Nucleophilic Substitution in Haloalkanes

Study Notes

Occurs when a nucleophile (a species with a lone pair of electrons) replaces a leaving group (a halogen atom) in a haloalkane
Two types of nucleophilic substitution reactions:
- SN1 (unimolecular nucleophilic substitution): a two-step mechanism involving a carbocation intermediate
- SN2 (bimolecular nucleophilic substitution): a one-step mechanism involving a transition state with a pentacoordinate carbon atom
Factors affecting the rate of nucleophilic substitution reactions:
- Steric hindrance: bulkier substituents reduce the rate of reaction
- Nucleophilicity: stronger nucleophiles increase the rate of reaction
- Leaving group ability: better leaving groups increase the rate of reaction

Occurs when an electrophile (a species with a deficiency of electrons) adds to a haloarene (a halogen-substituted aromatic compound)
Forms a carbocation intermediate, which is stabilized by the aromatic ring
Follows Markovnikov's rule: the electrophile adds to the carbon atom with the greatest number of hydrogen atoms

Haloalkanes:
- SN1: formation of a carbocation intermediate, followed by nucleophilic attack
- SN2: backside attack by the nucleophile, resulting in inversion of stereochemistry
Haloarenes:
- Electrophilic addition: formation of a carbocation intermediate, followed by addition of the electrophile

Haloalkanes:
- Higher molecular weight and boiling point compared to corresponding alkanes
- Higher density and solubility in non-polar solvents
- Lower solubility in water
Haloarenes:
- Higher molecular weight and boiling point compared to corresponding arenes
- Higher density and solubility in non-polar solvents
- Lower solubility in water

Haloalkanes and haloarenes are persistent organic pollutants (POPs) that can accumulate in the environment
Can bioaccumulate in aquatic organisms and biomagnify in food chains
Can cause environmental harm through:
- Ozone depletion (chlorofluorocarbons, CFCs)
- Toxicity to aquatic organisms
- Contamination of soil and groundwater
- Potential human health risks through exposure to contaminated food and water

Nucleophilic substitution reaction involves replacement of a leaving group (halogen atom) by a nucleophile (species with a lone pair of electrons) in a haloalkane
Two types of nucleophilic substitution reactions: SN1 (unimolecular) and SN2 (bimolecular)
SN1 involves a two-step mechanism with a carbocation intermediate, while SN2 involves a one-step mechanism with a pentacoordinate carbon atom in the transition state
Factors affecting rate of nucleophilic substitution reactions:
- Steric hindrance: bulkier substituents reduce reaction rate
- Nucleophilicity: stronger nucleophiles increase reaction rate
- Leaving group ability: better leaving groups increase reaction rate

Electrophilic addition reaction involves addition of an electrophile (species with a deficiency of electrons) to a haloarene (halogen-substituted aromatic compound)
Reaction forms a carbocation intermediate, stabilized by the aromatic ring
Follows Markovnikov's rule: electrophile adds to carbon atom with the greatest number of hydrogen atoms

Haloalkanes:
- SN1: formation of carbocation intermediate, followed by nucleophilic attack
- SN2: backside attack by nucleophile, resulting in inversion of stereochemistry
Haloarenes:
- Electrophilic addition: formation of carbocation intermediate, followed by addition of electrophile

Haloalkanes:
- Have higher molecular weight and boiling point compared to corresponding alkanes
- Have higher density and solubility in non-polar solvents
- Have lower solubility in water
Haloarenes:
- Have higher molecular weight and boiling point compared to corresponding arenes
- Have higher density and solubility in non-polar solvents
- Have lower solubility in water

Haloalkanes and haloarenes are persistent organic pollutants (POPs) that accumulate in the environment
Can bioaccumulate in aquatic organisms and biomagnify in food chains
Environmental harm caused by:
- Ozone depletion (chlorofluorocarbons, CFCs)
- Toxicity to aquatic organisms
- Contamination of soil and groundwater
- Potential human health risks through exposure to contaminated food and water