This structure  has at its centre surprisingly the feast of unleavened bread. This section itself is a chiasm. The point of the structure we think is to draw attention to the need to leave Egypt behind spiritually as well as physically. 

A. Exodus 11:1-3  Pharaoh gives in and the spoiling of the Egyptians

B. Exodus 11:4-8 The death of the firstborn

C. Exodus 11:9-10 The work is done

D. Exodus 12:1-14 The passover lamb

E. Exodus 12:15-20 Unleavened bread

D’. Exodus 12:21-27 The passover lamb

C. Exodus 12:28 The work is done

B. Exodus 12:29-30 The death of the firstborn

A. Exodus 12:31-36 Pharaoh gives in and the spoiling of the      Egyptians.