• The halogenoalkanes have different?rates?of?substitution?reactions
• Since substitution reactions involve?breaking?the?carbon-halogen?bond the?bond?energies?can be used to explain their different reactivities

Halogenoalkane Bond Energy Table

• The table above shows that the C-I bond requires the least energy to break, and is therefore the?weakest?carbon-halogen bond
• During substitution reactions the C-I bond will therefore?heterolytically?break as follows:

R3C-I + OH-? ? ?→? ? R3C-OH + I-

halogenoalkane? ? ? ? ? alcohol

• The C-F bond, on the other hand, requires the most energy to break and is, therefore, the?strongest?carbon-halogen bond
• Fluoroalkanes will therefore be less likely to undergo substitution reactions

Aqueous silver nitrate

• Reacting halogenoalkanes with?aqueous silver nitrate solution?will result in the formation of a?precipitate
• The?rate of formation?of these precipitates can also be used to determine the reactivity of the halogenoalkanes

Halogenoalkane Precipitates Table

• The formation of the pale yellow silver iodide is the fastest (fastest?nucleophilic substitution?reaction) whereas the formation of the silver fluoride is the slowest (slowest?nucleophilic substitution?reaction)
• This confirms that fluoroalkanes are the least reactive and iodoalkanes are the most reactive halogenoalkanes

The trend in reactivity of halogenoalkanes