In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The synthesis and preliminary pharmacological evaluation of a series of potential atypical antipsychotic agents based on the structure of 1 - ( 1 , 2 - dihydro - 2 - acenaphthylenyl ) piperazine ( 7 ) is described .
### Output Text:
The synthesis and preliminary pharmacological evaluation of a series of potential atypical antipsychotic agents based on the structure of <span class="chemical">1 - ( 1 , 2 - dihydro - 2 - acenaphthylenyl ) piperazine</span> ( 7 ) is described . 