Preparing Alkenes:A Preview of Elimination Reactions In biological pathways dehydrations normally take place on substrates in which-OH is positioned two carbons away from a carbonyl group H 0 H3C ACP H30 ACP H20 H B-Hydroxybutyryl ACP trans-Crotonyl ACP In biological pathways dehydrations normally take place on substrates in which –OH is positioned two carbons away from a carbonyl group Preparing Alkenes: A Preview of Elimination Reactions