29917
First , several important theoretical concepts ( physical versus formal oxidation states , orbital interactions , use of ( spin ) natural and corresponding orbitals , exchange enhanced reactivity and the connection between valence bond and molecular orbital based electronic structure analysis ) are presented .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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