Si-29 NMR spectra of trimethylsilyl and tert-butyldimethylsilyl derivatives of purines and pyrimidines

Trimethylsilyl and tert-butyldimethylsilyl derivatives of naturally occurring purines and pyrimidines and also other closely related model compounds were prepared and their Si-29 NMR spectra measured. Only the chemical shifts of the Si-NH- moiety could be assigned experimentally (i.e. exactly); the chemical shifts of Si-O- and Si-N- fragments could be assigned only on the basis of chemical shift correlations. The Si-N- lines are surprisingly narrow in all derivatives of nucleic bases studied. The lines are narrow because of the 'self decoupling' of fast relaxing N-14 nuclei. The values of Si-29, N-15 coupling constants could not be reliably determined (by the HEED-INEPT method), nor could the Si-N lines be completely assigned in these compounds. Measurement of Si-29 NMR spectra is shown to be a sensitive and fast method for checking completeness of silylation of nucleobases or their analogues. Assignment difficulties limit other applications. (C) 1998 John Wiley & Sons, Ltd.status: publishe

IR laser therlomytic conversion of disiloxanes to polyoxocarbosilane phase and silicon carbide

International audienceContinuous-wave CO2 laser irradiation into gaseous methyldisiloxanes [(CH3)nH32nSi]2O (n ~ 2,3) at 1000 uC yields nanosized Si/C/O–carbon composites and at 2000 uC affords SiC–Si/C/O–carbon composites. The results demonstrate the feasibility of the direct production of silicon carbide from disiloxanes and suggest that the laser-induced homogeneous thermolysis of disiloxanes to SiC can be a preferred alternative to the earlier reported conventional thermolysis of specially synthesized polysiloxanes