What type of reaction is exhibit by alkenes?

Question

i need it badly..i'm so tired of searching for answers..can anyone help me..and can you tell me the reactions of concentrated sulfuric acid in benzene, n-hexane, cyclohexane, kerosene and gasoline.. and can you please give the explanation..thaks!

Answer 1

It is useful to first identify what is the nucleophile and what is the electrophile. In this case, the nucleophile is the pi system of the substrate (double bond) and the electophile is a proton from sulfuric acid. So the addition of hydrogen to the substrate will first occur, leaving a positive charge on the most substituted carbon. Next a nucleophile must come in. Even though sulfuric acid is concentrated, you will have water floating around. After the attack of the carbocation and a simple deprotonation step, you will be left with an alcohol. My first concern with your question is that cyclohexane and n-hexane are not alkenes. Secondly for this type of addition of -OH to occur, the reaction must go through a tertiary carbocation intermediate. Finally, it is highly unlikely that you are going to disturb the aromatic system of bezene by doing an addition of -OH onto it. If you really wanted to do that, you would have to use very specialized conditions such functionalizing the ring, carrying out a dissolving metal reduction, and follwing up with more steps yet. You can do, however, an electrophilic aromatic substitution to give bezenesulfonic acid as the product.

Answer 2

Alkenes can only react at the double bond, by using the pair of electrons used to form the double bond to bond with something else, usually something with a positive charge. In acidic conditions, like conc. H2SO4, the electrons from the double bond will reach out and grab an H+ ion. The H+ will end up bound to one of the carbons from the double bond. The other will have a + charge, and will generally bond with whatever around it has a - charge, although I've never seen it bond to HSO4- before.