Haloalkanes and Haloarenes - From Hydrocarbons through Free Radical Halogenation
- Introduction to Haloalkanes and Haloarenes
- Substitution reactions
- Halogenation of hydrocarbons
- Nomenclature of Haloalkanes
- Examples and equations
Introduction to Haloalkanes and Haloarenes
- Haloalkanes: Organic compounds containing a halogen atom bonded to an alkyl group.
- Haloarenes: Organic compounds containing a halogen atom bonded to an aryl group.
- Important halogens: Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).
- Chloroalkanes and chloroarenes are most frequently studied.
Substitution Reactions
- In a substitution reaction, an atom or group of atoms is replaced by another atom or group of atoms.
- In haloalkanes and haloarenes, halogen atom(s) are replaced by other atoms or groups.
- Examples of substitution reactions:
- SN1: Unimolecular nucleophilic substitution
- SN2: Bimolecular nucleophilic substitution
Halogenation of Hydrocarbons
- Halogenation is a type of substitution reaction.
- Alkanes can undergo free radical halogenation in the presence of a halogen (such as chlorine or bromine) and heat or light.
- Initiation, propagation, and termination are the three key steps in halogenation reactions.
- Example equation: CH₄ + Cl₂ → CH₃Cl + HCl
Nomenclature of Haloalkanes
- Haloalkanes are named using the same rules as alkanes.
- The halogen is considered as a substituent and is indicated by the prefix fluoro-, chloro-, bromo-, or iodo-.
- Numbering of the parent chain is done to give the lowest possible number to the substituent.
- Examples:
- CH₃Cl: Chloromethane
- CH₃CH₂Br: Bromoethane
Examples and Equations: Haloalkanes
- CH₃Cl: Chloromethane
- CH₃Br: Bromomethane
- CH₃CH₂Cl: Chloroethane
- CH₃CH₂Br: Bromoethane
- CH₃CH₂CH₂Cl: 1-Chloropropane
Examples and Equations: Haloarenes
- C₆H₅Cl: Chlorobenzene
- C₆H₅Br: Bromobenzene
- C₆H₄Cl₂: 1,2-Dichlorobenzene
- C₆H₃Cl₃: 1,2,3-Trichlorobenzene
- C₆H₂Cl₃Br: 1,3,5-Trichloro-2-bromobenzene
Haloalkanes and Haloarenes - From Hydrocarbons through Free Radical Halogenation
- Introduction to Haloalkanes and Haloarenes
- Substitution reactions
- Halogenation of hydrocarbons
- Nomenclature of Haloalkanes
- Examples and equations
Introduction to Haloalkanes and Haloarenes
- Haloalkanes: Organic compounds containing a halogen atom bonded to an alkyl group.
- Haloarenes: Organic compounds containing a halogen atom bonded to an aryl group.
- Important halogens: Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).
- Chloroalkanes and chloroarenes are most frequently studied.
Sure! Here are slides 11 to 20 for the topic “Haloalkanes and Haloarenes - From Hydrocarbons through Free Radical Halogenation”:
Slide 11
- Substitution Reactions
- SN1: Unimolecular nucleophilic substitution
- Involves a two-step mechanism
- Nucleophile attacks the carbocation formed
- Racemization may occur if chiral compounds are involved
- Examples: CH₃CH₂Cl → CH₃CH₂OH + Cl⁻
- SN2: Bimolecular nucleophilic substitution
- Involves a one-step concerted mechanism
- Nucleophile attacks the substrate as a leaving group leaves
- Always results in inversion of stereochemistry
- Examples: CH₃CH₂Cl + OH⁻ → CH₃CH₂OH + Cl⁻
Slide 12
- Free Radical Halogenation
- Initiation: Formation of free radicals
- Requires heat or light
- Example: Cl₂ → 2Cl· (free radicals)
- Propagation: Chain reactions
- Formation and consumption of free radicals
- Examples: CH₄ + Cl· → CH₃· + HCl
CH₃· + Cl₂ → CH₃Cl + Cl·
- Termination: Combination of free radicals
- Free radicals combine to form stable compounds
- Examples: 2Cl· → Cl₂
Cl· + CH₄ → CH₃Cl
Slide 13
- Factors Affecting Substitution Reactions
- Nature of substrate or alkyl group
- Increases in the order: Methyl < Primary < Secondary < Tertiary
- Tertiary substrates undergo substitution reactions faster
- Nucleophile strength
- Strong nucleophiles are more reactive
- Examples: OH⁻ > H₂O, NH₂⁻ > NH₃, Br⁻ > Cl⁻
- Polar aprotic solvents favor SN2 reactions
- Leaving group ability
- Good leaving groups are more reactive
- Examples: I⁻ > Br⁻ > Cl⁻ > F⁻
- Leaving group ability affects the rate of SN1 reactions
Slide 14
- Reactions of Haloalkanes: Elimination
- Elimination reactions involve the removal of atoms or groups to form multiple bonds.
- Examples: Dehydrohalogenation and Dehydration
- Types:
- E1: Unimolecular elimination reactions
- Involves formation of carbocation and subsequent loss of a proton
- Examples: CH₃CH₂Cl → CH₂=CH₂ + HCl
- E2: Bimolecular elimination reactions
- Involves a one-step concerted mechanism
- Alkyl halide and base react to form an alkene
Slide 15
- Reactions of Haloalkanes: Reaction with Metals
- Reaction of alkyl halides with highly reactive metals
- Reduction and coupling reactions
- Examples:
- RX + 2Na → RNa + NaX
- 2RX + Zn → R-R + ZnX₂
Slide 16
- Reactions of Haloalkanes: Reaction with Amines
- Reaction of alkyl halides with amines
- Substitution or elimination reactions depending on conditions
- Examples:
- RX + NH₃ → RNH₂ + HX
- RX + NH₂R’ → RNHR’ + HX
Slide 17
- Nomenclature of Haloarenes
- Haloarenes are named using the same rules as arenes (benzene derivatives).
- The halogen is considered as a substituent and is indicated by the prefix fluoro-, chloro-, bromo-, or iodo-.
- Numbering of the carbon atoms in the benzene ring is done to give the lowest possible number to the substituent.
- Examples: ClC₆H₄CH₃: 4-Chlorotoluene
BrC₆H₄CH₂CH₃: 2-Bromoethylbenzene
Slide 18
- Examples and Equations: Haloalkanes
- 1-Chlorobutane: CH₃CH₂CH₂CH₂Cl
- 2-Bromopropane: CH₃CHBrCH₃
- 2-Chloro-3-fluorobutane: CH₃CHClCH₂CH₂CF₃
Slide 19
- Examples and Equations: Haloarenes
- 1-Bromobenzene: C₆H₅Br
- 1-Chloro-4-nitrobenzene: ClC₆H₄NO₂
- 1,3-Dichlorobenzene: ClC₆H₄Cl
Slide 20
- Summary
- Haloalkanes and haloarenes are organic compounds containing halogen atoms bonded to alkyl or aryl groups.
- Substitution reactions involve replacing halogen atoms with other atoms or groups.
- Free radical halogenation is a common type of substitution reaction in hydrocarbons.
- Nomenclature and naming of haloalkanes and haloarenes follow specific rules.
- Examples and equations provide a better understanding of these compounds and reactions.
Sure! Here are slides 21 to 30 on the topic “Haloalkanes and Haloarenes - From Hydrocarbons through Free Radical Halogenation”:
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Reactions of Haloarenes: Nucleophilic Aromatic Substitution (SNAr)
- Haloarenes undergo nucleophilic substitution reactions
- Electrophilic attack on the aromatic ring
- The attack occurs at the position ortho or para to the halogen
- Examples:
- C₆H₅Cl + NaOH → C₆H₅OH + NaCl
- C₆H₅Br + NH₃ → C₆H₅NH₂ + HBr
Reactions of Haloarenes: Electrophilic Aromatic Substitution
- Haloarenes can undergo electrophilic aromatic substitution (EAS)
- Electrophile substitutes an atom or group in the aromatic ring
- Examples:
- C₆H₅Cl + AlCl₃ → C₆H₄Cl₂ + HCl
- C₆H₅Br + HNO₃ → C₆H₄BrNO₂ + HBr
Reactions of Haloarenes: Sandmeyer Reaction
- Sandmeyer reaction is used to convert aryl halides into various functional groups
- Substitution of the halide by other groups (such as -CN, -OH, -F, -Br, -I)
- Example:
- C₆H₅Cl + CuCN → C₆H₅CN + CuCl
Stereochemistry of Haloalkanes
- Haloalkanes can exhibit stereoisomerism
- Chiral carbon atoms can lead to enantiomers and optical isomers
- Examples:
- 2-Chlorobutane has two enantiomers
- 1-Bromo-1-chloropropane has no optical isomers
Environmental Impact of Haloalkanes and Haloarenes
- Haloalkanes and haloarenes have harmful effects on the environment
- Persistence, bioaccumulation, and toxicity (PBT) properties
- Examples:
- CFCs (Chlorofluorocarbons) deplete ozone layer
- PCBs (Polychlorinated biphenyls) are persistent organic pollutants
Uses of Haloalkanes and Haloarenes
- Haloalkanes and haloarenes have various applications
- Solvents, refrigerants, pharmaceuticals, pesticides, etc.
- Examples:
- Tetrachloroethylene is used in dry cleaning
- Chlorobenzene is used in synthesis of chemicals
Industrial Importance of Haloalkanes and Haloarenes
- Haloalkanes and haloarenes are important in industrial processes
- Synthesis of various compounds and intermediates
- Examples:
- Chloroform is used as a solvent and reagent in laboratory and industry
- Tetrachloromethane is used in fire extinguishers
Safety Precautions with Haloalkanes and Haloarenes
- Haloalkanes and haloarenes can be hazardous
- Proper handling and disposal is necessary
- Examples:
- Use in well-ventilated areas
- Wear protective clothing and gloves
Summary
- Haloalkanes and haloarenes undergo substitution reactions and halogenation of hydrocarbons.
- Nucleophilic and electrophilic substitution reactions are common.
- Haloarenes can undergo SNAr and EAS reactions.
- Sterechemistry, environmental impact, and applications should be considered.
- Safety precautions should be taken when handling these compounds.
Questions to Test Your Understanding
- What are the different types of substitution reactions for haloalkanes? Provide examples.
- Describe the steps involved in free radical halogenation of hydrocarbons.
- How do you name haloalkanes and haloarenes? Give examples.
- What are the factors that affect substitution reactions?
- Explain the Sandmeyer reaction and its applications.
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