Proton chemical shift values Appendix

XH chemical shifts. More detailed chemical shift data for a wide range of proton environments is given in Appendix 3, Tables A3.1, A3.3 and A3.4. In particular the chemical shift values quoted in Table A3.1 show that an electronegative substituent in aliphatic systems causes a downfield shift the greater the electronegativity the more substantial the shift. When two substituents are attached to the same carbon atom there is a greater downfield shift, but not as great as the sum of the two substituents separately. The approximate position of absorption in such cases can be predicted on the basis of the empirical parameters shown in Appendix 3, Table A 3.2. 

Approximate values of ehemieal shifts for different kinds of protons are shown in Table 14.1. (A more extensive compilation of chemical shifts is given in Appendix VI.) An NMR spectrum can be divided into six regions. Rather than memorizing chemical shift values, if you remember the kinds of protons that are in each region, you will be able to tell what kinds of protons a molecule has from a quick look at its NMR spectrum. 

Since chemical shift increments are approximately additive, it is possible to calculate the ring proton shifts in polysubstituted benzene rings from the monosubstituted values in Appendix Chart D.l. The chemical shift increments for the ring protons of m-diacetylbenzene ... 

Since the chemical shift of a proton is determined by its environment, we can construct a table of approximate chemical shifts for many types of compounds. Let s begin with a short table of representative chemical shifts (Table 13-3) and consider the reasons for some of the more interesting and unusual values. A comprehensive table of chemical shifts appears in Appendix 1. 

While attempting to establish the existence and role of the CTC in alternating copolymerizations, many authors have determined the equilibrium constant K) for a large number of MA-comonomer pairs (table in appendix to this chapter). Other charge-transfer complexes of MA have also been extensively investigated,by the use of ultravioletand spectroscopic methods (table in appendix to this chapter). Identification of the CTC is centered on the concentration and temperature dependence of the absorption in the visible and ultraviolet spectra. In NMR, the acceptor or donor protons undergo a chemical shift when the CTC is formed and this variation is used to determine the K values. Calorimetric methods have also been used to determine equilibrium constants. 

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