Two dimensional resolved

Heteronuclear two-dimensional /-resolved spectra contain the chemical shift information of one nuclear species (e.g., C) along one axis, and its coupling information with another type of nucleus (say, H) along the other axis. 2D /-resolved spectra are therefore often referred to as /,8-spectra. The heteronuclear 2D /-resolved spectrum of stricticine, a new alkaloid isolated by one of the authors from Rhazya stricta, is shown in Fig. 5.1. On the extreme left is the broadband H-decoupled C-NMR spectrum, in the center is the 2D /-resolved spectrum recorded as a stacked plot, and on the right is the con tour plot, the most common way to present such spectra. The multiplicity of each carbon can be seen clearly in the contour plot. 

Values of /CH were also determined by two-dimensional /-resolved spectroscopy using an INEPT-type pulse-sequence,29 with a BIRD pulse for the suppression of "/c H and folding in the F, dimension. Rules for the calculation of the correct values of /c H from the reduced splittings observed were given. The values were also obtained from a set of /-modulated, one-dimensional 13C spectra via the... 

The saturated ring of this phosphate ester has four proton resonances which are shown opposite in a. Because the multiplets are so complex, a two-dimensional /-resolved spectrum was also acquired, b shows the fi-slices (cross-sections) from the /-spectrum and c shows the contour plots. Assign the multiplets and explain their appearance. 

FIG. 14. E.xample of a two-dimensional -resolved proton spectrum, (a) 60 MHz spectrum of a mixture of 45vol" CHjCH,CI, 25vor CH3CH2Br, and 30vol" CH3CH2I. (b) Two-dimensional y-resolved spectrum computed from 64 single echoes represented by 64 sample values, (c) Broad-band decoupled spectrum obtained by projecting the two-dimensional J-resolved spectrum on to the ojj axis. From ref. 150. 

FIG. 20. Two-dimensional resolved C spectrum of n-hexane recorded with the technique indicated in Fig. 19. Twenty-two experiments were co-added for each of the 64 values of t, between 0 and 35 ms. Resolution is severely limited by the 64 x 64 data matrix used to represent the two-dimensional Fourier transform. The absolute values of the Fourier coefficients are plotted. The undecoupled one-dimensional spectrum is indicated along the oi, axis, and the proton-decoupled spectrum is shown along the ujj axis. From ref. 157. 

Selective excitation of a resolved resonance followed by homonuclear or heteronuclear Hartmann-Hahn transfer can also be advantageous in the preparation period of two-dimensional experiments. For example, two-dimensional COSY, NOESY, TOCSY, and two-dimensional /-resolved subspectra of individual spin systems can be acquired based on this principle (Homans, 1990 Sklenaf and Feigon, 1990 Nuzillard and Massiot, 1991 Gardner and Coleman, 1994). In selective two-dimensional experiments like soft COSY (Briischweiler et al., 1987 Cavanagh et al., 1987),... 

The ability to obtain two-dimensionally resolved spectral information is especially important in transient systems such as turbulent combustion systems or scattering from irreproducible plasma discharges (41). The two-dimensional nature of the vidicon is especially useful for experiments such as fluorescence detection with spatial resolution (42). 

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling infonuation analogous to two-dimensional NMR studies) [40]. Time-resolved IR has probed neutrals and ions in solution [41, 42], gas phase kmetics [42] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]- Since vibrational frequencies are very sensitive to the chemical enviromnent, pump-probe studies with IR probe pulses allow stmctiiral changes to... 

Plenary 10. Hiro-o Hamaguchi, e-mail address lilrama ,chem.s.u-tokvo.ac.ip (time and polarization resolved multiplex 2D-CARS). Two-dimensional (tune and frequency) CARS using broadband dye source and streak camera timing. Studies dynamic behaviour of excited (pumped) electronic states. Follows energy flow within excited molecules. Polarization control of phase of signal (NR background suppression). 

Aue W P, Kharan J and Ernst R R 1976 Homonuclear broadband decoupling and two-dimensional J-resolved NMR spectroscopy J. Chem. Phys. 64 4226-7... 

Figure B2.1.9 Two-dimensional time-resolved IR holebiiming speetra obtained with two small polypeptides, apamin and seyllatoxin, by Hoehstrasser and eo-workers [M]- Figure eourtesy Professor R M Hoehstrasser (University of Peimsylvania).

Generally, the most powerful method for stmctural elucidation of steroids is nuclear magnetic resonance (nmr) spectroscopy. There are several classical reviews on the one-dimensional (1-D) proton H-nmr spectroscopy of steroids (267). C-nmr, a technique used to observe individual carbons, is used for stmcture elucidation of steroids. In addition, C-nmr is used for biosynthesis experiments with C-enriched precursors (268). The availability of higher magnetic field instmments coupled with the arrival of 1-D and two-dimensional (2-D) techniques such as DEPT, COSY, NOESY, 2-D J-resolved, HOHAHA, etc, have provided powerful new tools for the stmctural elucidation of complex natural products including steroids (269). 

Figure 2.3. J-resolved two-dimensional C NMR spectra series of a-pinene (1) [in (CDsbCO, 25 °C, 50 MHz],...

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