Integration and NMR peak area

Initiation step, 149, 153-154, 221, 246 Initiators of free-radical reactions, 220-221, 245-246, 415 16 Insulin, 1070, 1073-1074, 1080 Integration and NMR peak area measurement, 497... 

The overall blending stability of SMA in the material bulk and the surface grafting stability on material surfaces were examined by leaching tests and evaluated respectively with proton nuclear magnetic resonance spectroscopy [ H-NMR] and quantitative ATR-FT-IR. Firstly, SMA-MSPEO and SPEO with equivalent amounts of PEG components were respectively blended into PEU matrix materials. The initial quantity of PEG was measured and recorded by integrating the PEG-specific I-NMR peak areas at S = 3.52 ppm (- O - CH2 - CH2 - 0 -). The integral values were normalized... 

The release characteristics of 2-undecanone insect repellant from its a-CD-IC were studied using TGA either at a heating rate of 20°C/min in nitrogen and air atmospheres or at constant temperatures of 25 and 40°C over a period of 24 h (see Fig. 25). By integrating and comparing the areas of resonance peaks contributed by 2-undecanone and a-CD in the ll NMR spectrum of 2-undecanone-a-CD-IC, it was found that a-CD forms a 2 1 inclusion complex with 2-undecanone. This translates to 8 wt% 2-undecanone and 92 wt% a-CD in the stoichiometric 2-undecanone-a-CD-IC, which can be used to analyze TGA results to determine 2-undecanone weight loss. 

To obtain a H NMR (or proton NMR) spectrum, a small amount of sample is usually dissolved in a deuterated solvent (e.g. CDC13), and this is placed within a powerful magnetic field. The spectrum can provide information on the number of equivalent protons in an organic molecule. Equivalent protons show a single absorption, while non-equivalent protons give rise to separate absorptions. The number of peaks in the spectrum can therefore be used to determine how many different kinds of proton are present. The relative number of hydrogen atoms responsible for the peaks in the H NMR spectrum can be determined by integration of the peak areas. 

Problem 13.18 How many peaks would you expect in the H NMR spectrum of 1,4-dimethyl-benzene (pom-xylene, or p-xylene) What ratio of peak areas would you expect on integration of the spectrum Refer to Table 13.3 for approximate chemical shifts, and sketch what the spectrum would look like. (Remember from Section 2.4 that aromatic rings have two resonance forms.)... 

The Md NMR spectrum of /)-bromotoluene, shown in Figure 15.15, displays many of the features just discussed. The aromatic protons appear as two doublets at 7.02 and 7.45 8, and the benzylic methyl protons absorb as a sharp singlet at 2.29 8. Integration of the spectrum shows the expected 2 2 3 ratio of peak areas. 

An example of determination of dimethyl sulphoxide (in solutions and ointments) was given by Kram and Turczan124. They recorded the NMR spectra at 60 MHz of the sulphoxide in methanol + water or chloroform and integrated the peaks the amount of sulphoxide was calculated from the ratio of its peak area to that of methanol. 

NMR spectroscopy is a quantitative technique and NMR spectra are usually recorded with an integral which indicates the relative areas of the absorption peaks in the spectrum. The area of a peak is proportional to the number of protons which give rise to the signal. In most NMR spectrometers, the integral is represented as a horizontal line plotted over the spectrum. Whenever a peak is encountered, the vertical displacement of the integral line is proportional to the area of the peak. 

The functionality of the star was calculated by comparing the integrated peak area of core protons [aromatic (6=6.8 ppm), -CH2- (6=4.0 ppm)] to the chain end protons (-CH2- (6=1.95 ppm), and -CH3 (6=1.65 ppm)). This procedure gave -8.1 arms per core after correcting for the presence of -10% linear contaminant. Thus NMR spectroscopy provides direct evidence for the formation of... 

Peak Areas The areas of 13C NMR peaks are not necessarily proportional to the number of carbons giving rise to the peaks. Carbon atoms with two or three protons attached usually give the strongest absorptions, and carbons with no protons tend to give weak absorptions. Newer spectrometers have an integrating mode that uses decoupling techniques to equalize the absorptions of different carbon atoms. This mode makes peak integrals nearly proportional to the relative numbers of carbon atoms. 

---