Haloalkanes and Haloarenes Lecture Notes

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What results from the replacement of hydrogen in hydrocarbons by halogens?

The formation of alkyl halides (haloalkanes) and aryl halides (haloarenes).

What type of carbon do haloalkanes contain halogen atoms attached to?

sp3 hybridised carbon atoms of an alkyl group.

What type of carbon do haloarenes contain halogen atoms attached to?

sp2 hybridised carbon atoms of an aryl group.

What is chloramphenicol used for?

It is an antibiotic effective for the treatment of typhoid fever.

What hormone produced by our body contains iodine?

Thyroxine.

What disease is caused by the deficiency of thyroxine?

Goiter.

What is chloroquine used for?

It is used for the treatment of malaria.

What is halothane used for?

It is used as an anaesthetic during surgery.

Which compounds are being considered as potential blood substitutes in surgery?

Certain fully fluorinated compounds.

What can you name haloalkanes and haloarenes according to?

The IUPAC system of nomenclature.

How are haloalkanes classified based on the number of halogen atoms?

They can be classified as mono, di, or polyhalogen compounds.

What is a primary alkyl halide?

An alkyl halide where the halogen is attached to a primary carbon atom.

What are allylic halides?

Compounds where halogen is bonded to an sp3 hybridised carbon adjacent to a carbon-carbon double bond.

What are vinylic halides?

Compounds where the halogen atom is bonded to an sp2-hybridised carbon of a carbon-carbon double bond.

What is the common name derived from for alkyl halides?

Naming the alkyl group followed by the name of the halide.

How are dihalogen derivatives of benzene named in IUPAC nomenclature?

Using numerals 1,2; 1,3; and 1,4 instead of prefixes o-, m-, p-.

What are geminal halides?

Dihalides where both halogen atoms are on the same carbon atom.

What are vicinal halides?

Dihalides where halogen atoms are on adjacent carbon atoms.

How does the carbon-halogen bond behave across different halogens?

The bond length increases down the group from fluorine to iodine.

What factors affect the preparation of alkyl halides from alcohols?

The presence of catalysts and the nature of alcohols (primary, secondary, tertiary).

Which method gives pure alkyl halides with thionyl chloride?

The reaction of alcohol with thionyl chloride produces alkyl halide along with SO2 and HCl, which escape.

In free radical halogenation, what is a major challenge?

It produces a complex mixture of isomeric mono- and polyhaloalkanes.

What is Markovnikov’s rule related to?

The addition of hydrogen halides to alkenes with the predominant product being determined by the most stable carbocation.

What reaction is the Finkelstein reaction?

The reaction of alkyl chlorides or bromides with NaI in dry acetone to form alkyl iodides.

What is the Swarts reaction?

Heating alkyl chloride/bromide in the presence of metallic fluorides to form alkyl fluorides.

How can aryl halides be prepared?

By electrophilic substitution of arenes with chlorine or bromine, using Lewis acids as catalysts.

Why are aryl halides less reactive in nucleophilic substitution?

Due to resonance effects and partial double bond character of C-X bonds.

What are ambident nucleophiles?

Nucleophiles that can react through two different atoms.

What is the major reaction pathway for secondary alkyl halides?

They can undergo either SN1 or SN2 mechanisms depending on conditions.

What is the expected result when a chiral alkyl halide undergoes SN2 reaction?

Inversion of configuration.

How does the order of reactivity for SN1 reactions compare to SN2?

SN1 reactivity follows the order: tertiary > secondary > primary; SN2 follows: primary > secondary > tertiary.

What is a racemic mixture?

A mixture containing equal amounts of two enantiomers, resulting in no net optical activity.

What leads to the stability of carbocations in SN1 reactions?

The stability increases with the degree of alkyl substitution.

What characterizes the elimination mechanism in haloalkanes?

Elimination occurs from β-hydrogens, typically forming alkenes.

What is the main type of bond formed in organo-metallic compounds?

Carbon-metal bonds.

What is the significance of Grignard reagents?

These are highly reactive organo-metallic compounds used in various organic syntheses.

What are the physical properties of haloalkanes compared to hydrocarbons?

Haloalkanes generally have higher boiling points due to dipole-dipole interactions.

Why are haloalkanes immiscible with water?

Water forms stronger hydrogen bonds than those created between water and haloalkanes.

What is the effect of sequential substitution on optical activity?

Sequential substitution can lead to inversion, retention, or racemisation at chiral centers.

Why are polyhalogen compounds a concern for the environment?

They can persist and contribute to ozone depletion and other environmental hazards.

How does the presence of nitro groups affect the reactivity of haloarenes?

Nitro groups at ortho and para positions increase reactivity towards nucleophilic substitution.

What is the major product of elimination reactions in terms of alkene stability?

The more substituted alkene is typically the major product, following Zaitsev's rule.

What is DDT, and why is it controversial?

DDT is a chlorinated insecticide; it is effective but has led to environmental issues and bans.

What are the primary uses of Dichloromethane?

It's used as a solvent in various industrial applications, including paint removal.

What happens when chloroform is used improperly?

Improper exposure can cause central nervous system depression and other health effects.

What is a primary use for Freon compounds?

Freon compounds are used as refrigerants and aerosol propellants.

What types of reactions do haloalkanes typically undergo?

Nucleophilic substitution, elimination reactions, and reactions with metals to form organometallic compounds.

How do physical properties of haloalkanes affect their industrial applications?

Their polarity and boiling points make them suitable solvents and reactive intermediates.

What factors influence the outcome of nucleophilic substitution reactions?

The nature of the alkyl halide, the nucleophile, and the reaction conditions.

What are the characteristics of SN1 and SN2 reactions?

SN1 involves carbocation formation with racemisation, while SN2 involves a concerted mechanism with inversion.

How do resonance effects influence the reactivity of haloarenes?

They stabilize the C-X bond making it harder to break during nucleophilic substitution.

What are the environmental impacts of certain polyhalogen compounds?

They can contribute to ozone depletion and have harmful biological effects.