HBr example from lecture

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HBr example from lecture

Postby Courtney_Koenig_3K » Thu Mar 02, 2017 1:04 pm

In lecture Dr. Lavelle talks about an example where a HBr molecule is broken and attached to a hydrocarbon. In the example he always attaches the H+ ion first to the hydrocarbon and then the Br- to the hydrocarbon. Does the order that the ions are attached matter? And if it does, then why is the H+ added before the Br-?

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Re: HBr example from lecture

Postby Jenny_Luu_2A » Thu Mar 02, 2017 2:17 pm

In this electrophilic addition example, I think the order does matter, because there are two transition states that need to be drawn for the two steps of the reaction. The nucleophile is first the hydrocarbon, so a pair of electrons goes toward the partially positive hydrogen in the electrophile HBr. Then the hydrogen will break off from the bromine and attach itself to the now electron deficient hydrocarbon. The bromine ion is the new nucleophile and will attach itself to a carbon atom in the hydrocarbon.

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Re: HBr example from lecture

Postby Chem_Mod » Thu Mar 02, 2017 2:25 pm

It definitely matters.

Not possible for pi electrons (NU) to interact (form a bond) with Br- (also a nucleophile).

I have to always give the sequence in class as: pi electrons (NU) interact (form a bond) with electrophile

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