Stereoisomerism. 161 



This on treatment with potassium cyanide yielded 



CH 2 -(OH)-CH 2 (CN) 

 which on hydrolysis yielded 



CH 2 (OH)-CH 2 -COOH 



This was identical with neither sarcolactic acid nor with 

 the acid from sour milk, which latter can be synthetically 

 obtained by the action of dilute alkalis or silver hydroxide 

 on a-brompropionic acid 



CH 3 CHBr-COOH4-H 2 = CH 3 -CH(OH) COOH 

 (The alkali is omitted from this equation.) There were 

 therefore three isomeric acids obtained, all of which were 

 found to contain a hydroxyl and a carboxyl group. On 

 the basis of the formulae already discussed, only two 

 such isomerides are possible, namely, the a and /3 hydroxy 

 propionic acids 



CH 3 CH 2 (OH) 



I I 



CH(OH) and CH 2 



I I 



COOH COOH 



It was further shown that one of the three known 

 acids was optically active. (The explanation of "optical 

 activity " is given below.) These facts indicated to Wis- 

 licenus that the structural formulae hitherto in use were 

 not sufficient to explain all cases of isomerism. 



The second classical example which indicated the in- 

 sufficiency of structural formulas was that of the tartaric 

 acids. 



The aqueous solution of ordinary tartaric acid was 

 known to have the property of rotating the plane of 

 polarized light, but in 1830 Berzelius discovered in the 

 mother liquors from Kastner's tartaric acid manufactory 

 a second acid, very similar in its chemical properties, but 

 differing from ordinary tartaric acid in the fact that it 



(1,997) 11 



