Difference-spectrometry

The utility of NOE difference spectrometry for stereochemical problems is demonstrated. 

The same report that clarified the structures of the calafatine A -oxides (Section II,C,10) also described berbibuxine (87), C38H42N207, amorphous, [8]D -228° (c 0.19, CHC13). Diazomethane converted the alkaloid to calafatine (88, Section II,C,9). The location of the phenolic function was revealed by an NOE difference spectrometry (NOEDS) study (54, see Section VI,A,2,b). 

NUCLEAR OVERHAUSER EFFECT, DIFFERENCE SPECTROMETRY, H H PROXIMITY THROUGH SPACE 1 73... 

FIGURE 3.60 NOE difference spectrometry for compound III. a shows the H NMR spectrum, b shows enhancement of the H-4 proton on irradiation of the 3-methyl group, c shows enhancement of both protons on irradiation of the 5-methyl group. 300 MHz in CDCl3. 

NOE difference spectrometry determined the substitution pattern of a natural product, whose structure was either I or II. The readily available dimethyl homologue III was submitted to NOE difference spectrometry (Figure 3.60). 

Distinguishing between a trisubstituted ( )- and a (Z)-double bond is not a trivial assignment. The use of NOE difference spectrometry for this purpose is illustrated in Problem 7.4. 

There are still two remaining tasks assignment of stereochemistry of the C-2, C-3-double bond and assignment of the C-8 and C-9 methyl groups. NOE difference spectrometry is described in Section 3.16. It is a 1-D experiment that reveals H— H proximity through space because of enhancement by the nuclear Over-hauser effect. The difference spectrum is obtained by subtracting a standard H spectrum from the NOE spectrum this leaves only the enhanced peak(s). 

The application of infrared difference spectrometry to the measurement of protein adsorption at solid/liquid interfaces is potentially... 

Nuclear Overhauser Effect Difference Spectrometry, H H Proximity Through Space 189... 

NOE difference spectrometry is described in Section 4.20. It is a 1-D experiment that determines JH—JH proximity through space. The difference spectrum is obtained by subtracting a standard H spec-... 

The ATR method makes it possible to measure infrared spectra from the layer of the order of up to a few micrometers below a surface but it is also possible to extract information on a thinner layer by combining it with the method of difference spectrometry (see Section 6.2.3) in other words, the ATR method can be applied to more surface specific analysis. Figure 13.14a shows the ATR spectrum of polyethylene terephthalate (PET) covered with 0.05 pm-thick film of another material. The ATR spectrum of PET itself is shown in Figure 13.14b and the absorbance difference spectrum obtained by subtracting the spectrum in (b) from that in (a) is shown in Figure 13.14c. This spectrum is mostly due to the thin film covering the PET, and it is inferred from this spectrum that this surface-layer film is made of some kind of polyurethane. 

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