Reactivity: How and Why - Organic Chemistry Concepts: An EFL Approach - page 77

B You should have drawn something like.
This shows the electron pair of the hydroxide anion making a heterogenic bond with
the electrophilic carbon which is caused by inductive polarization. At the same time,
the heterolytic loss of bromide occurs.
The reaction is a substitution because only a simple exchange of one single bond for
another occurs. There is no change in bond order or hybridization state at the atomic
centers.
What happens when the non-ionic nucleophile below reacts with an electrophile
such as a proton?
C For this polar reaction to occur, a pair of electrons from the C ] C nucleophile is
shared with the electrophile.
The relatively weakly held π -bond electron pair is used to make the new C-H bond.
The double bond is lost and the remaining carbon, which is one electron short, is a
carbocation. This high energy reactive intermediate needs a nucleophile to finish the
overall reaction.
Can you suggest a suitable nucleophile?
D One example could be a bromide ion. Then the overall reaction becomes:
This reaction has two steps and results in a decrease in the original bond from double
to single. Tetravalent carbon requires that two new single bonds, one on each carbon,
are formed.
This is, of course, the description of an addition reaction. For this change in bond
order to occur, the hybridization state of the carbon centers must change. In this case
it is from sp 2 to sp 3 .
What is the polar reaction if the product alkyl halide is treated with hydroxide?