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  ANSWER 
Ch 12 contents
2-pentyne.   The acetylide ion has an electron rich C atom so it reacts as a nucleophile.  Tosylates are derivatives of alcohols used because the tosylate is a good leaving group.  The tosylate is electrophilic at the C-OTs carbon center and undergoes an SN2 reaction so forming a new C-C in the new internal alkyne : 

2-pentyne