consider the synthetic sequence shown. identify the reagents for all three steps. draw the structures of organic compounds a and b. omit byproducts. the starting material is a benzene with a c h 2 b r substituent. this reacts with reagent 1 to form compound a. compound a reacts with reagent 2 to form compound b. compound b reacts with reagent 3 to form the product. the product is a 3 carbon chain where carbon 1 is an aldehyde and carbon 3 has a benzene substituent. identify reagent 1. draw compound a.