Haloalkanes / Alkyl Halides – Exam Review

25 question-and-answer flashcards covering definitions, classification, preparation, mechanisms, physical and chemical properties, and key rules related to haloalkanes.

What is a haloalkane (alkyl halide)?

An organic compound derived from an alkane by replacing one or more hydrogen atoms with halogen atoms (F, Cl, Br, I).

What is the general molecular formula for a monohaloalkane?

CₙH₂ₙ₊₁X (or R–X), where X = F, Cl, Br, or I.

How is a primary (1°) haloalkane defined?

The carbon bearing the halogen is attached to only one other carbon atom (general formula RCH₂–X).

How is a secondary (2°) haloalkane defined?

The carbon bearing the halogen is attached to two other carbon atoms (general formula R₂CH–X).

How is a tertiary (3°) haloalkane defined?

The carbon bearing the halogen is attached to three other carbon atoms (general formula R₃C–X).

What is the difference between geminal and vicinal dihalides?

Geminal dihalides have both halogen atoms on the same carbon; vicinal dihalides have halogens on adjacent carbons.

State Markovnikov's rule for addition of HX to alkenes.

When HX adds to an unsymmetrical alkene, hydrogen bonds to the carbon with more hydrogens, while the halogen bonds to the carbon with fewer hydrogens.

What is the anti-Markovnikov (peroxide) effect observed with HBr?

In the presence of organic peroxides, HBr adds so that Br bonds to the carbon bearing more hydrogens, opposite to Markovnikov orientation.

Why does HBr, but not HCl or HI, exhibit the peroxide effect?

HCl’s strong bond resists radical formation, while HI radicals recombine rapidly; only HBr forms radicals at a suitable rate for free-radical addition.

What is Lucas reagent and what is it used for?

A mixture of conc. HCl and anhydrous ZnCl₂, used to convert primary/secondary alcohols to chloroalkanes (Groove’s process).

During alcohol → haloalkane conversion with HX, what is the order of acid reactivity?

HI > HBr > HCl.

Which substitution mechanism is favored by tertiary haloalkanes?

SN1, because a stable tertiary carbocation can form.

What stereochemical outcome characterizes an SN2 reaction?

Walden inversion—complete inversion of configuration at the reactive carbon.

In radical halogenation of alkanes, which C–H bonds are most readily substituted?

Tertiary > secondary > primary, reflecting radical stability.

State Saytzeff's (Zaitsev's) rule in dehydrohalogenation.

The major product is the more substituted (more alkyl-substituted) alkene formed fastest.

What is the reactivity order of alkyl halides toward nucleophilic substitution?

R–Cl < R–Br < R–I (reactivity increases down the group).

Arrange the halogens in order of reactivity toward radical halogenation of alkanes.

F₂ > Cl₂ > Br₂ > I₂.

Which reaction synthesizes ethers from haloalkanes and sodium alkoxides?

Williamson ether synthesis.

What is produced when two molecules of an alkyl halide react with sodium in dry ether (Wurtz reaction)?

A higher alkane with twice the carbon atoms (R–R) plus 2 NaX.

How does branching affect the boiling point of isomeric haloalkanes?

More branching lowers the boiling point by reducing surface area and van der Waals forces.

Which reagent is preferred to prepare pure chloroalkanes from alcohols and why?

Thionyl chloride (SOCl₂) with pyridine; SO₂ and HCl by-products escape as gases, giving a pure product (Darzen’s reaction).

Give an example of an ambident nucleophile discussed in the notes.

Cyanide ion (CN⁻), which can attack through carbon (nitrile) or nitrogen (isonitrile).

On which concentration(s) does the rate of an SN1 reaction depend?

Only on the concentration of the alkyl halide (unimolecular rate-determining step).

Which type of haloalkane reacts fastest in dehydrohalogenation with alcoholic KOH?

Tertiary > secondary > primary haloalkanes.

What oxidizing agent is added during iodination of alkanes to remove HI and drive the reaction forward?

Nitric acid (HNO₃).