LEONOR MICHAELIS 



such reactions as the conversion of benzene to cyclohexane, however, 

 it is recognized that one may prefer to use the term hydrogenation 

 instead of reduction. As regards the chain of oxidation reactions as 

 they occur in respiration, it is often said that hydrogen atoms are 

 transferred from one molecular species to another. However, the 

 oxidation of reduced cytochrome to cytochrome involves not the 

 transfer of a whole hydrogen atom, but of one electron only. It is 

 therefore not entirely true that the chain of respiratory processes con- 

 sists in transferring hydrogen atoms from one molecular species to 

 another, and finally to oxygen, but it is true that this chain consists 

 in transferring electrons from one molecular species to another. Some- 

 times the transfer of the electron is accompanied by a transfer of a 

 proton and sometimes it is not. 



It may be added that the loss of a hydrogen atom in dehydro- 

 genation is equivalent to the addition of a hydroxyl group, as far as 

 the level of oxidation-reduction is concerned. When alcohol is oxi- 

 dized to acetaldehyde, the process may be alternately described as 

 follows. Alcohol detaches one hydrogen atom and accepts a hydroxyl 

 group: 



/H /OH /O 



CHsC^OH > CH3C— OH > CHsC^OH > CHsC^^ + H2O 



\H \H \H \H 



Here, the first step is the detachment of the hydrogen atom, and the 

 second, attachment of the hydroxyl group, while the process formerly 

 was described in terms of loss of two hydrogen atoms. So, a'^hydro- 

 genation is equivalent to "hydroxylation," and both terms can be 

 avoided by describing the level of oxidation proper only in terms of 

 electrons ejected or added, whether or not a proton or a hydroxyl ion 

 is also involved in the process. 



Stepwise Oxidation and Reduction of Organic Compounds 



If one wants to formulate a simple example of a possible step- 

 wise oxidation of an organic compound, one might propose the series: 



CH4 > CH3OH > CH2O > HCOOH > CO2 



each step representing a bivalent oxidation. A univalent oxidation is 

 not imaginable unless one abandons the a.ssumption that carbon is 



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