority of the species are high-symmetry silicate clusters previously observed in aqueous solutions. The results are inconsistent with the nanoblock or nanoslab model proposed by Kirschhock and co-workers. Mixtures containing the 4,4'-trimethylene-bis(1,1'-dimethylpiperidinium) dihydroxide cation were also studied. These mixtures have similar speciation to the TPA solutions, although the relative populations of the species are different. Preliminary variable temperature 29Si NMR of these mixtures shows that the exchange properties of the high-symmetry silicate species, most notably the tetrahedral tetramer, depend on the organocation identity.