ALTADENA and PASADENA

It is still rather difficult to exactly reproduce an experimentally obtained ALTADENA spectrum via a simulation. This is because the supplemental processes, which cause a spreading of the polarization across the whole spin system of the product molecule, are difficult to determine or to even guess correctly. The method is, therefore, most suitable and most efficient for cases where qualitative results are sufficient. 

For all the reasons mentioned above, it is more desirable to obtain PASADENA spectra when applying the PHIP method, at least initially. Nevertheless, in certain cases ALTADENA spectra can be very helpful, too, especially for a quick screening, because these experiments can be performed without any specialized NMR probes. Rather, in these cases, standard NMR equipment will suffice totally. Furthermore, in other cases, the (normally unwanted) isotropic mixing can be used advantageously to obtain information about other additional aspects of the system. A typical such case results when it is desirable to transfer the original proton polar- 

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Fig. 12.4 Normal NMR, high-field (PASADENA) and low-field (ALTADENA) PHIP.

Figure 9.11 The difference between PASADENA- and AtTADENA-PHIP-NMR spectra hydrogenation of diphenylbutadiene. (a) PASADENA spectrum, (b) ALTADENA spectrum [38].

As mentioned above, PHIP is a versatile tool for the study of catalytic reactions. In the following three different experimental examples of this remarkable power, taken from recent work from the Bargon group followed by a theoretical example of reaction pathway sensitivity from our group are given. The experimental examples show a PHIP experiment performed under ALTADENA conditions, a PHIP experiment performed under PASADENA conditions and a PHIP experiment followed by a heteronuclear polarisation transfer from H to i C. 

Supported metal catalysts can produce PHIP effects in liquid-phase hydrogenations as well, as was demonstrated successfully in several publications [15, 126, 127]. Bubbling of a mixture of propylene and pH2 through an NMR tube with a solvent (toluene, acetone) and solid catalyst (Rh/Ti02 or Rh/AlO(OH)) produced PHIP effects for the dissolved reaction product propane in both PASADENA and ALTADENA experiments [15,126]. The same two supported metal catalysts were used in the hydrogenation of styrene into ethylbenzene in acetone-d6, producing... 

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