DEPT-INADEQUATE

There are a large number of structural parameters for NMR of different nuclei and many examples of how they can be applied to the analysis of hydroxylamines, oximes and hydroxamic acids. Fortunately though, there are many very clear, meticulously written descriptions of INEPT, DEPT, INADEQUATE, COSY, NOESY and the like, in one- and two-dimensional NMR spectroscopy, that are cited in the references. Since their content is beyond the scope of the present chapter, a brief mention of some of the fundamental concepts that are essential for its understanding by the nonspecialist is in order. 

Figure 13 Pulse sequences of -detected IPAP DEPT-INADEQUATE.The insert is used when in-phase doublets are acquired. The filled and open rectangles represent 90° and 180° rectangular pulses, respectively, applied from the x-axis unless stated otherwise. The dashed rectangles of the DEPT pulse sequence represent rectangular pulses with flip angle 6 = 90° or 45°. The 180° BIBOP pulses are indicated as wide rectangles with a sine wave. The 13C adiabatic inversion pulses are designated by an inclined arrow. The following delays were used t = 0.5/Vch> At = 0.25/VCo A2 = 0.25/ycc. For other parameters see Ref. 31. Reproduced by permission of Elsevier.

Figure 14 Determination of interglycosidic coupling constants of Me-/ -D-lactoside, shown in the inset, using F1 traces from IPAP DEPT-INADEQUATE spectra. The long-dashed lines are the sum or the difference of the in-phase (solid line) and anti-phase doublets (short-dashed line).

The hydrolysis of 3-ethoxy-4-ethylbicyclo[4.1.0]hept-4-en-7-one propylene acetal (1) with aqueous acetic acid in tetrahydrofiiran gives an oil with the molecular formula CnH/gOi, from which the INADEQUATE contour plot 22 and DEPT spectra were obtained. What is the compound ... 

The correlation signals of the INADEQUATE experiment directly build up the ring skeleton A of the compound. Elere characteristic C shifts (5c = 123.1, 137.6 148.9, 109.1) establish the existence and position of two double bonds and of one tetrahedral C-0 single bond (5c = 70.5). DEPT spectra for the analysis of the CH multiplicities become unnecessary, because the INADEQUATE plot itself gives the number of CC bonds that radiate from each C atom. 

A constant evolution period t, is the new feature of. /-modulated spin-echo, DEPT, and INADEQUATE sequences. During this time period, a 7-modulation or a polarization transfer may evolve. Such pulse sequences provide FID signals S(t2) which are still functions of one variable time t2. The Fourier transforms, however, are NMR spectra with specific information, depending on the constant evolution period ti. One simple example is the generation of the quaternary carbon-13 subspectrum by means of a. /-modulated spin-echo experiment with an evolution time of tj2 = x = as in... 

Fig. 2.59. Tracing out the carbon skeleton of C10H20O by a two-dimensional INADEQUATE experiment in combination with two DEPT experiments (100.6 MHz (a b) 400 mg in 1 mL, (c-e) 50 mg in 0.4 mL of deuteriochloroform at 30CC measuring time for (a) 14 h transform time 50 min) (a) contour plot of the INADEQUATE matrix (b) subspectra of all 13C — 13C bonds u k (c) proton-decoupled 13C NMR spectrum (d -e) DEPT experiments for generation of a CH carbon subspectrum (d) and for separation of CH2 carbon atoms (negative) from CH and CH3 groups (positive).

Fig. 2.60. Deriving the carbon skeleton of an organic compound by DEPT and 2D-IN-ADEQUATE with COSY-like square correlations sample 3-(isopinocampheoxy)-2-methyl-l,3-butadiene, 400 mg in 0.4 mL of hexadeuterioacetone, 100.6 MHz (a) proton-broadband decoupled spectrum (1 scan) (b) DEPT subspectrum of CH carbon nuclei (8 scans) (c) DEPT spectrum with CH, CH3 (positive), and CH2 (negative. 8 scans) (d) 2 D-INADEQUATE experiment of aliphatic carbon nuclei, 256 experiments, 64 scans per experiment. The bicyclic partial structure of the molecule can be derived from the square correlations (e.g.. .. —44.2 — 81.1 —35.6—. ..). A stacked plot of the carbon-proton shift correlation of this sample is displayed on the cover.

Modern techniques.. /-Modulated spin-echo ( APT ), non-selective polarization transfer ( DEPT ) experiments and two-dimensional carbon-proton, proton-proton ( COSY ) and carbon-carbon ( 2D-INADEQUATE ) shift correlations are in use (see the following section) and will be used in order to clarify doubtful signal assignments (see Sections 2.9 and 2.10). 

Identify the compound C8H9N02 from its H, 13C/DEPT, COSY, HMQC, and INADEQUATE spectra and show all correlations. 

DEPT to enhance the signal of some other experiment in the sections devoted to those experiments (e.g. heteronuclear correlations, INADEQUATE, DQF COSY, 7-resolved spectra). Similarly, an INEPT experiment can be made selective in a number of ways some are discussed in Section VI.C.l on selective experiments. 

NMR spectra have been used frequently to elucidate and/or confirm the structures of these heterocycles, but little or no systematic study had been done. A detailed study of l3C NMR spectra by distortionless enhancement by polarization transfer (DEPT), inverse H-I3C coherence transfer experiments (HMQC and HMBC) and by INADEQUATE of factor F0 has been reported <91JBC9622>. The 13C NMR spectra of a series of pyrido[4,3-J]pyrimidines were interpreted on the basis of a detailed study of other analogues <91JCS(P2)1559>. Carbon-13 NMR spectroscopy has been used to indicate the site of alkylation of pyrido[2,3-c]pyridazin-4-ones <90CPB3359>. 

The INEPT-COS-INADEQUATE (Figure 8 B), which is in terms of sensitivity equivalent to the 1,1-ADEQUATE,37 outperforms (relative sensitivity of 0.325) the INEPT-INADEQUATE experiments only for HiCCHm (m = 0, 1, 2, 3) segments. Particularly encouraging theoretical predictions for HCCH and HCC segments were obtained for the COS-DEPT pulse sequence35 (not shown) with double the relative sensitivity (0.65) for HCCH segments and the same sensitivity (0.325) for HCC moieties. These results, however, were not confirmed experimentally by the authors. 

Thus, the 2D INADEQUATE spectrum of 2-chlorobutane confirms that the carbon of signal 1 is connected to the carbon of signal 3,3 is connected to 4, and 4 is connected to 2. Since the DEPT spectrum (or HET2DJ) of 2-chlorobutane already identified signals 1 and 2 as methyls, 3 as a methylene, and 4... 

COSY and a C.H-HSC. With only an edited DEPT spectrum and a 2D INADEQUATE spectrum the atomic sequence (structure without stereochemistry) of most molecules can be determined. However, there is a down side the time and effort required to generate the 2D INADEQUATE spectrum. Because we are looking at very weak sidebands of weak signals, it can take days of pulse sequence repetitions to generate the desired information. Moreover, the recycle delay between pulses must be carefully set to exceed (by 1.5- to 3-fold) the longest carbon T, value in the molecule. Also, the experiment... 

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