Bronsted protons, motion

Cooperativity in the conduction of protons in hydrated PEMs encompasses effects including the mobility of protons via a flux of water molecules, the amphotericity (i.e. the ability to act as both a Lowry-Bronsted proton donor and acceptor) of the protogenic groups, and the motion of either the proto-genic group or side chain that facilitates the hand off or net transport of a proton. In this section we exclude our discussion to only the latter flexibility of the side chains of PFSA membranes. 

On a molar basis, most organic compounds contain similar amounts of hydrogen and carbon, and processes involving transfer of hydrogen between covalently bound sites rank in importance in organic chemistry second only to those involving the carbon-carbon bond itself. Most commonly, hydrogen is transferred as a proton between atoms with available electron pairs (l), i.e. Bronsted acid/base reactions. The alternative closed shell process, hydride transfer or shift, involves motion of a proton with a pair of electrons between electron deficient sites (2). These processes have four and two electrons respectively to distribute over the three atomic centres in their transition structures. It is the latter process, particularly when the heavy atoms are both first row elements, which is the subject of this review. The terms transfer and shift are used here only to differentiate intermolecu-lar and intramolecular reactions. 

Bronsted acid a substance that donates protons Bronsted base a substance that accepts protons Brownian motion random movement in suspensions caused by collisions with molecules... 

It is necessary, before proceeding to an investigation of the idea that Bronsted exponents measure transition state structure in a quantitative way, to formulate a fairly precise definition of degree of proton transfer. It would seem logical to use bond order for this purpose, and to set the degree of proton transfer equal to the order of the bond being formed between the proton in motion and the proton acceptor. 

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