Subspectra

Conditions CDCI3, 25°C, 400 MHz H), 100 MHz ( C). (a,b) //NMR spectra, aromatic region (a), aliphatic region (b) (c) HH COSY plot of aliphatic shift range (d) CH COSY plot with DEPT subspectra to distinguish CH and CHy,... 

Part structure A is recognised to be a 2,5-disubstituted cyclohexa-1,3-diene on the basis of its chemical shift values. The ethyl group is one substituent, the other is a carboxy function judging by the chemical shift value of 8c = 174.1. The CH multiplicities which follow from the DEPT subspectra, 2C, 4CH, 5CH2 and CHj, lead to the CH part formula C2 + C4H4 + CsHw + CH3 = C12///7. Comparison with the given molecular formula, Ci2/7j 03, indicates an OH group. Since... 

Following the strategy applied in the previous problem, the correlation signals of the INADEQUATE experiment build up the methylcyclopentane skeleton A of the compound. DEPT subspectra c support the analysis of the CH multiplicities also resulting from the INADEQUATE plot which gives the number of CC bonds that radiate from each C atom. 

Table 54.1. Intepretation of the CH COSY and the CH COLOC plots and the DEPT subspectra...

The errors in the APT spectra may arise due to (a) variation in the relaxation times of different carbons, (b) wide variation in / h values, and (c) modulations caused by long range C- H couplings. A procedure known as ESCORT (Error Self Compensation Research by Tao Scrambling) has been developed to yield cleaner subspectra with reduced / cross-talk (Madsen et ai, 1986). This involves replacing the normal APT spectral... 

Suitable combinations of these spectra allow us to generate subspectra containing CH, CH2, or CHj carbons. 

Editing Obtaining a given set of subspectra to supply some desired information, e.g., the multiplicity of signals. 

Mbssbauer spectra can yield valuable information about the abundance of different Mbssbauer sites in a sample from the relative intensities of the corresponding subspectra if the/-factors are known. These, however, depend critically on temperature. Differences for the individual sites must be expected at ambient temperatures however, they all vanish at 4.2 K because f T) approaches one for T 0 (see (2.15)). Often measurements at 80 K are sufficient for reliable estimates of the true intensity ratio of Mbssbauer subspectra. 

Fig. 4.3 Ranges of isomer shifts observed for Fe compounds relative to metallic iron at room temperature (adapted from [24] and complemented with recent data). The high values above 1.4-2 mm s were obtained from Co emission experiments with insulators like NaCl, MgO or Ti02 [25-28], which yielded complex multi-component spectra. However, the assignment of subspectra for Fe(I) to Fe(III) in different spin states has never been confirmed by applied-field measurements, or other means. More recent examples of structurally characterized molecular Fe (I)-diketiminate and tris(phosphino)borate complexes with three-coordinate iron show values around 0.45-0.57 mm s [29-31]. The usual low-spin state for Fe(IV) with 3d configuration is 5 = 1 for quasi-octahedral or tetrahedral coordination. The low-low-spin state with S = 0 is found for distorted trigonal-prismatic sites with three strong ligands [30, 32]. Occurs only in ferrates. There is only one example of a molecular iron(VI) complex it is six-coordinate and has spin S = 0 [33]...

Because protein ROA spectra contain bands characteristic of loops and turns in addition to bands characteristic of secondary structure, they should provide information on the overall three-dimensional solution structure. We are developing a pattern recognition program, based on principal component analysis (PCA), to identify protein folds from ROA spectral band patterns (Blanch etal., 2002b). The method is similar to one developed for the determination of the structure of proteins from VCD (Pancoska etal., 1991) and UVCD (Venyaminov and Yang, 1996) spectra, but is expected to provide enhanced discrimination between different structural types since protein ROA spectra contain many more structure-sensitive bands than do either VCD or UVCD. From the ROA spectral data, the PCA program calculates a set of subspectra that serve as basis functions, the algebraic combination of which with appropriate expansion coefficients can be used to reconstruct any member of the... 

Figure 15 HMBC and broadband HMBC spectra of cyclosporine in C6D6 recorded with the pulse sequence shown in Figure 14. (A) HMBC spectrum recorded with A = 65.0 ms and 32 scans. (B) HMBC spectrum where two subspectra of 16 scans each recorded with A = 65.0 ms and 120 ms, and co-added in absolute-value mode. (C) broadband HMBC spectrum where four subspectra of eight scans each were recorded with A = 96.7, 84.4, 81.8, and 80.8 ms, respectively, and co-added in absolute-value mode.

Figure 16 u/tro-HMBC spectrum of cyclosporine in C6D6 recorded with the pulse sequence shown in Figure 14 where four subspectra of eight scans each were recorded with A = 181.1,160.0,115.0, and 99.3 ms, respectively, and co-added in absolute-value mode. 

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