DEPT

Abstract: Unambiguous and complete assignments of 1H and 13C NMR chemical shifts for stigma-5-en-3-O-β-glucoside, isolated from Brassica rapa sb.sp. campestris and Aloe barbadensis, and its acetyl derivative are presented, based on DEPT, HETCOR, COLOC, HMBC, COSY-45°, NOESY and J-resolved experiments. Copyright © 2001 John Wiley & Sons, Ltd.

Abstract: Publisher Summary Silicon-29 nuclear magnetic resonance (NMR) is a highly valuable form of spectroscopy for organosilicon compounds; it is only now becoming a routine technique. Silicon nuclei that are coupled to protons, the NMR spectrum can be greatly improved by the transfer of polarization from 1 H to 29 Si. Polarization transfer techniques have been available for over a decade, they have not been widely used to obtain 29 Si-NMR spectra. J-cross polarization (JCP), which evolved from methods used for enhancing the solid-state spectra of rare spin nuclei, has been applied to 29 Si-NMR spectroscopy. Selective polarization transfer (SPT) is another NMR technique recently used to obtain enhanced 29 Si-NMR spectra. To obtain SPT spectra, a silicon satellite of a proton signal is selectively irradiated prior to a nonselective 29 Si pulse. Two new polarization transfer techniques have recently been reported: insensitive nuclei enhanced by polarization transfer (INEPT) and distortionless enhancement by polarization transfer (DEPT). There are differences between the INEPT and DEPT techniques; the fundamental polarization transfer mechanism is the same. Dodecamethylcyclohexasilane was chosen as a representative member of this important class of compounds upon which to test INEPT and DEPT methods. Siloxanes represent another large class of silicon compounds for which 29 Si-NMR data would be useful. Bendall, Pegg, and Doddrell showed that the results of multipulse sequences, such as INEPT and DEPT, can be analyzed using the Heisenberg vector approach. DEPT theory is best described mathematically. Two different analyses have been employed: the Schrodinger approach and the Heisenberg approach.

Abstract: The DEPT technique for the generation of CH, CH, and CH C NMR subspectra has enabled the resolution and assignment of broad and overlapping aliphatic resonances in copolymers. For styreneacrylonitrile copolymers, the CH resonances gave dyad fractions that were in agreement with the previously established copolymer structure. For styrene-maleic anhydride copolymers, three broad resonances were observed in the methylene subspectrum. These resonances were assigned to SSS, SSM and MSS, and MSM triads in preference to SS, trans-MS, and cis-MS dyads on the basis of a variety of evidence. This sequence information can be applied to the study of the mechanism of copolymerization. Partial esterification of the anhydride unit in some styrene-maleic anhydride copolymers was detected by generating the CH subspectrum. A modification of the DEPT sequence to obtain partially relaxed subspectra enabled T and T relaxation times of both C and H nuclei to be measured for each of the resolved resonances.