Chemistry: ch 6 haloalkanes and haloarenes

icse chem ch 6

Describe the SN1 reaction mechanism

The SN1 reaction mechanism involves two steps:

1. Formation of a carbocation intermediate.

2. Nucleophilic attack on the carbocation to form the final product.

Describe the SN2 reaction mechanism.

The SN2 reaction mechanism is a single-step process where the nucleophile attacks the electrophilic carbon, leading to the simultaneous displacement of the leaving group.

What are the physical properties of Haloalkanes?

Haloalkanes are generally colorless, have higher boiling points than corresponding alkanes, and are often insoluble in water but soluble in organic solvents.

What are the physical properties of Haloarenes?

Haloarenes are typically colorless, have higher boiling and melting points compared to their parent hydrocarbons, and are less reactive than haloalkanes.

What is the difference between SN1 and SN2 reactions?

SN1 reactions are unimolecular nucleophilic substitution reactions involving a two-step mechanism, whereas SN2 reactions are bimolecular nucleophilic substitution reactions involving a single-step mechanism.

How do you distinguish between primary, secondary, and tertiary Haloalkanes?

• Primary Haloalkanes have the halogen atom attached to a carbon atom bonded to only one other carbon.

• Secondary Haloalkanes have the halogen atom attached to a carbon atom bonded to two other carbons.

• Tertiary Haloalkanes have the halogen atom attached to a carbon atom bonded to three other carbons.

What are primary, secondary, and tertiary haloalkanes?

Primary haloalkanes have the halogen atom attached to a carbon atom connected to one other carbon, secondary to two carbons, and tertiary to three carbons.

What is the IUPAC name for CH3CH2Br?

Bromoethane

What factors affect the rate of SN1 reactions

The stability of the carbocation intermediate, solvent polarity, and leaving group ability.

What factors affect the rate of SN2 reactions?

Steric hindrance, nucleophile strength, and leaving group ability.

What is the difference between nucleophilicity and basicity?

Nucleophilicity refers to the ability to donate an electron pair to an electrophile, while basicity refers to the ability to accept a proton.

What is a leaving group?

A leaving group is an atom or group that can depart with an electron pair, forming a stable species.

How are haloarenes prepared

Haloarenes can be prepared by halogenation of aromatic compounds, Sandmeyer reaction, or from diazonium salts.

What is the Sandmeyer reaction

The Sandmeyer reaction involves the conversion of diazonium salts to aryl halides using copper salts.

Why are haloarenes less reactive than haloalkanes?

Due to the resonance stabilization of the aromatic ring and the partial double bond character of the C-X bond.

What are the physical properties of haloalkanes?

Haloalkanes are typically colorless liquids or solids with higher boiling points than alkanes of similar molecular weight.

dehydrohalogenation

Dehydrohalogenation is the elimination of hydrogen halide from haloalkanes, forming alkenes.

What is the role of acetone in SN2 reactions?

: Acetone is a polar aprotic solvent that stabilizes the nucleophile and enhances the rate of SN2 reactions.

: Acetone is a polar aprotic solvent that stabilizes the nucleophile and enhances the rate of SN2 reactions.

• The boiling point increases with the size and mass of the halogen atom due to stronger van der Waals forces.

What is nucleophilic substitution?

Nucleophilic substitution is a reaction where a nucleophile replaces a leaving group in a molecule.

How can haloalkanes be converted to alcohols?

• By reacting them with aqueous KOH or NaOH.

How does the presence of a halogen affect the reactivity of an aromatic ring?

The halogen deactivates the ring and directs electrophilic substitution to the ortho and para positions.

What is the Wurtz reaction?

• The Wurtz reaction involves the coupling of two haloalkanes in the presence of sodium metal to form alkanes.

What are the common methods to synthesize haloalkanes?

Free radical halogenation, electrophilic addition of HX to alkenes, and from alcohols via halogenation.

What is allylic halogenation

• Allylic halogenation involves the substitution of a hydrogen atom at the allylic position with a halogen.

How do haloalkanes undergo elimination reactions?

By losing a hydrogen halide to form alkenes.

What is the stereochemistry of SN2 reactions?

SN2 reactions proceed with inversion of configuration at the carbon center.

What is the significance of halogen bonding in haloalkanes

Halogen bonding influences the physical properties and reactivity of haloalkanes.

What is the Friedel-Crafts alkylation reaction?

The reaction of haloalkanes with benzene in the presence of AlCl3 to form alkylbenzenes.

How are polyhalogenated compounds formed?

By successive halogenation of hydrocarbons.

What is the role of polar aprotic solvents in nucleophilic substitution reactions?

They enhance the nucleophilicity of the nucleophile, increasing the reaction rate.

How can haloarenes be converted to phenols?

By reacting them with aqueous NaOH under high temperature and pressure.