Hydrogen splitting

The 31P NMR spectrum of RhH2Cl(PBu2)2 is shown in Figure 2.69 the triplets show coupling with two equivalent hydrogens, split further by coupling with rhodium (/(Rh-P) 110.3 Hz /(P-H) 14.9 Hz). 

A fuel cell uses the reverse process. Hydrogen along with oxygen from the air are applied to the cell. The hydrogen splits to release its electrons to the external circuit and provide power to the load. The protons move across the membrane, attracted by the oxygen potential, and combine with the oxygen to form water at the opposite electrode surface. 

The lines in the spectrum of Fig. 1 are, even under optimum experimental conditions, quite broad. This is due to small unresolved hyperfine interaction with the eighteen equivalent hydrogen atoms. Either the width of the lines, or nmr measurements (La Mar et al., 1973) can reveal the magnitude of this y-hydrogen splitting (ca. 0.15 G—dependent on temperature and solvent). 

Resolvable long-range splitting, particularly from y-hydrogen, are not uncommon, and can be invaluable in structure elucidation. Like the -hydrogen splittings, these are conformation-dependent, but only exceptionally, in relatively rigid cyclic nitroxides, do they exceed ca. 0.5 G. 

The first term in the rate expression, which is pH-independent, apparently corresponds to a reaction path in which hydrogen splits homoly-tically, i.e.. 

Catalytic species Solvent Temp. range, °C. Kinetics of hydrogen activation Proposed mechanism of hydrogen splitting Refs. 

The abnormally large negative entropy of activation (—17 e.u.) suggests that one of the first two mechanisms of hydrogen splitting, rather than the last one, is correct. 

There are many examples where monohydridometal complexes are formed via homolytic or heterolytic hydrogen splitting.24 31 The basic difference between the... 

The error made in assigning the mechanism in the two computational studies should perhaps not be judged too harshly, as the hydrogen splitting step was never the main focus of attention. But it serves as a reminder of the point made in the previous section just like those based on experimental data, mechanisms derived from computational work can be very hard to prove. 

The ESR spectrum of the radical cation of 4 showed a hydrogen splitting over 10G, requiring that it is a significant twist of the N-N bond. Such data are coherent with the X-ray data but in disagreement with theoretical calculations... 

Diesters, diacid chlorides and dihaloalkanes react with suitable cyclic hydrazines to give saturated or partially unsaturated pyrazolo[l,2-a]pyridazines (62HCA37). For example, tetrahydropyrazole and diethyl succinate give the dione (218) which under standard amide reduction conditions gives (219 Scheme 66). As with most saturated pyrazolo[l,2-a]-pyridazines, catalytic hydrogenation splits the N—N bond of (219) (72JHC41). 

In aprotic solvents diketones can be produced exclusively. This indicates that palladium hydrides, generated via water-gas shift reaction (eq. (9)), or by hetero-lytic hydrogen splitting (eq. (10)), are indeed efficient initiators and it also shows that protonolysis and/or hydrogenolysis of palladium alkyls can be an efficient termination mechanism. 

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