Question

Short answer

1. No
2. No
3. Yes
4. Yes

Step-by-step solution

Electrophile

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

Nucleophile

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

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

Explanation

a. \({\rm{B}}{{\rm{r}}^{\rm{ - }}}\) 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 \({\rm{O}}{{\rm{H}}^{\rm{ - }}}\) 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. \({\rm{C}}{{\rm{N}}^{\rm{ - }}}\) is a nucleophile. Therefore, it has the maximum electron density. The carbon in the C-Cl bond is an electrophile. Therefore, the \({\rm{C}}{{\rm{N}}^{\rm{ - }}}\) 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 \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\) bond is an electrophile. Therefore, the alkene attacks at the electrophilic position, and hence the reaction occurs.

Representation of electrophile and nucleophile