14688
Compounds 1 , 2 and 9 possessed 2 - methylbutyric acid in their molecules , the absolute configuration of which was found to be 2S by comparison of its HPLC behavior with that of an authentic sample .
 2 - methylbutyric acid
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 2 - methylbutyric acid