Page numbers refer to Organic Chemistry third edition by Paula Yurkanis Bruice

 

This is a five-step synthesis of 3-ethlypentane:

 

Step 1. Carbon-carbon bonds are formed, going from a three-carbon chain to a five-carbon pentyne.

Step 2. The pentyne is converted to a pentene, using hydrogen and Na and NH3 (liq).

Step 3. Pentene is converted to 3-bromopentane with HBr. Here we lose half of our product because what actually form are two compounds: 3-bromopentane and 2-bromopentane.

Step 4. Substitution occurs, Br- is the leaving group.

Step 5. The triple bond is reduced to a single bond.