Haloalkanes: Nomenclature
Haloalkanes are compounds formed by a halogen attached to a carbon chain. They are named by treating the halogen as a substituent of the alkane (e.g., Chloromethane, Chloroethane, 1-Chloropropane).
Physical Properties of Haloalkanes
The physical properties of haloalkanes are related to the significant electronegativity of the halogen, which causes polarization of the C-X bond. They have higher melting and boiling points than alkanes due to dipole interactions. The strength of the C-X bond decreases from fluorine to iodine due to the increase in the size of the halogen orbitals, which overlap less effectively with the sp3 hybrid of carbon.
Bimolecular Nucleophilic Substitution (SN2)
SN2 reactions involve the attack of a nucleophile with lone pairs on a positively polarized carbon, resulting in the loss of the leaving group. The reaction rate depends on the substrate structure, nucleophile nature, leaving group, and solvent.
Unimolecular Nucleophilic Substitution (SN1)
In SN1 reactions, the substrate ionizes to form a carbocation, which is then attacked by the nucleophile in the next step. This reaction only occurs with secondary or tertiary substrates and requires a good leaving group, but the reaction rate does not depend on the nucleophile.
Bimolecular Elimination (E2)
In bimolecular elimination, the base removes hydrogens from the carbon adjacent to the one with the leaving group, forming alkenes. Strong bases, good leaving groups, and an anti-periplanar arrangement of hydrogen to the leaving group are required.
Unimolecular Elimination (E1)
E1 reactions proceed similarly to SN1 by forming a carbocation. Weak bases are required, and carbocation rearrangements can occur.
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