Hydrogen ions Protons

Electrophile Addition Reactions. The addition of electrophilic (acidic) reagents HZ to propylene involves two steps. The first is the slow transfer of the hydrogen ion (proton) from one base to another, ie, from Z to the propylene double bond, to form a carbocation. The second is a rapid combination of the carbocation with the base, Z . The electrophile is not necessarily limited to a Lowry-Briiinsted acid, which has a proton to transfer, but can be any electron-deficient molecule (Lewis acid). 

ACID A chemical compound whose aqueous solution turns blue litmus paper red, reacts with and dissolves certain metals to form salts, and reacts with bases to produce salts and water. They are capable of transfeiTing a hydrogen ion (proton) in solution. 

Bronsted-Lowry acid (Section 2.7) A substance that donates a hydrogen ion (proton H + ) to a base. 

Mitchell s chemiosmotic theory postulates that the energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane. The electrochemical potential difference resulting from the asymmetric dis-... 

At the anode, a platinum catalyst causes the hydrogen to split into positively charged hydrogen ions (protons) and negatively charged electrons. 

J. N. Bronsted and T. M. Lowry independently arrived at definitions of an acid and a base that do not involve water. They recognized that the essential characteristic of an acid-base reaction was the transfer of a hydrogen ion (proton) from one species (the acid) to another (the base). According to these definitions, an acid is a proton donor and a base is a proton acceptor. The proton must be donated to some other species so there is no acid without a base. According to Arrhenius, HC1 is an acid because... 

Ammonium and hydrogen ions (protons) are both present in the soil solution as multielement cations. Ammonia gas reacts with water to produce the ammonium cation, NH4+ (Figure 5.8, equation 1). Ammonium acts as a cation in all senses and will be attracted to cation exchange sites on soil particles. Ammonium in the soil solution and on exchange sites is available to plants. 

On the hydrogen side of the membrane, a hydrogen molecule with two hydrogen atoms will attach itself to two adjacent catalyst sites. This frees positive hydrogen ions (protons) to travel across the membrane. 

We consider, as an example, a gaseous hydrogen ion (proton) in the standard state, whidi is at the reference zero of proton level. The ionization of gaseous hydrogen molecule in the standard state to produce a standard gaseous proton is shown in Eqn. 3-47 ... 

In general, acids are defined as substances that can donate hydrogen ions (protons), while bases are compounds that accept protons. 

Still higher total conductivities are achievable in a special class of hydrogen-ion (proton)-conducting polymers. These polymers are particularly useful for fuel-cell and chlor-alkaU processing applications in which the efficient transfer of protons is critical. These polymers are of produced in membrane form and are therefore referred to as proton-exchange membranes (PEM). 

LEWIS ACID. Any molecule or ion (culled and electrophilel that can combine with another molecule or ion by lomtiog a covalent bond with two electrons I rum the second molecule or ion. An acid is thus an electron acceptor. Hydrogen ion (proton) is the simplest substance that will do ihis. but many compounds such as boron trilluuricJe. Bt . nod aluminum chloride. AlCIv. exhibit the same behavior and are therefore properly called adds. Such substances show acid effects on indicator colors and when dissolved in the proper solvents. 

The hydrogen oxidation within a fuel cell occurs partly at the anode and the cathode. Different models were supposed for the detailed reaction mechanisms of the hydrogen at Ni-YSZ (yttria stabilised zirconia) cermet anodes. The major differences of the models were found with regard to the location where the chemical and electrochemical reactions occur at the TPB (three-phase boundary of the gaseous phase, the electrode and the electrolyte). However, it is assumed that the hydrogen is adsorbed at the anode, ionised and the electrons are used within an external electrical circuit to convert the electrical potential between the anode and the cathode into work. Oxygen is adsorbed at the cathode and ionised by the electrons of the load. The electrolyte leads the oxide ion from the cathode to the anode. The hydrogen ions (protons) and the oxide ion form a molecule of water. The anodic reaction is... 

The mechanism of aromatic nitration is shown in Figure 1. It may be seen that the sulfuric acid serves as the source of hydrogen ion (proton) which protonates nitric acid to form nitronium ion and water. The NO, ion is the active electrophile that causes the nitration reactions. 

These radionuclides are produced by irradiating targets with beams of hydrogen ions (protons), but frequently deuterium ions (deuterons) are used (see Table 21.10). Some products require beams of helium-4 and helium-3 ions. The typical process involves the capture of the proton with the prompt emission of a neutron. This is called a p,n reaction. However, in other cases there may be protons, alpha particles, or up to five neutrons emitted. The resulting products decay generally by positively charged electron (positron) emission, but also decay by capture of an orbital electron. 

A PEM electrolyzer is literally a PEM fuel cell operating in reverse mode. When water is introduced to the PEM electrolyzer cell, hydrogen ions (protons) are drawn into and through the membrane, where they recombine with electrons to form hydrogen molecules. Oxygen gas remains behind in the water. As this water is recirculated, oxygen accumulates in a separation tank and can then be removed from the system. Hydrogen gas is separately channeled from the cell stack and captured. 

Actually, hydrogen ions (protons) do not exist in aqueous solutions. Each proton combines with one water molecule by coordination with a free pair of electrons on the oxygen of water, and hydronium ions are formed ... 

Phosphonium salts containing a P—H bond form in condensed phases upon strong-acid protonation or in the gas phase by hydrogen-ion protonation of phosphines ... 

The most common isotope of hydrogen, H, has no neutrons. Thus, H+ is a bare proton. In discussions of acids and bases, we use the terms hydrogen ion, proton, and H interchangeably. 

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