146 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



and Groh have performed experiments with #-amino acids and /3-oxy 

 acids and have observed : 



HNO 2 



d-/8-amino-/8-phenylpropionic acid > l-j8-oxy--phenylpropionic acid 



HNO 2 



d-/8-amino-/8-phenylpropionic acid ester > l--oxy-|8-phenylpropionic acid ester. 



HNO 2 



d-0-aminobutyric acid > l--oxybutyric acid 



HNO 2 



d-/8-aminobutyric acid ester > 1-0-oxybutyric acid ester 



PC1 5 Ag2O 



l-/3-oxy butyric acid > d-|8-chlorbutyric acid > l-/3-oxybutyric acid 



PC1 6 AgaO 



l-j8-oxybutyric acid ester > d-0-chlorbutyric acid ester ^ l-/3-oxy butyric acid 



and 



hydrolysis 

 NOC1 

 d-j8-aminobutyric acid > l-/8-chlorbutyric acid > d--oxybutyric acid 



No change occurs with nitrous acid nor with phosphorus penta- 

 chloride, as the same product is obtained both with the ester and the 

 free acid ; d-/-aminobutyric acid has therefore the same configuration 

 as l-/3-oxybutyric acid. Since d--oxy butyric acid is formed from d-- 

 aminobutyric acid a Walden inversion has been produced by the action 

 of nitrosylchloride. The result is the same as with the a-amino 

 acids. 



Reviewing the data in 1911 Fischer stated that he thought that the 

 "Walden inversion" was not of the nature of a rearrangement of the 

 groups attached to the carbon atom, but that it was simply the general 

 and normal process of substitution which could be observed on account 

 of the asymmetry of the carbon atom in these cases. 



Adopting Werner's view that it was not necessary for the new group 

 to take up the same position as the old group but that it may take up 

 a different position, and regarding the process of substitution as if it 

 were preceded by the formation of complex molecules, as Kekule sug- 

 gested, then during the reaction of the complex molecule the new group 

 may take up a different position to that held by the old group. If in 

 the reaction the shifting take place in every molecule or does not 

 take place at all, then the new compound will have only one configuration ; 

 if, however, there be only a partial shifting, then a mixture will result. 

 In the case of optically active compounds we shall have either the one 

 isomer, or the other, or a mixture which represents the racemic form. 

 As racemisation always occurs in the " Walden inversion " this hypo- 

 thesis gives a good explanation of the observed phenomena. The 

 reaction is very easy to follow with a model such as Fischer used to 

 represent his views, but they may also be represented on a plane surface. 



