Base protonation

Thermal decomposition of LiR eliminates a /6-hydrogen atom to give an olefin and LiH, a process of industrial importance for long-chain terminal alkenes. Alkenes can also be produced by treatment of ethers, the organometallic reacting here as a very strong base (proton acceptor) ... 

Reactions. The N atom in c vr7r>polyphospha-zenes can act as a weak Br0nsied base (proton acceptor) towards such strong acids a.s HF... 

On the Brpnsted theory (p. 51), solutions with concentrations of H3O+ greater than that in pure water are acids (proton donors), and solutions rich in OH are bases (proton acceptors). The same classifications follow from the solvent-system theory of acids and bases... 

In very strongly acidic nonaqueous solutions (such as HF/8bF5) H28 acts as a base (proton acceptor) and the white crystalline... 

Because water is amphiprotic—because it is both a Bronsted acid and a Bronsted base—proton transfer between water molecules occurs even in pure water, with one molecule acting as a proton donor and a neighboring molecule acting as a base ... 

Acid/base Proton donor H + proton acceptor... 

According to this theory, an acid is defined as a proton donor and a base as a proton acceptor (a base must have a pair of electrons available to share with the proton this is usually present as an unshared pair, but sometimes is in a 7t orbital). An acid-base reaction is simply the transfer of a proton from an acid to a base. (Protons do not exist free in solution but must be attached to an electron pair). When the acid gives up a proton, the species remaining still retains the electron pair to which the proton was formerly attached. Thus the new species, in theory at least, can reacquire a proton and is therefore a base. It is referred to as the conjugate base of the acid. All acids have a conjugate base, and all bases have a conjugate acid. All acid-base reactions fit the equation... 

Weak Bases Proton Transfer from Water... 

Because the breadth of chemical behavior can be bewildering in its complexity, chemists search for general ways to organize chemical reactivity patterns. Two familiar patterns are Br< )nsted acid-base (proton transfer) and oxidation-reduction (electron transfer) reactions. A related pattern of reactivity can be viewed as the donation of a pair of electrons to form a new bond. One example is the reaction between gaseous ammonia and trimethyl boron, in which the ammonia molecule uses its nonbonding pair of electrons to form a bond between nitrogen and boron ... 

C) The Bronsted-Lowry or proton theory interprets the acid-base reaction as a mere proton exchange between the acid (proton donor) and the base (proton acceptor) however, the Lewis theory or electron theory interprets the reaction as a donation and acceptance of a lone pair of electrons, where the... 

The chromophore, 11-ris-retinal, is linked to the a-amino group of lysine-296 in helix 7 via a protonated Schiff base. Protonated Schiff bases usually absorb light maximally at around 440 nm, but the of rhodopsin is near 500 nm. 

In the forward direction, HF is the acid, (proton donor forms IT), and H20 is the base (proton acceptor forms H30+). In the reverse direction F is the base (forms HF), accepting a proton from H30+, which is the acid, (forms H20). 

The acids (proton donors) and bases (proton acceptors) are labeled below their formulas. Remember that a proton, in Bransted-Lowry acid-base theory, is H+. 

According to Brpnsted-Lowry theory, a water molecule can accept a proton, thereby becoming a hydronium ion. In this case, water is acting as a base (proton acceptor). 

If only the acid/base proton dissociation of complex MOH is considered, Scheme 4 is simplified to include only steps (a) and (b) therein. According to this model, (I) is the primary deprotonation pathway in acidic medium, while (III) is of importance in basic media. On the other hand, direct proton transfer (II) can occur around neutral pH values. 

Before examining the equilibrium behavior of aqueous solutions of weak bases, let s look at the behavior of water itself. In the initial discussion of acid—base equilibrium above, we showed water acting both as an acid (proton donor when put with a base) and a base (proton acceptor when put with an acid). Water is amphoteric, it will act as either an acid or a base, depending on whether the other species is a base or acid. But in pure water the same amphoteric nature is noted. In pure water a very small amount of proton transfer is taking place ... 

Experimental Rate Constants for Base Protonation Illustrating the Influence of Ionic Charge on Protonation Reactions in Aqueous Solution (25 C, p = 0 M)... 

A. M. Schaffer and M. Gouterman, Porphyrins XXV. Extended Huckel calculations on location and specUal effects of free base protons, Theoret. Chim. Acta 25, 62-82 (1972). 

On the other hand, the general case for an organic base (proton acceptor) can be given as... 

Guo, Q., Pintauro, P. N., Tang, H. and O Cormor, S. 1999. Sulfonated and cross-linked polyphosphazene-based proton-exchange membranes. Journal of Membrane Science 154 175-181. 

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