Haloalkanes and Haloarenes - Nature of C-X bond

• Introduction
  • Haloalkanes and haloarenes are organic compounds that contain halogens (F, Cl, Br, I) bonded to carbon atoms.
  • The nature of the carbon-halogen bond (C-X bond) plays a crucial role in determining the physical and chemical properties of these compounds.

Definition

• The C-X bond can be defined as the bond formed between a carbon atom and a halogen atom (F, Cl, Br, I) in haloalkanes and haloarenes.

Characteristics of C-X bond

• Covalent character: C-X bond is mostly covalent in nature.
• Polar nature: The C-X bond is polar due to the difference in electronegativity between carbon (2.5) and halogen atoms (F - 3.98, Cl - 3.16, Br - 2.96, I - 2.66).
• Bond strength: The strength of the C-X bond depends on the size and electronegativity of the halogen atom.

Polar nature of C-X bond

• The C-X bond is polar because the halogen atom’s electronegativity is higher than that of carbon.
• As a result, the halogen atom attracts the shared electrons more towards itself, creating a partial positive charge on the carbon atom and a partial negative charge on the halogen atom.
• This polarity gives rise to several important properties of haloalkanes and haloarenes, such as their reactivity and solubility.

Factors affecting the polarity of C-X bond

• Electronegativity difference: The larger the electronegativity difference between the carbon and halogen atom, the more polar the C-X bond.
• Bond length: As the size of the halogen atom increases, the bond length increases, decreasing the polarity of the C-X bond.
• Inductive effect: Electron-withdrawing groups attached to the carbon atom can increase the polarity of the C-X bond by pulling the electron density away from carbon.

Examples

• Chloroethane (CH3CH2Cl)
• Bromobenzene (C6H5Br)
• Iodoform (CHI3)

Equations

• Formation of a C-Cl bond in chloroethane: CH3CH2 + Cl2 → CH3CH2Cl + HCl
• Formation of a C-Br bond in bromobenzene: C6H6 + Br2 → C6H5Br + HBr
• Formation of a C-I bond in iodoform: CHI3 + 2NaOH → CNa3 + NaI + H2O Sure, here are slides 11 to 20 on the topic “Haloalkanes and Haloarenes - Nature of C-X bond”:

11. Functional Group Identification

• Haloalkanes contain the functional group -RX, where R represents an alkyl group (e.g., CH3, C2H5) and X represents a halogen atom.
• Haloarenes contain the functional group -ArX, where Ar represents an aryl group (e.g., phenyl) and X represents a halogen atom.
• These functional groups are responsible for the chemical properties of haloalkanes and haloarenes.

12. Reactivity of C-X bond

• The reactivity of the C-X bond in haloalkanes and haloarenes varies depending on the type of halogen atom.
• Generally, the reactivity increases in the order: I < Br < Cl < F.
• This trend is due to the decrease in bond strength and increase in bond polarity as the size of the halogen atom decreases.

13. Nucleophilic Substitution Reactions

• Haloalkanes and haloarenes undergo nucleophilic substitution reactions, where a nucleophile replaces the halogen atom bonded to carbon.
• In these reactions, the polarity of the C-X bond makes the carbon atom electrophilic (electron-loving) and susceptible to nucleophilic attack.
• The rate of substitution reactions follows the order: R - F > R - Cl > R - Br > R - I (R represents an alkyl or aryl group).

14. Elimination Reactions

• Haloalkanes with strong bases can undergo elimination reactions, where a halogen atom is eliminated along with a hydrogen atom to form an alkene or an alkyne.
• These reactions are more favorable for secondary and tertiary haloalkanes as they have weaker C-X bonds compared to primary haloalkanes.
• The rate of elimination reactions follows the order: R - I > R - Br > R - Cl > R - F (R represents an alkyl group).

15. Solubility of Haloalkanes and Haloarenes

• The solubility of haloalkanes and haloarenes decreases with increasing carbon chain length due to their non-polarity.
• However, haloalkanes and haloarenes are soluble in non-polar solvents such as chloroform and carbon tetrachloride.
• The presence of polar functional groups (e.g., hydroxyl group) increases the solubility of haloalkanes and haloarenes in water.

16. Environmental Impact

• Haloalkanes and haloarenes have adverse effects on the environment due to their persistence and toxicity.
• They can be a source of air, water, and soil pollution if not properly disposed of or used in controlled quantities.
• Regulations have been implemented to control and limit the use of certain haloalkanes and haloarenes due to their environmental impact.

17. Industrial Applications

• Haloalkanes and haloarenes have several industrial applications.
• Some haloalkanes are used as refrigerants (e.g., chlorofluorocarbons - CFCs), solvents, and flame retardants.
• Haloarenes find applications as starting materials in the synthesis of pharmaceuticals, dyes, and agrochemicals.

18. Naming Haloalkanes

• Haloalkanes are named using the IUPAC nomenclature system.
• The halogen atom is considered as a substituent and is named with the prefix fluoro-, chloro-, bromo-, or iodo-.
• The parent chain is named based on the longest carbon chain containing the halogen atom.

19. Naming Haloarenes

• Haloarenes are also named using the IUPAC nomenclature system.
• The halogen atom is considered as a substituent and is named with the prefix fluoro-, chloro-, bromo-, or iodo-.
• The parent compound is named based on the aromatic ring to which the halogen atom is attached.

20. Summary

• The C-X bond in haloalkanes and haloarenes is polar due to the difference in electronegativity between carbon and halogen atoms.
• The polarity of the C-X bond affects the physical and chemical properties of these compounds.
• Haloalkanes and haloarenes undergo nucleophilic substitution and elimination reactions.
• They have specific solubility characteristics and can have adverse environmental effects.
• Proper nomenclature is used for naming haloalkanes and haloarenes based on the IUPAC system. ' Sure, here are slides 21 to 30 on the topic “Haloalkanes and Haloarenes - Nature of C-X bond”:

21. Chemical Reactions of Haloalkanes

• Haloalkanes undergo various chemical reactions such as nucleophilic substitution, elimination, and oxidation reactions.
• Nucleophilic substitution reactions involve the replacement of a halogen atom by a nucleophile.
• Elimination reactions result in the removal of a halogen atom along with a hydrogen atom to form an alkene or alkyne.
• Oxidation reactions convert primary and secondary haloalkanes into alcohols.

22. Nucleophilic Substitution Reactions of Haloalkanes

• Nucleophilic substitution reactions occur through either the SN1 or SN2 mechanism.
• In an SN1 reaction, the halogen atom leaves first, forming a carbocation, which is then attacked by a nucleophile.
• In an SN2 reaction, the nucleophile attacks the carbon atom bearing the halogen atom while the halogen atom leaves.

23. Examples of Nucleophilic Substitution Reactions

• SN1 reaction example:
  • CH3Cl + H2O → CH3OH + HCl
• SN2 reaction example:
  • CH3Cl + NH3 → CH3NH2 + HCl

24. Elimination Reactions of Haloalkanes

• Elimination reactions can occur either via an E1 or E2 mechanism.
• In an E1 reaction, the halogen atom leaves first, forming a carbocation, followed by the removal of a hydrogen atom to form a double bond.
• In an E2 reaction, the halogen atom leaves while a base abstracts a hydrogen atom from an adjacent carbon, forming a double bond.

25. Examples of Elimination Reactions

• E1 reaction example:
  • (CH3)3CCl → (CH3)2C=CH2 + HCl
• E2 reaction example:
  • CH3CH2Cl + KOH → CH2=CH2 + KCl + H2O

26. Oxidation of Haloalkanes

• Primary and secondary haloalkanes can be oxidized to alcohols using oxidizing agents such as potassium permanganate (KMnO4) or acidified potassium dichromate (K2Cr2O7).
• Tertiary haloalkanes do not undergo oxidation reactions.

27. Chemical Reactions of Haloarenes

• Haloarenes undergo various chemical reactions similar to haloalkanes.
• However, their reactivity is relatively lower due to the resonance stabilization provided by the aromatic ring.

28. Examples of Reactions of Haloarenes

• Nucleophilic substitution:
  • C6H5Cl + NaOH → C6H5OH + NaCl
• Elimination:
  • C6H5Br + KOH → C6H5-C≡CH + KBr + H2O
• Oxidation:
  • C6H5Cl + KMnO4 → C6H4O2 + KCl + MnO2

29. Significance of Haloalkanes and Haloarenes

• Haloalkanes and haloarenes are widely used as intermediates in the synthesis of various organic compounds.
• They find applications in pharmaceuticals, pesticides, plastics, refrigerants, and other industrial products.
• Understanding their reactivity and properties is essential for designing and developing new molecules for industrial and medicinal purposes.

30. Summary and Key Points

• Haloalkanes and haloarenes contain a carbon-halogen bond (C-X) that is polar due to the electronegativity difference between carbon and halogen atoms.
• The polarity of the C-X bond affects their physical properties, reactivity, and solubility.
• Chemical reactions of haloalkanes include nucleophilic substitution, elimination, and oxidation reactions.
• Haloarenes have similar reactions but their reactivity is lower due to resonance stabilization.
• Proper nomenclature is essential for naming haloalkanes and haloarenes.
• Understanding the significance and applications of haloalkanes and haloarenes is crucial in the field of organic chemistry.