Substitution Reactions

Alkyl halides

Also called electrophiles (Lewis acid), undergo substitution with nucleophiles (Lewis base)

Negatively charged nucleophiles

Like -OH and -SH are used as salts with cations like Li+, etc.

• The identity of the cation is usually inconsequential thus often omitted from the chemical equation

• ________ are usually more reactive than neutral ones because they want to donate electrons; more electrons = more attracted to the nucleus

Cation

Balances the charge in substitution reactions

Formal charge

Number of valence electrons - number of nonbonding VE - (1/2)the number of bonds

Neutral nucleophile

When a ____ is used, the substitution product bears a positive charge

• If the final product has a removable proton, then it will be removed by a B-L base

Nucleophilic substitution product

1. Find the sp3 carbon with the leaving group (look for a polar bond with a partial positive carbon)

2. Identify the nucleophile by looking for a species with a lone pair or $\pi$ bond (negative charge is a huge sign!)

3. Substitute the nucleophiles for the leaving group and assign formal charges to any atom that is involved in bond making and bond breaking

Heterolytically

In a nucleophilic substitution reaction of RX (an alkyl halide), the C-X bond is ________ cleaved and the LG departs with the electron pair in that bond, forming X:^-

more stable

The __________ the leaving group X:^-, the better able it is to accept an electron pair

Weaker

When comparing two LGs, the better leaving group is the _______ base (higher pkb)