Nitropropanes, proton transfer from

The first clue is that the tunnel correction is sensitive to steric effects. Thus the isotope effect in the reaction of 2-nitropropane with pyridine or with 3,4-dimethylpyridine is hardly more than half that with 2,6-dimethylpyridine or 2,4,6-trimethylpyridine [15, 34, 35], and the fact that there is substantial steric hindrance is demonstrated by the deviation of these last two bases from the Bronsted plot they react too slowly by a factor of 5 [36, 37]. Since these first examples, there have been other examples of exaggerated isotope effects in sterically hindered proton transfers, and the evidence for tunnelling has been reinforced. 

Conventional kinetic analysis of the reactions of NM, nitroethane (NE), and 2-nitropropane (2-NP) with hydroxide ion in water revealed that the reactions are complex and involve kinetically significant intermediates. The deviations from first-order kinetics were observed to increase with increasing extent of reaction and in the reactant order NM < NE < 2-NP. The apparent deuterium kinetic isotope effects for proton/deuteron transfer approach unity near zero time and increase with time towards plateau values as the reaction kinetics reach steady state. 

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