To investigate the effect of the halogen atom on the rate of hydrolysis.

Authors Avatar

Background knowledge

The halogenoalkanes are a vital homologous series, this is due to their importance in organic synthesis, since the halide ion, X-(aq) is an excellent leaving group and may be readily substituted. Halogenoalkanes exist as simple molecules. Between these molecules, van der waals forces as well as dipole- dipole attractions (resulting from the polar C-X bond) operate. The existence of the dipole-dipole attractions explains why halogenoalkanes have slightly higher melting and boiling points when compared with the corresponding alkane.

The general formula for halogenoalkanes is:




              * Where X= fluorine, chlorine, bromine or iodine.

Types of halogenoalkanes

  • Primary (1º)          a halogen is present at the end of the chain:

  • Secondary(2º)            a halogen is present in the body of the chain:

  • Tertiary(3º)             a halogen is present at a branch in of chain:

Strength of bonds

I have included a table of the carbon – halogen bond energies, in which you can see trends between them. The main trend that you see is that the bond energies decrease from Fluorine to Iodine. With that in mind one can predict that due to the shared electrons being closer to the nucleus in fluorine than iodine, iodo-compounds will have the weakest bonds and greatest reactivity while fluorine compounds will have the strongest bonds and least reactivity.

Join now!

Bond Polarity

Halogens are electronegative atoms. Attaching a halogen atom to a carbon atom creates a polar covalent bond. Carbon and halogens have different electronegativities (shown in table below) and halogenoalkanes have polar molecules with a polar C-X bond.

The polarity produces an electron deficient carbon atom, C δ+ which is important in the reactions of halogenoalkanes as it promotes nucleophilic attack, resulting in the displacement of the halide ion. The polarity decreases from fluorine to iodine reflecting the decrease in electronegativity down the halogen group.


This is a preview of the whole essay