Orgo Reactions Midterm 2

Reaction of an Alkene (C=C) with I2 (or any reactive nonmetal in column 17)

Forms a: Halonium/ Iodinium Ion

I2 is electrophilic because its antibonding orbital is the LUMO, so the alkene donates electrons from the HOMO pi bond into the I2 orbital, and I2 bonds to both carbons creating a 3-membered ring

Dihalogenation

The leftover iodide ion from the reaction of an alkene with I2 attacks the antibonding orbital of the existing C-I bond, leading to an I atom on opposite faces of the molecule

(- In a nucleophilic solvent like methanol, methanol can compete with iodide to attack the iodonium ion.

• In a non-nucleophilic solvent, such as dichloromethane (\(\mathrm{CH_2Cl_2}\)), iodide is the nucleophile that attacks, producing the dihalide.)

Anti Addition

Oxymercuration - Reduction

Reagents: 1: Hg(OAc)2, H2O, 2: NaBH4

Product: A Markovnikov alcohol

First, a mericurinium ion is formed like an iodinium ion, where electrophilic mercury reacts with the alkene portion of the molecule (one of the OAc groups drops off), then water attacks the more-substituted carbon, creating OH2 then Oh by deprotonation

Second, NaBH4, a reducing agent, removes the mercury group and replaces it with a hydrogen

Anti addition

Hydroboration-Oxidation

Reagents: 1. (HydroBoration) BH3 2. (oxidation) H2O2 and NaOH

ANTI MARKOVNIKOV PRODUCT

In step 1: Hydrogen attaches to more substituted carbon (with less Hs), and BH2 attatches to the less substituted carbon 2: the BH2 is changed to an OH

Syn Addition

Hydroetherification

alkene combines w alcohol to form an ether with R O R

Acid-catalyzed: Strong acid adds a proton to carbon carbon, then the oxygen atom with OH2, then one H is removed

Transition Metal-Catalyzed: CH3OH (methanol) plus a transition metal. Metal attatches to less substituted carbon, OCH3 to more subsituted carbon, then the metal is swapped for an H and the catalyst is regenerated.

Follows Markovnikov

Radical Reactions

Initiation: When light is added to a weak halogen, it splits the bond creating two radicals, one attatches to the less subsituted carbon, then an electron from the double bond turns a more substituted carbon into a radical, then one radical of original bond left over

Propogation: If another Br2 comes along, it will split, allowing one radical to attatch the Carbon radical while another is generated

Termination: If the two Br radicals are left, they will join and create Br2, not creating more radicals

Radical Hydrobromination - The Effect of Peroxide

if you have HBr as a reactant, it’s difficult to break its bond to create a Br radical, so peroxide, with a breakable O-O bond is used to generate a radical which generates a Br radical when combines with HBr

The Br radical attatches to the less substituted carbon, leaving a radical on the more substituted carbon, then when interacting with HBr it forms more Br radicals and takes on the H

Stereoisomers vs. enantiomers