Draw the structures of organic compounds A and B. Indicate stereochemistry where applicable. The starting material is ethyne, a carbon carbon triple bond where each carbon is bonded to a hydrogen. Step 1 reacts with n butyl lithium followed by 1 equivalent of ethyl bromide to form compound A. Compound A reacts with 1 equivalent of B r 2 in C H 2 C H 2 to form compound B. Compound B reacts with H 2 with palladium on carbon to give a four carbon chain with a bromine substituent on carbons 1 and 2.