6440
The barriers to internal rotation of the methyl groups were determined to be 1052 and 905 cm ( - 1 ) at the MP2 / 6 - 311 + + G ( d , p ) and the B3LYP / 6 - 311 + + G ( d , p ) levels , respectively .
 methyl
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 methyl