Properties of Molecular Oxygen

For the purposes of this review we shall reserve the term molecular oxygen for free gaseous O2 in cases where the O2 entity is bound to other atoms we shall use the term dioxygen. This is a structural definition which requires only the continued existence of O-O bonding in the complex molecule, and gives no information on the bonding of the O2 species. 

The electronic structure of molecular oxygen in its ground state is well known (Fig. 1). The two lowest excited states of molecular oxygen, the Ag and 2g are obtained by pairing the spins of the two electrons in the Jtg orbital, and lie respectively at 94.2 and 156.9 kJ/mol above the ground state 

The triplet ground state of molecular oxygen provides a considerable kinetic barrier to the auto-oxidation of normally diamagnetic organic molecules where reactions involving change of spin are generally very slow, and where products formed in triplet states are unstable. This barrier may be circumvented in three ways  

The ions arising from simple one electron reductions or oxidations of molecular oxygen are well characterised and their properties summarised in Table 1. 

The possible importance of partially reduced dioxygen species in biochemical reactions has led to a reinvestigation of their equilibria in aqueous solutions and the values obtained are summarised in Table 2. 

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A number of magnetic properties have been calculated inter alia in a MCSCF study of the ground state properties of molecular oxygen by Minaev.23... 

However, this conflicts with other evidence that the oxygen atoms are connected by something other than a single bond. In essence, it is impossible to write a single Lewis diagram that satisfactorily explains all the properties of molecular oxygen. 

If one were to try to draw the simplest Lewis structure for molecular oxygen, the result might be the following 0=Q ). However, it is known from the properties of molecular oxygen and experiments that O2 contains two... 

Castor oil (qv) contains a predominance of ricinoleic acid which has an unusual stmcture inasmuch as a double bond is present in the 9 position while a hydroxyl group occurs in the 12 position. The biochemical origin of ricinoleic acid [141-22-0] in the castor seed arises from enzymatic hydroxylation of oleoyl-CoA in the presence of molecular oxygen. The unusual stmcture of ricinoleic acid affects the solubiUty and physical properties of castor oil. 

The development of such a reaction proceeding under mild conditions is a technological challenge constituting one of the key points for the finalizing of efficient and low cost fuel cells. The catalytic properties of macrocyclic complexes like porphyrins and phthalocyanines for the reduction of molecular oxygen have been well known for four decades350,351 and numerous papers are devoted to this area. Here only some relevant and recent work in this field is described. 

Recent work in our laboratories has confirmed the existence of a similar pathway in the oxidation of vindoline in mammals (777). The availability of compounds such as 59 as analytical standards, along with published mass spectral and NMR spectral properties of this compound, served to facilitate identification of metabolites formed in mammalian liver microsome incubations. Two compounds are produced during incubations with mouse liver microsome preparations 17-deacetylvindoline, and the dihydrovindoline ether dimer 59. Both compounds were isolated and completely characterized by spectral comparison to authentic standards. This work emphasizes the prospective value of microbial and enzymatic transformation studies in predicting pathways of metabolism in mammalian systems. This work would also suggest the involvement of cytochrome P-450 enzyme system(s) in the oxidation process. Whether the first steps involve direct introduction of molecular oxygen at position 3 of vindoline or an initial abstraction of electrons, as in Scheme 15, remains unknown. The establishment of a metabolic pathway in mammals, identical to those found in Strep-tomycetes, with copper oxidases and peroxidases again confirms the prospective value of the microbial models of mammalian metabolism concept. 

Molecular connectivity indices are desirable as potential explanatory variables because they can be calculated for a nominal cost (fractions of a second by computer) and they describe fundamental relationships about chemical structure. That Is, they describe how non-hydrogen atoms of a molecule are "connected". Here we are most concerned with the statistical properties of molecular connectivity Indices for a large set of chemicals In TSCA and the presentation of the results of multivariate analyses using these Indices as explanatory variables to understand several properties important to environmental chemists. We will focus on two properties for which we have a relatively large data base (1) biodegradation as measured by the percentage of theoretical 5-day biochemical oxygen demand (B0D)( 11), and (2) n-octanol/water partition coefficient or hereafter termed log P (12). 

The following are other recent reviews on the molecular and physical properties of this oxygen binding protein. 

Fullerene Ceo is an electron-deficient compound with rich photophysical and photochemical properties. Moreover, the triplet-excited state of Ceo is formed almost quantitatively and, in the presence of molecular oxygen, energy transfer from the triplet-excited... 

The properties of the low-lying singlet excited states of molecular oxygen are significantly different from those of the ground state. For example, both O A,) and 02(1S9+) can react at room temperature with ozone according to... 

By partial charge transfer from the catalyst to the oxygen, the latter obtains properties different from those of molecular oxygen and is chemically activated. This mechanism has often been proposed but has never actually been proven. 

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