5259
Although the interactions between K ( + ) and the fluorenone carbonyl group result in an average lengthening of the C [ double bond , length as m - dash ] O bond and in a redshift of the lowest energy absorption band compared to gas phase or non - polar solvents , the magnitude of this shift is noticeably smaller than the total shift .
 K ( + ), fluorenone carbonyl, C, O
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 K ( + ), fluorenone carbonyl, C, O