Electron Pair Sharing Reactions (DP IB Chemistry)

True.

Haloalkanes will undergo nucleophilic substitution reactions due to the polar C-X bond (where X is a halogen).

Heterolytic fission is the breakage of a covalent bond when both bonding electrons remain with one of the two fragments formed.

In heterolytic fission, a double-headed arrow is used to show the movement of a pair of electrons.

In the following mechanism, H⁺ is acting as an electrophile.

In the following mechanism OH^- is acting as a nucleophile.

An electrophile is an electron-deficient species that can accept a pair of electrons.

The mechanism shows heterolytic fission as the more electronegative atom takes both the electrons from the bond to form a negative ion and leaves behind a positive ion.

An electrophilic addition reaction is the addition of an electrophile to an alkene double bond, C=C

Examples of neutral electrophiles include:

• HX (hydrogen halides)

• X₂ (halogens)

• H₂O

• RX (halogenoalkanes)

Examples of charged electrophiles include:

• H⁺

• NO₂⁺

• NO⁺

• R⁺

Propene reacts with steam to form propanol.

Propene reacts with HCl to form chloropropane .

True.

Halogens, X₂, react with alkenes to form dihalogenoalkanes.

Alkenes are susceptible to electrophilic attack because of the high electron density of the carbon–carbon double bond

The product formed by the reaction between propene and bromine is:

A Lewis acid is an electron pair acceptor.

A Lewis base is an electron pair donor.

OH^- ions act as Lewis bases.

True.

CN^- ions can act as Brønsted-Lowry bases and Lewis bases.

In the following reaction, A⁺ is acting as a Lewis acid.

A⁺ + :B^- → AB

In the following reaction, :B^- is acting as a Lewis base.

A⁺ + :B^- → AB

NH₃ can act as a Lewis base because it can donate it's lone pair of electrons / electron pair.

False.

H⁺ can behave as a Lewis acid as it can accept an electron pair.

When ammonia, NH₃, and boron trifluoride, BF₃, react, a coordinate bond is formed.

BF₃ is acting as a Lewis acid.

NH₃ is acting as a Lewis base.

An electrophile behaves as a Lewis acid.

An nucleophile behaves as a Lewis base.

In the following complex, Cu²⁺ is acting as a Lewis acid.

In the following complex H₂O is acting as a Lewis base.

A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond.

Monodentate ligands can form one co-ordinate bond to the central metal ion.

Coordination number is the number of co-ordinate bonds to the central metal atom or ion.

Bidentate ligands can form two co-ordinate bonds.

Three factors the charge of a complex ion depends upon are:

• The charge of the central metal ion

• The charge of the ligands

• The coordination number

The charge of copper in [CuCl₄]^2– is 2-.

The charge of iron in [Fe(H₂O)₆]²⁺ is 2+.

The charge of silver in [Ag(NH₃)₂]⁺ is 1+.

The coordination number in [Fe(H₂O)₆]³⁺ is 6.

The charge on the complex ion is [Cr(H₂O)₆]Cl₃ is 3+ . The chloride ion, Cl^-, outside the square brackets must balance against the charge on the complex, [Cr(H₂O)₆]³⁺.

The charge on the complex ion is [CrCl₂(H₂O)₄]Cl.2H₂O is 1+ . The chloride ion, Cl^-, outside the square brackets must balance against the charge on the complex, [CrCl₂(H₂O)₄]⁺.

S_N1 stands for Substitution Nucleophilic Unimolecular.

A carbocation is a carbon atom with a positive charge.

False.
The rate of an S_N1 reaction depends only on the concentration of the halogenoalkane.

The rate equation for an S_N1 reaction is rate = k[halogenoalkane].

Heterolytic fission is the breaking of a covalent bond where both electrons move to one of the atoms, forming an anion and a cation.

An S_N1 mechanism involves two steps.

Tertiary halogenoalkanes typically undergo S_N1 reactions.

Unimolecular means that the rate-determining step of the reaction involves only one molecule.

In the first step of an S_N1 reaction, a carbocation intermediate is formed.

True.

The energy profile diagram for an S_N1 reaction shows two curves.

S_N2 stands for Substitution Nucleophilic Bimolecular.

Bimolecular means that the rate-determining step of the reaction involves two molecules.

False. The rate of an S_N2 reaction depends on the concentration of both the halogenoalkane and the nucleophile.

The rate equation for an S_N2 reaction is rate = k[halogenoalkane][nucleophile].

Inversion of configuration is the process where the stereochemistry of a molecule is reversed during a reaction.

An S_N2 mechanism involves one step.

Primary halogenoalkanes typically undergo S_N2 reactions.

Steric hindrance is the prevention of a reaction due to the spatial arrangement of atoms in a molecule.

In an S_N2 reaction, the configuration of the molecule is inverted.

False. The energy profile diagram for an S_N2 reaction shows one curve.

Three factors that affect the rate of nucleophilic substitution are:

1. The nature of the nucleophile

2. The halogen involved (leaving group)

3. The structure (class) of the halogenoalkane.

The greater the electron density on the nucleophile ion or molecule, the stronger the nucleophile.

True.

Negative anions tend to be more reactive nucleophiles than their corresponding neutral species.

The electronegativity of the atom carrying the lone pair becomes the deciding factor. The less electronegative the atom, the stronger the nucleophile.

The nucleophiles in order of increasing strength:

H₂O < NH₃ < OH^- < CN^-

The weaker the carbon-halogen bond, the more reactive the halogenoalkane.

The halogenoalkanes in order of increasing reactivity are:

R-F < R-Cl < R-Br < R-I

Tertiary halogenoalkanes undergo S_N1 reactions.

Secondary halogenoalkanes undergo a mixture of S_N1 and S_N2 reactions.

Primary halogenoalkanes undergo S_N2 reactions.

The stability of carbocations increases from primary to tertiary due to the positive inductive effect of alkyl groups.

A nucleophile is a chemical species that donates an electron pair to form a chemical bond, acting as a Lewis base.

Electrophilic addition takes place when an electrophile adds across a double bond.

An electrophile is an electron pair acceptor.

True.

Water adds across the double bond in ethene in an electrophilic addition reaction.

Ni or Pt is the catalyst needed for the electrophilic addition of hydrogen to an alkene.

False.

Electrophilic addition of halogens and hydrogen halides occurs at room temperature.

The first step is the donation of an electron pair to the electrophile.

False.

In electrophilic addition, an electron pair is donated from the nucleophile to the carbocation.

False.

The curly arrow head points in the wrong direction. It should be:

Hydrogen halides have a permanent dipole.

True.

Water is a weak electrophile.

False

The step shown is the slow step of the mechanism.

A carbocation is a positively charged carbon atom with only three covalent bonds instead of four.

False.

The image shows a secondary carbocation. A tertiary carbocation should have three carbons attached to the central carbon.

The inductive effect is the process by which alkyl groups push electrons towards a positively charged carbon, making the carbocation less positively charged and more stable.

True.

Tertiary carbocations are the most stable as they have three electron-donating alkyl groups which energetically stabilise the carbocation.

Markovnikov's rule states that in an electrophilic addition reaction of a hydrogen halide, HX, to an alkene, the halogen ends up bonded to the most substituted carbon atom.

The major product in electrophilic addition reactions is determined by the formation of the most stable carbocation intermediate.

False.

Anti-Markovnikov addition favours the formation of the minor product.

The order of carbocation stability is:

tertiary > secondary > primary.

In step 1 of the electrophilic addition mechanism, a pair of electrons from the electrophile moves towards the electrophile.

False.

The nucleophile bonds to the positive carbon atom of the carbocation.

False.

The product shown is the minor product. The major product is the one in which the halogen joins onto the most substituted carbon, which is the middle carbon.

Nitration is the substitution of a hydrogen atom from the benzene ring with an electrophilic nitro (-NO₂) group.

Electrophilic substitution is a reaction where an electrophile replaces a hydrogen atom on an aromatic ring.

The three steps of electrophilic substitution in arenes are:

1. Generation of an electrophile

2. Electrophilic attack

3. Regenerating aromaticity.

An electrophile is a positive ion or the positive end of a polar molecule that is attracted to electron-rich areas.

True.

The nitronium ion (NO₂⁺) is the electrophile in benzene nitration.

The nitronium ion is produced in situ by adding a mixture of concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄) at a temperature between 25 and 60°C to the reaction mixture.

False.

During the electrophilic attack step, a pair of electrons from the benzene ring is donated to the electrophile to form a covalent bond.

Heterolytic cleavage is the breaking of a chemical bond where both electrons in the bond go to one of the atoms involved in the bond.

True.

The intermediate in the nitration of benzene is:

The purpose of the third step in electrophilic substitution is to restore the aromaticity of the benzene ring system.

False.

The arrow is the wrong way around, it should be: