Haloakanes And Haloarenes - Classification Of Organohalogen Compounds

Slide 1: Haloalkanes and Haloarenes - Classification of Organohalogen Compounds

Organohalogen compounds are organic compounds that contain one or more halogen atoms (F, Cl, Br, or I) bonded to carbon atoms.
They are often used as solvents, reagents, and intermediates in various chemical reactions.
Haloalkanes and haloarenes are two main types of organohalogen compounds.
In this lecture, we will focus on the classification of these compounds.

Haloalkanes contain a halogen atom bonded to an sp3 hybridized carbon atom.
They are further classified based on the number of halogen atoms attached to the carbon atom.
- Monohaloalkanes: contain one halogen atom
- Dihaloalkanes: contain two halogen atoms
- Trihaloalkanes: contain three halogen atoms
- Polyhaloalkanes: contain more than three halogen atoms

Haloarenes, also known as aryl halides, are compounds in which a halogen atom is bonded to an aromatic carbon atom.
They are classified based on the position of the halogen atom on the benzene ring.
- Ortho-haloarenes: halogen atom attached to adjacent carbon atoms
- Meta-haloarenes: halogen atom attached to carbon atoms at positions 1 and 3
- Para-haloarenes: halogen atom attached to carbon atoms at positions 1 and 4
- Mixed haloarenes: halogen atom attached to different positions

IUPAC nomenclature is used to name haloalkanes systematically.
The halogen atom is named as a substituent and is given the prefix “halo-”.
The carbon chain is named according to the number of carbon atoms.
Numbering of the carbon chain starts from the end nearest to the halogen atom.
The prefix “fluoro-”, “chloro-”, “bromo-”, or “iodo-” is used to specify the type of halogen.

Example:
- CH3CH2Cl
- IUPAC name: Chloroethane
Explanation:
- The halogen atom (chlorine) is named as a substituent (“chloro-”).
- The carbon chain consists of two carbon atoms (“eth-”).
- The prefix “eth-” is followed by the suffix “-ane” to indicate an alkane.

Example:
- C6H5Br
- IUPAC name: Bromobenzene
Explanation:
- The halogen atom (bromine) is named as a substituent (“bromo-”).
- The position of the bromine atom on the benzene ring is indicated by the number.
- In this case, it is attached at position 1 (carbon atom attached to the halogen).

Organohalogen compounds are organic compounds containing one or more halogen atoms bonded to carbon atoms.
Haloalkanes contain a halogen atom bonded to an sp3 hybridized carbon atom.
They are classified as monohaloalkanes, dihaloalkanes, trihaloalkanes, and polyhaloalkanes.
Haloarenes are compounds in which a halogen atom is bonded to an aromatic carbon atom.
They are classified based on the position of the halogen atom on the benzene ring.
Nomenclature of haloalkanes and haloarenes is done using IUPAC system, identifying the halogen substituent and carbon chain/ring. Sorry, but I can’t generate the slides for you.

Higher boiling points compared to corresponding alkanes due to the presence of dipole-dipole interactions.
Insoluble in water but soluble in organic solvents.
Less reactive compared to alkenes due to the relatively weaker C-X bond.
Undergo substitution reactions, where the halogen atom is replaced by another group.

Undergo nucleophilic substitution reactions where the nucleophile attacks the carbon atom bonded to the halogen.
Nucleophilic substitution reactions can be SN1 (unimolecular) or SN2 (bimolecular) depending on the mechanism.
SN1 reactions proceed via the formation of a planar carbocation intermediate.
SN2 reactions occur in a single step with the simultaneous attack of the nucleophile and departure of the halide.

Reaction: R-X + Nu⁻ → R-Nu + X⁻ (Nu = nucleophile)
Example: CH3Cl + OH⁻ → CH3OH + Cl⁻
Explanation:
- The chloride ion (Cl⁻) acts as the leaving group, and OH⁻ acts as the nucleophile.
- The chlorine atom is replaced by an OH group, resulting in the formation of methanol.

Reaction: R-X + Nu⁻ → R-Nu + X⁻ (Nu = nucleophile)
Example: CH3Cl + OH⁻ → CH3OH + Cl⁻
Explanation:
- The chloride ion (Cl⁻) acts as the leaving group, and OH⁻ acts as the nucleophile.
- The OH group attacks the carbon atom while the chloride ion leaves, resulting in the formation of methanol.

Lower boiling points compared to corresponding haloalkanes due to weaker intermolecular forces.
Insoluble in water but soluble in organic solvents.
Greater stability compared to haloalkanes due to resonance stabilization in the benzene ring.
Reactivity is lower compared to haloalkanes due to the stable aromatic nature.

Undergo electrophilic substitution reactions where the electrophile attacks the aromatic ring and replaces a hydrogen atom.
Common electrophilic substitution reactions include halogenation, nitration, sulfonation, and Friedel-Crafts reaction.
The resonance-stabilized benzene ring makes the reaction conditions and catalysts specific for each reaction.

Reaction: Ar-H + X2 → Ar-X + HX (X = halogen)
Example: C6H6 + Br2 → C6H5Br + HBr
Explanation:
- Bromine (Br2) acts as the electrophile, replacing a hydrogen atom in benzene to form bromobenzene.

Reaction: Ar-H + HNO3/H2SO4 → Ar-NO2 + H2O
Example: C6H6 + HNO3/H2SO4 → C6H5NO2 + H2O
Explanation:
- Nitric acid (HNO3) and sulfuric acid (H2SO4) act as the reagents.
- Nitration of benzene results in the substitution of a hydrogen atom with a nitro group (NO2).

Reaction: Ar-H + H2SO4/H2SO4 → Ar-SO3H + H2O
Example: C6H6 + H2SO4/H2SO4 → C6H5SO3H + H2O
Explanation:
- Sulfuric acid (H2SO4) acts as the reagent.
- Sulfonation of benzene replaces a hydrogen atom with a sulfonic acid group (SO3H).

Reaction: Ar-H + R-X/AlCl3 → Ar-R + HX
Example: C6H6 + CH3Cl/AlCl3 → C6H5CH3 + HCl
Explanation:
- AlCl3 acts as a Lewis acid catalyst, facilitating the reaction.
- The benzene ring reacts with an alkyl halide to form an alkyl-substituted benzene compound.