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Structure - activity relationship studies were performed on these compounds , and various modifications were made to their structures involving relocation of the halogen atom , introduction of more halogen atoms , replacement of the halogen with another group , replacement of the methylene linker with a difluoromethylene linker , replacement of the para - cyanophenyl ring with other ring structures , and replacement of the triazolyl group with an imidazolyl group .
 Chemical: halogen; Chemical: halogen; Chemical: halogen; Chemical: methylene; Chemical: difluoromethylene; Chemical: para - cyanophenyl; Chemical: triazolyl; Chemical: imidazolyl
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: halogen; Chemical: halogen; Chemical: halogen; Chemical: methylene; Chemical: difluoromethylene; Chemical: para - cyanophenyl; Chemical: triazolyl; Chemical: imidazolyl