DEPT 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...

Of the multitude of ID 13C NMR experiments that can be performed, the two most common experiments are a simple broadband proton-decoupled 13C reference spectrum, and a distortionless enhancement polarization transfer (DEPT) sequence of experiments [29]. The latter, through addition and subtraction of data subsets, allows the presentation of the data as a series of edited experiments containing only methine, methylene and methyl resonances as separate subspectra. Quaternary carbons are excluded in the DEPT experiment and can only be observed in the 13C reference spectrum or by using another editing sequence such as APT [30]. The individual DEPT subspectra for CH, CH2 and CH3 resonances of santonin (4) are presented in Fig. 10.9. 

The DEPT spectrum of ipsenol is shown in Figure 4.12. It consists of the main spectrum (a), which is a standard -decoupled 13C spectrum the middle spectrum (b) is a DEPT 135 where the CH3 s and CH s are phased up, whereas the CH2 s are phased down. The top spectrum (c) is a DEPT 90, where only CH carbons are detected. Quaternary 13C are not detected in the DEPT subspectra. We can now interpret the 13C peaks in the main spectrum as CH3, CH2, CH, or C by examining the two subspectra peaks along with the main spectrum. The easiest way to approach the interpretation of the 13C/DEPT spectra... 

The 13C spectrum is unequivocal. It shows two peaks in the range for alkyne carbons. The peak at 70 ppm is about the same height as the two CH2 peaks, but the peak at about 81.2 ppm is distinctly less intense, indicating that it has no attached proton. Furthermore, the 13C/DEPT subspectra show that the peak at about 70 ppm represents a CH group. We can now write two fragments or substructures ... 

There are six different kinds of protons in the 1H spectrum in the ratios, from left to right, 1 2 1 2 3 3 with the total of 12 protons. We now count eight peaks in the 13C spectrum (assuming one carbon atom per peak), and from the 13C/DEPT subspectra we read (from left) (C=0) (from IR), CH, CH, CH, CH, CH2, CH3, CH3. With the present information, we write C8H120 with unit mass 124, which is 16 units less than then a molecular ion peak at mlz 140. Is there another oxygen atom in the molecular ion ... 

This process for separating the various DEPT subspectra by arithmetic manipulation of data resulting from different 0 values is referred to as editing. The edited DEPT spectra of the molecule below (artemisinin) are shown in Figure 12.17 ... 

The given structure A is confirmed by interpretation of the CH COSY and CH COLOC diagrams. All of the essential bonds of the decalin structure are derived from the correlation signals of the methyl protons. In this, the DEPT subspectra differentiate between the tetrahedral C atoms which... 

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