Haloalkanes and Haloarenes Practice Flashcards

A set of practice flashcards covering the key concepts of Haloalkanes and Haloarenes, including nomenclature, classification, preparation methods, physical properties, and chemical reaction mechanisms like SN1 and SN2.

What results from the replacement of hydrogen atom(s) in an aliphatic hydrocarbon by halogen atom(s)?

Alkyl halide (haloalkane)

How is the carbon atom to which the halogen is attached hybridised in haloalkanes versus haloarenes?

In haloalkanes, the carbon is $sp^{3}$ hybridised; in haloarenes, the carbon is $sp^{2}$ hybridised.

What is the medical use for the chlorine-containing antibiotic chloramphenicol?

It is used for the treatment of typhoid fever.

What disease is caused by the deficiency of the iodine-containing hormone thyroxine?

Goiter

Which synthetic halogen compound is used for the treatment of malaria?

Chloroquine

Define allylic halides.

Compounds in which the halogen atom is bonded to an $sp^{3}$-hybridised carbon atom adjacent to a carbon-carbon double bond ($C=C$).

What are benzylic halides?

Compounds in which the halogen atom is bonded to an $sp^{3}$-hybridised carbon atom attached to an aromatic ring.

What is the difference between vinylic halides and aryl halides?

In vinylic halides, the halogen is bonded to an $sp^{2}$-hybridised carbon of a $C=C$ double bond; in aryl halides, the halogen is directly bonded to the $sp^{2}$-hybridised carbon of an aromatic ring.

Distinguish between geminal halides and vicinal halides.

In geminal halides (gem-dihalides), both halogen atoms are on the same carbon atom. In vicinal halides (vic-dihalides), halogen atoms are on adjacent carbon atoms.

In the context of the $C-X$ bond, why does the carbon bear a partial positive charge and the halogen bear a partial negative charge?

Halogen atoms are more electronegative than carbon, causing the bond to be polarised.

What is the trend for carbon-halogen bond length and bond enthalpy from $C-F$ to $C-I$?

Bond length increases ($C-F = 139\text{ pm}$, $C-I = 214\text{ pm}$) and bond enthalpy decreases ($C-F = 452\text{ kJ~mol}^{-1}$, $C-I = 234\text{ kJ~mol}^{-1}$).

Why is thionyl chloride ($SOCl_{2}$) preferred for preparing alkyl halides from alcohols?

Because the by-products ($SO_{2}$ and $HCl$) are escapable gases, leaving the alkyl halide in pure form.

What is the order of reactivity of alcohols with a given haloacid?

$$3^{\text{o}} > 2^{\text{o}} > 1^{\text{o}}$$

What is the Finkelstein reaction?

The preparation of alkyl iodides by the reaction of alkyl chlorides or bromides with $NaI$ in dry acetone.

What is the Swarts reaction?

The synthesis of alkyl fluorides by heating an alkyl chloride or bromide in the presence of a metallic fluoride such as $AgF$, $Hg_{2}F_{2}$, $CoF_{2}$, or $SbF_{3}$.

How are aryl chlorides and bromides prepared via electrophilic substitution?

By reaction of arenes with chlorine or bromine in the presence of Lewis acid catalysts like iron or iron(III) chloride.

What is Sandmeyer's reaction?

The replacement of a diazonium group in a diazonium salt with $-Cl$ or $-Br$ using cuprous chloride or cuprous bromide.

How do boiling points of alkyl halides change with the halogen atom for the same alkyl group?

The boiling points decrease in the order: $RI > RBr > RCl > RF$.

How does branching affect the boiling point of isomeric haloalkanes?

Boiling points decrease with increase in branching.

Why do para-isomers of dihalobenzenes have higher melting points than ortho- and meta-isomers?

Due to the symmetry of para-isomers, which allows them to fit better into the crystal lattice.

What characterizes an $S_{N}2$ (Substitution nucleophilic bimolecular) reaction?

It occurs in a single step with no intermediate, involves a transition state with five-coordinated carbon, and results in inversion of configuration.

What is the reactivity order of alkyl halides toward $S_{N}2$ reactions?

Primary halide > Secondary halide > Tertiary halide.

What characterizes an $S_{N}1$ (Substitution nucleophilic unimolecular) reaction?

It occurs in two steps via a carbocation intermediate; the rate depends only on the concentration of the alkyl halide.

What is the reactivity order of alkyl halides toward $S_{N}1$ reactions?

Tertiary halide > Secondary halide > Primary halide.

Define ambident nucleophiles.

Groups that possess two nucleophilic centres, such as cyanide ($CN^{-}$) and nitrite ($NO_{2}^{-}$) ions.

What are enantiomers?

Stereoisomers related to each other as non-superimposable mirror images.

What is a racemic mixture?

A mixture containing two enantiomers in equal proportions, resulting in zero optical rotation.

State Zaitsev (Saytzeff) rule.

In dehydrohalogenation reactions, the preferred product is the alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms.

What is a Grignard reagent?

An organo-metallic compound with the general formula $RMgX$, obtained by reacting haloalkanes with magnesium metal in dry ether.

What is the difference between the Wurtz reaction and the Fittig reaction?

The Wurtz reaction uses alkyl halides to form hydrocarbons with double carbon atoms; the Fittig reaction uses aryl halides to join two aryl groups together.

Why are aryl halides less reactive towards nucleophilic substitution than alkyl halides?

Due to resonance (partial double bond character of $C-X$), $sp^{2}$ hybridisation of carbon, instability of phenyl cation, and electronic repulsion.

What is Phosgene?

An extremely poisonous gas ($COCl_{2}$, carbonyl chloride) formed by the slow oxidation of chloroform by air in the presence of light.

What are Freons?

Chlorofluorocarbon compounds of methane and ethane that are stable, unreactive, and used as refrigerants and propellants.

What is the environmental impact of Carbon tetrachloride ($CCl_{4}$) when released into the air?

It rises to the atmosphere and depletes the ozone layer.

What is DDT and who discovered its effectiveness as an insecticide?

p,p'-Dichlorodiphenyltrichloroethane; its insecticidal properties were discovered by Paul Muller in 1939.