Physical Properties of Haloalkanes Due to differences in electronegativity, the C-X bond is polar with a net loss of negative charge around the carbon.
As the size of the halogen increases, the strength of the C-X bond decreases. When the halogen's electron cloud increases and becomes more diffuse, the disparity of size between carbon and halogen orbitals increases, which results in weaker bonds.
Because of their polar bond, haloalkanes have higher boiling points than their alkane counterparts. Since London dispersion forces increase as the halogen is less tightly bound to the carbon, boiling point also increases with greater halogen size. Nuceleophilic Substitution Nucleophiles are substances with an unshared electron pair. The nucleophile attacks the electrophilic carbon and replaces the halide. The displaced halide is called the leaving group. SN2-Bimolecular Nucelophilic Sustitution SN2 reactions are a concerted, one-step reaction. The nucleophilic attack on the carbon results in the simultaneous expulsion of the leaving group. There are two potential avenues of displacement, frontside and backside displacement, which are stereospecific.
Structure and Reactivity
The reactivity and rate of reaction are determined by several factors: Leaving Group Substrate Nucleophile charge basicity solvation polarizability molecular structure SN1-Unimolecular Nucelophilic Sustitution Like in SN2 reactions, the final product of SN1 reactions is the substrate bonded with the nucleophile and unbonded from the leaving group. However, these reactions are not stereospecific and occur in three steps: Dissociation of halide to form a carbocation Nucleophilic attack Deprotonation The reactivity and rate of reaction are determined by several factors: Leaving Group Solvation Nucleophile Carbocation Stability Elimination Elimination occurs when the halide is removed with a hydrogen on a neighboring carbon and a double bond forms. E1-Unimolecular Elimination Like in SN1 reactions, the rate limiting step of E1 reactions is the formation of the carbocation. E1 reactions are typically a side reaction to SN1 reactions. However, E1 reactions are favored in the presence of a strong base. E2-Bimolecular Elimination B2 reactions proceed in one step.