Signal shielding

For all the derivatives 10-13, the most shielded signal is close to 280 ppm, with the exception of 11(1) and to a lesser extent of 13(1). Such values aUow, by comparison with previous data, to assign this signal to the oxygen bound to the annular unsubstituted... 

The NMR spectrum of quinazoline in [ Hj,]DMSO shows two sharp signals at 97.8 (Nl) and 86.5 (N3) ppm with respect to external neat nitromethane. This assignment is in accordance with INDO/S-SOS shielding calculations. The more-shielded signal in the proton-coupled spectrum has a doublet splitting of 13.8 Hz, whereas the less-shielded signal has a multiplet structure. 

FIG. 1 Diamagnetic shielding signal against temperature for the sample of KjCeo used in the detailed X-ray study. 

The ability to fabricate circuits with a high number of layers allows for virtually unlimited groxmd planes, power planes, and shielded signal planes, all of which contribute to improved performance at high frequencies. 

The NMR spectrum in Figure 15.5 shows that the chemical shift (S) of the methyl protons is at 1.05 ppm and the chemical shift of the methylene protons, which are deshielded by the electron-withdrawing bromine, is at 3.28 ppna. Notice that low-frequency (shielded) signals have small d (ppm) values, whereas high-frequency (deshielded) signals have large d values. 

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