whats the mech for this: (E)-2,5-dimethyl-hex-3-ene and bromine
CH3-CH(CH3)-CH=CH-CH(CH3)-CH3 + Br2 ->
CH3-CH(CH3)-CH(Br)-CH(Br)-CH(CH3)-CH3
Note that C-2 and C-5 are chiral centres so you may want to restrict your answer by starting with one set of configurations about the chiral centres.
I can't show the stereochemistry, in any case I suggest that you make a model, add the bromine and transcribe the structure.
The bromine will add across the double bond in the usual fashion. This page shows the addition with an example where the Br2 is added across Z and E isomers.
http://en.wikipedia.org/wiki/Halogen_addition_reaction
To determine the reaction mechanism for the reaction between (E)-2,5-dimethyl-hex-3-ene and bromine, we need to consider the type of reaction and the reactivity of the reactants. In this case, we have an alkene reacting with bromine, which suggests that it is a type of addition reaction called electrophilic addition.
In an electrophilic addition reaction, the pi bond of the alkene acts as a nucleophile, attacking an electrophilic species, in this case, bromine (Br2), which is a halogen. The reaction proceeds in several steps:
1. The bromine molecule (Br2) is polarized, with a partial positive charge on the bromine atom due to its electron-withdrawing nature.
2. The pi bond of the (E)-2,5-dimethyl-hex-3-ene acts as a nucleophile, attacking the bromine molecule. One of the carbon atoms in the double bond donates electron density to the bromine atom.
3. A cyclic bromonium ion is formed, where the bromine atom is bonded to one of the carbon atoms of the original double bond, while the other carbon atom has a positive charge.
4. In the next step, a bromide ion (Br-) acts as a nucleophile, attacking the positively charged carbon atom in the bromonium ion. This results in the formation of a new carbon-bromine bond.
5. The last step involves the release of a proton (H+) from the adjacent carbon, resulting in the formation of the final product.
Overall, the reaction mechanism for the reaction between (E)-2,5-dimethyl-hex-3-ene and bromine proceeds through an electrophilic addition mechanism.