HALOALKANES AND HALOARENES - Formula Sheet

Haloalkanes (Alkyl Halides): Organic compounds containing a halogen atom (fluorine, chlorine, bromine, or iodine) attached to a saturated carbon atom.
Haloarenes (Aryl Halides): Organic compounds where a halogen atom is attached to an aromatic ring (e.g., chlorobenzene).

Monohaloalkanes: Compounds containing only one halogen atom attached to a saturated carbon chain.
Example: Methyl chloride \(CH_3Cl\), Ethyl bromide \(C_2H_5Br\).
Polyhaloalkanes: Compounds containing more than one halogen atom attached to a saturated carbon chain.
Example: Dichloromethane \(CH_2Cl_2\), Trichloroethylene \(C_2HCl_3\).
Aryl Halides: Compounds containing a halogen atom attached to an aromatic ring.
Example: Chlorobenzene \(C_6H_5Cl\), Bromobenzene \(C_6H_5Br\).

Name the alkane chain as per IUPAC rules.
Add the halogen as a substituent with a prefix: Fluoro-, Chloro-, Bromo-, Iodo-.
Number the chain to give the halogen the lowest possible number.
Example: 1-Bromobutane, 2-Chloro-3-methylpentane.

From Alcohols: Alcohols can be converted to haloalkanes by halogenation using reagents like \(PCl_5\), \(SOCl_2\), or HX.
Example: \(C_2H_5OH + HCl \rightarrow C_2H_5Cl + H_2O\).
From Alkenes (Electrophilic Addition): Alkenes can react with halogens (e.g., Br₂, Cl₂) to form haloalkanes.
Example: Ethene reacts with HCl to form ethyl chloride.
From Hydrocarbons (Radical Substitution): Haloalkanes can be prepared by halogenation of alkanes in the presence of UV light.
Example: Methane reacts with chlorine in UV light to form methyl chloride.

Physical Properties:
Haloalkanes are generally colorless, volatile liquids with a distinctive odor.
They are immiscible with water but soluble in organic solvents.
Their boiling points increase with the size of the halogen.
Chemical Properties:
Nucleophilic Substitution: Haloalkanes undergo nucleophilic substitution reactions where the halogen is replaced by a nucleophile (e.g., OH⁻, NH₃).
Example: \(C_2H_5Cl + OH^- \rightarrow C_2H_5OH + Cl^-\).
Elimination Reactions: Haloalkanes can undergo elimination reactions to form alkenes.
Example: 2-Bromoethane undergoes elimination in the presence of KOH to form ethene.
Reduction: Haloalkanes can be reduced to alkanes.
Example: Methyl chloride can be reduced to methane using a reducing agent.

Structure: In haloarenes, the halogen atom is attached to a benzene ring. The halogen atom can either be attached directly to the ring or as part of a polyhalogenated structure.
Example: Chlorobenzene, \(C_6H_5Cl\), and 1,2,4-Trichlorobenzene.

Halogenation of Aromatic Compounds: Aromatic compounds can be halogenated in the presence of a halogen and a catalyst (e.g., ferric chloride \(FeCl_3\)).
Example: Benzene reacts with chlorine in the presence of FeCl₃ to form chlorobenzene.
From Alkyl Halides: Haloalkanes can be converted to haloarenes by nucleophilic substitution using aromatic compounds.
Example: Methyl iodide reacts with benzene in the presence of a strong base to form methylbenzene.

Physical Properties:
Haloarenes are generally colorless liquids with a sweet odor.
They are less reactive and less soluble in water than haloalkanes due to the delocalized π-electrons in the benzene ring.
Chemical Properties:
Electrophilic Substitution: Haloarenes undergo electrophilic substitution reactions, such as nitration, sulfonation, and Friedel-Crafts reactions.
Example: Chlorobenzene reacts with nitrating agents to form nitrobenzene.
Nucleophilic Substitution: Haloarenes undergo nucleophilic substitution under suitable conditions.
Example: Chlorobenzene reacts with sodium hydroxide in the presence of high temperature to form phenol.

Haloalkanes:
Used as solvents, refrigerants, and as intermediates in the synthesis of pharmaceuticals and agrochemicals.
Example: Dichloromethane is used as a solvent in paint removers and degreasing agents.
Haloarenes:
Used in the preparation of agrochemicals, pharmaceuticals, and as solvents in chemical processes.
Example: Chlorobenzene is used as a solvent in the manufacture of pesticides.

Reactivity of Haloalkanes: The reactivity of haloalkanes is mainly governed by the bond strength between the carbon and halogen. The halogen atom can be replaced by a nucleophile in a substitution reaction or removed via elimination.
Reactivity of Haloarenes: Haloarenes tend to undergo substitution reactions rather than addition due to the stability of the aromatic ring. The halogen substituent in haloarenes deactivates the ring towards electrophilic substitution but activates it towards nucleophilic substitution.

SN1 Mechanism:
This occurs in two steps: first, the leaving group departs to form a carbocation intermediate, and then the nucleophile attacks the carbocation.
SN1 reactions typically occur in tertiary haloalkanes and in polar solvents.
Example: Tertiary butyl chloride undergoing substitution with water.
SN2 Mechanism:
This occurs in a single step, where the nucleophile attacks the carbon attached to the halogen simultaneously as the leaving group departs.
SN2 reactions typically occur in primary or secondary haloalkanes and in polar aprotic solvents.
Example: Methyl chloride reacting with hydroxide to form methanol.