10. Electron-pair sharing reactions

What is a nucleophile?

An electron-rich species that donates a pair of electrons to an electrophile.

What are the two types of nucleophiles?

• Neutral nucleophiles (e.g., NH₃, H₂O).

• Negatively charged nucleophiles (e.g., OH⁻, CN⁻).

What is the role of a nucleophile in a reaction?

It donates electrons to form a covalent coordination bond with an electrophile.

What determines the strength of a nucleophile?

Its ability to donate an electron pair.

What must be present in a nucleophile?

A lone pair of electrons.

How do nucleophilic substitution reactions work?

A nucleophile replaces a leaving group in an electrophile, forming a new compound.

Why are halogenoalkanes susceptible to nucleophilic attack?

The electronegative halogen creates a partial positive charge on the carbon atom.

What is heterolytic fission?

A bond-breaking process where one atom takes both bonding electrons.

What are the products of heterolytic fission of a halogenoalkane?

A halide anion (X⁻) and a positively charged carbocation.

What type of arrow is used to show electron movement in heterolytic fission?

A double-barbed curly arrow.

What is a carbocation?

A positively charged carbon species formed after heterolytic fission.

What is an electrophile?

An electron-deficient species that accepts electron pairs from nucleophiles.

What are two types of electrophiles?

• Positively charged ions (cations) (e.g., CH₃⁺).

• Neutral molecules with a partial positive charge (e.g., BF₃).

Why is BF₃ an electrophile?

It has an electron-deficient boron atom, making it susceptible to nucleophilic attack.

Why are alkenes more reactive than alkanes?

The double bond creates a region of high electron density, attracting electrophiles.

What is an electrophilic addition reaction?

A reaction where an electrophile adds across a carbon–carbon double bond.

How does bromine react with ethene?

It forms 1,2-dibromoethane via an electrophilic addition reaction.

What is the bromine water test used for?

To detect unsaturated compounds (alkenes/alkynes); bromine water turns colorless.

How can iodine detect unsaturation in hydrocarbons?

A color change from yellow/brown/purple to colorless occurs when iodine reacts with an alkene.

What is the product when propene reacts with Cl₂?

• 1,2-dichloropropane.

What is the product of but-2-ene reacting with HBr?

A monosubstituted halogenoalkane.

What is the product of adding water to an alkene in an acidic solution?

An alcohol.

What is the electrophilic addition product of hex-3-ene with water?

Hexan-3-ol.

Covalent Coordination Bond

• A bond formed when a nucleophile donates electrons to an electrophile.

Electrophilic Addition

A reaction where an electrophile adds across a C=C double bond.

Hydrohalogenation

The addition of a hydrogen halide (HCl, HBr) across a double bond in an alkene.

Hydration Reaction

The addition of water (H₂O) to an alkene to form an alcohol.

Markovnikov’s Rule

In hydrohalogenation, the hydrogen atom adds to the carbon with more hydrogen atoms.