Orgo 8.8-8.10

halogens add to alkenes to form __. 
A halogen molecule is __; a nucleophile can react with a halogen, displacing a __.

In some reactions, the pi electrons of an alkene attack the bromine molecule, doing what? A __ results, containing a 3-membered ring with a positive charge on the bromine atom. This __ is similar to the __. Similar reactions with other halogens form other __. The structures of a __, a __, and an __ also exist.

Unlike a normal carbocation, all the atoms in a halonium ion have __.
The three-membered ring has considerable __, which, combined with a ositive charge on an electronegative halogen atom, makes the __ strongly electrophilic. Attack by a nucleophile does what?

Addition of Halogens to Alkenes

Cl and Br commonly add to alkenes by the __. Iodination is used less frequently because __ products decompose easily. Any solvents used must be __ to the halogens; methylene chloride, chloroform, and carbon tetrachloride are the most frequent choices

The addition of bromine to cyclopentene is a stereospecific __.

__ results from the bromonium ion mechanism. When a nucleophile attacks a __, it must do so from the __, assuring __.

Halogen addition is another example of a __, in which different stereoisomers of the starting material give different stereoisomers of the product

A __ is an alcohol with a halogen on the adjacent carbon atom. In the presence of water, halogens add to alkenes to form __. The electrophilic halogen adds to the alkene to give a __, which is also electrophilic. Water acts as a nucleophile to open the __ and form the __.

Formation of halohydrins

When __takes place with no solvent or with an inert solvent such as CCl4 or CHCl3, only the halide ion is available as a nucleophile to attack the __. A __ results.

But when an alkene reacts with a haogen in the presence of a nucleophilic solvent such as water, a slovent molecule is the most likely nucleophile ot attack the __. When a water molecule attacks the __, the final product is a __, with a halogen on one carbon atom and a __ on the adjacent carbon. The product may be a __, __, or an __, depending on the halogen.

Stereochemistry of Halohydrin Formation

-because the mechanism involves a halonium ion, the __ of addition is __, as in __.

Orientaton of Halohydrin Formation
- even though a __ is invovled, rather than a carbocation, the extended version of __ applies to __. When propene reacts with chlorine water, the major product has the electrophile chlorine atom) bonded to the __ of the double bond. The mucleophile is bonded to the __.

The __ observed in halohydrin formation is explained by the structure of the __. The two carbon atoms bonded to the halogen have__, with a __ on the more subbed carbon atom. The nucleophile attacks this more subbed, more electrophilic carbon atom. The result is both __ and __.

Hydrogenation of an alkene is formally a __, with H2 adding across the double bond to give an __, the process usually requires a catalyst containing Pt, Pd, or Ni.

For most alkenes, __ takes place at room temp, using hydrogen gas at __. The alkene is usually dissolved in an __, an __, or __.

A small amount of __, __, or __ is added, and the container is shaken or stirred while the reaction proceeds. Hydrogenation actually takes palce at the surface of the __, where the liquid solution of the alkene comes into contact with __ and the __.

Hydrogen gas is __ onto the surface of these __, and the catalyst weakens the H-H bond. In fact, if H2 and D2 are mixed in the presence of a platinum catalyst, the two isotopes quickly scramble  to produce a random mixture of HD, H2, and D2. No scarambling occurs in the __.

Hydrogenation is an example of __, because the (solid) catalyst is in a different phase from the reactant solution. In contrast, __ involves reactants and catalyst in the same phase, as in the acid-catalyzed dehydration of an alcohol.

Because the two hydrogen atoms add from a solid surface, they add with __ stereochemistry. 

Soluble homogeneous catalysts, such as __, also catalyze the hydrogenation of C=C

Wilkinson's catalyst is not __, but its __ can be replaced by __ to give __ that are capable of converting optically inactive starting materials to optically active products. Such a process is called __ or __.

__ is particularly important in the pharmaceutical industry because only one enantiomer of a chiral drug is likely to have the desired effect.

The correct enantiomer can be synthesized from an __starting material by __ using a complex of rhodium with a chiral ligand called __. Such an __ is more efficient than making a __, resolving it into __, and discarding the unwanted __.