Question: By using only electron density arguments, determine whether the following reactions will occur.

a.

b.

c.

d.

Electrophiles are electron-deficient and electron-loving species. The bonded atom (less electronegative) with an electronegative atom is always an electron-deficient species.

Nucleophiles are electron-rich and electron-hating species. The one condition to fulfill the criterion of a nucleophile is that a nucleophile must have one lone pair of electrons.

Electron density is the maximum at nucleophiles and the minimum at electrophiles. The reaction occurs only with an electrophile and a nucleophile.

a. $B{r}^{-}$is a nucleophile. Therefore, it has the maximum electron density. The benzene ring is also a nucleophile having the maximum electron density. Therefore, the reaction does not occur.

Representation of reaction

b. The $O{H}^{-}$is a nucleophile. Therefore, it has the maximum electron density. The cycloalkene is also a nucleophile. Therefore, the reaction does not occur.

Representation of reaction

c. $C{N}^{-}$is a nucleophile. Therefore, it has the maximum electron density. The carbon in the C-Cl bond is an electrophile. Therefore, the $C{N}^{-}$ attacks at the electrophilic position, and hence the reaction occurs.

Representation of electrophile and nucleophile

d. Alkene is a nucleophile. Therefore, it has the maximum electron density. The $H_3{O}^{+}$bond is an electrophile. Therefore, the alkene attacks at the electrophilic position, and hence the reaction occurs.

Representation of electrophile and nucleophile