The Oxygen Molecule

According to molecular orbital theory the valence p-orbitals of the oxygen atoms combine to form three bonding and three antibonding orbitals in molecular oxygen, as shown in Fig. 1. 

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The presence of oxygen can modify the course of a fiee-radical chain reaction if a radical intermediate is diverted by reaction with molecular oxygen. The oxygen molecule, with its two unpaired electrons, is extremely reactive toward most free-radical intermediates. The product which is formed is a reactive peroxyl radical, which can propagate a chain reaction leading to oxygen-containing products. 

Regarding AS, the simplest assumption we can make is that it comes entirely from the loss of translational and rotational degrees of freedom of the oxygen molecule when it is absorbed into the crystal. A standard calculation then gives (the electronic ground state of O2 is a triplet)... 

The oxygen molecule carries out molecular vibration at a frequency of 2.4 X 1013 cydes/sec-ond. If the pressure is such that an oxygen molecule has about 109 collisions per second, how many times does the molecule vibrate between collisions ... 

Now let us investigate the oxygen molecule, which experiment tells us has the molecular formula O2. We might begin by considering formation of a single bond between two oxygen atoms, as represented by the orbital representation... 

Nuclear magnetic resonance spectroscopy of the solutes in clathrates and low temperature specific heat measurements are thought to be particularly promising methods for providing more detailed information on the rotational freedom of the solute molecules and their interaction with the host lattice. The absence of electron paramagnetic resonance of the oxygen molecule in a hydroquinone clathrate has already been explained on the basis of weak orientational effects by Meyer, O Brien, and van Vleck.18... 

Moffitt, W., Proc. Roy. Soc. London) A210, 224, The electronic structure of the oxygen molecule. ... 

Fumi, F. G., and Parr, R. G., /. Chew. Phys. 21, 1864, Electronic states of diatomic molecules The oxygen molecule. ... 

FIGURE 19.20 One of the four polypeptide chains that make up the human hemoglobin molecule. The chains consist of alternating regions of a helix and p sheet. The a-helix regions are represented by red helices. The oxygen molecules that we inhale attach to the iron atom (blue sphere) and are curried through the bloodstream. 

The state of the oxygen molecule, 1.62 v. e. above the normal state, probably corresponds to a double bond between the two atoms. This gives 3.47 v. e. for 0 0. 

Illuminated chlorophyll molecules can form excitation states which are able to transfer energy on to the oxygen molecule, raising it from its ground state to the more reactive excited state known as singlet oxygen. 

At mercury and graphite electrodes the kinetics of reactions (15.21) and (15.22) can be studied separately (in different regions of potential). It follows from the experimental data (Fig. 15.6) that in acidic solutions the slope b 0.12 V. The reaction rate is proportional to the oxygen partial pressure (its solution concentration). At a given current density the electrode potential is independent of solution pH because of the shift of equilibrium potential, the electrode s polarization decreases by 0.06 V when the pH is raised by a unit. These data indicate that the rate-determining step is addition of the first electron to the oxygen molecule ... 

Why do hydrogen and oxygen require a spark before they will react To react with one another, the oxygen molecule O2 and... 

In principle, a total of 4 electrons may be progressively added to the oxygen molecule, eventually resulting in zero bond order — hence the ultimate reduction product is oxide. 

The metal ion, e.g. Fe or Co, when in its lower oxidation state can share electron charge with the oxygen molecule adduct. Several iron and cobalt prophyrin derivatives and cobalt-Schiff bases show the necessary reversibility and rates for successful application [e.g. 23]. a, a, a", a" -weso-tetrakis[(o-piralamidophenyl)-po phinato] Co (II) has been complexed with 1-methylimidazole to make a complex (CoPIm) which, when mixed with polybutyl methacrylate gave oxygen permeabilities on the order of 10-9 sec-cm/(cm2-s-cmHg) with a selectivity of about 5 over nitrogen [23]. 

Linnett used the concept that an octet of valence shell electrons consists of two sets of four opposite-spin electrons to show that in diatomic and other linear molecules the two tetrahedra are not in general formed into four pairs as we have discussed for F2 and the CC triple bond in C2H2. This idea is the basis of the double-quartet model, which Linnett applied to describe the bonding in a variety of molecules. It is particularly useful for the description of the bonding in radicals, including in particular the oxygen molecule, which has two unpaired electrons and is therefore paramagnetic This unusual property is not explained by the Lewis structure... 

The oxygen molecule, a paramagnetic species with an unpaired electron on each atom, has already been referred to as biradical, albeit an unreactive one. The photochemical excitation of an anthracene to a biradical, or to something rather like one, has also been mentioned (p. 331) if this excitation is carried out in the absence of air or oxygen, instead of the trans-annular peroxide—(104)—a photo-dimer (130) is obtained ... 

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