Reactivity 3.4 — HL

Question 1

What is the definition of a Lewis acid and a Lewis base in chemistry?

Answer 1

A Lewis acid is a substance that can accept a pair of electrons, while a Lewis base is a substance that can donate a pair of electrons.

Question 2

How does the Lewis acid-base theory differ from the Brønsted-Lowry acid-base theory?

Answer 2

The Lewis theory focuses on the transfer of electron pairs, while the Brønsted-Lowry theory focuses on the transfer of protons.

Question 3

Provide an example of a Lewis acid and a Lewis base reaction.

Answer 3

AlCl3 reacting with H2O to form Al(OH)3 and HCl. AlCl3 acts as the Lewis acid (electron pair acceptor), and H2O acts as the Lewis base (electron pair donor).

Question 4

Explain why water can act as both a Lewis acid and a Lewis base.

Answer 4

Water can act as a Lewis base by donating a pair of electrons and as a Lewis acid by accepting a pair of electrons, making it amphoteric.

Question 5

Can all Brønsted-Lowry acids be considered Lewis acids? Provide reasoning.

Answer 5

Yes, all Brønsted-Lowry acids can be considered Lewis acids because they are capable of accepting an electron pair due to their ability to donate protons.

Question 6

What defines a coordination bond in a coordination complex?

Answer 6

A coordination bond is formed when a pair of electrons from a Lewis base (ligand) is donated to a Lewis acid (metal ion), resulting in a complex ion or molecule.

Question 7

How can you determine the charge on a complex ion?

Answer 7

To determine the charge on a complex ion, sum the charges of the central metal ion and the charges of all ligands, then account for the overall charge of any counterions present in the complex.

Question 8

What role do ligands play in the formation of a coordination complex?

Answer 8

Ligands act as Lewis bases by donating a pair of electrons to the central metal ion (Lewis acid), forming coordination bonds and stabilizing the complex ion.

Question 9

Can coordination complexes exhibit isomerism, and if so, what types?

Answer 9

Yes, coordination complexes can exhibit both structural isomerism (different bond connections among atoms) and stereoisomerism (different spatial arrangements of atoms), including geometric and optical isomers.

Question 10

How does the coordination number affect the geometry of a coordination complex?

Answer 10

The coordination number, or the number of ligands bonded to the central metal ion, directly influences the geometry of a coordination complex, determining its shape (e.g., octahedral, tetrahedral, square planar).

Question 11

What is the SN2 reaction mechanism and how does it differ from SN1?

Answer 11

SN2 involves a single-step process where the nucleophile attacks the substrate, leading to simultaneous bond formation and bond breaking. It differs from SN1, which occurs in two steps, involving carbocation intermediate formation followed by nucleophilic attack.

Question 12

How does steric hindrance affect the rate of SN2 reactions?

Answer 12

Steric hindrance slows down SN2 reactions because bulky groups around the reactive center obstruct the approach of the nucleophile, making the reaction less likely to occur.

Question 13

What is the effect of the substrate’s structure on the preference for SN2 or SN1 mechanisms?

Answer 13

The substrate’s structure significantly influences the mechanism; primary halides favor SN2 due to less steric hindrance, while tertiary halides favor SN1 due to the stability of the carbocation intermediate.

Question 14

How do nucleophiles influence the rate of nucleophilic substitution reactions?

Answer 14

Stronger nucleophiles increase the rate of nucleophilic substitution reactions by more effectively donating electron pairs, especially in SN2 mechanisms where the reaction rate is directly related to nucleophile strength.

Question 15

Describe the stereochemical outcome of an SN2 reaction.

Answer 15

SN2 reactions result in the inversion of configuration at the carbon center where the reaction occurs, due to the backside attack mechanism, leading to a mirror image of the original stereochemistry.

Question 16

What initiates the electrophilic addition reaction in alkenes?

Answer 16

The reaction initiates when the electron-rich double bond of an alkene attacks an electrophile, leading to the formation of a carbocation intermediate.

Question 17

How does the Markovnikov’s rule apply to the electrophilic addition of hydrogen halides to alkenes?

Answer 17

Markovnikov’s rule states that in the addition of hydrogen halides to alkenes, the hydrogen atom bonds to the carbon with the greater number of hydrogen atoms, leading to the more stable carbocation intermediate.

Question 18

Explain the role of carbocation stability in determining the major product of electrophilic addition reactions.

Answer 18

The stability of the carbocation intermediate affects the reaction’s outcome; more stable carbocations lead to the major product because they are lower in energy and form more readily.

Question 19

Describe the electrophilic addition reaction of water to alkenes to form alcohols.

Answer 19

Water reacts with alkenes in the presence of a strong acid catalyst, leading to the formation of alcohols. The reaction involves the formation of a carbocation intermediate and follows Markovnikov’s rule.

Question 20

What is the significance of regioselectivity in electrophilic addition reactions of unsymmetrical alkenes?

Answer 20

Regioselectivity determines the direction of bond formation in unsymmetrical alkenes, influenced by factors such as carbocation stability, leading to the predominant formation of one product over possible alternatives.

Question 21

Describe the general mechanism of an electrophilic substitution reaction with benzene.

Answer 21

The reaction starts with the attack of an electrophile on the electron-rich benzene ring, forming a carbocation intermediate. This is followed by the loss of a hydrogen ion, restoring the aromaticity of the benzene ring.

Question 22

What makes benzene less prone to undergo addition reactions despite its unsaturation?

Answer 22

Benzene’s stability is due to the delocalization of π electrons across the ring, making it more stable and less reactive towards addition reactions that would disrupt this delocalization.

Question 23

How does the nitration of benzene occur and what does it produce?

Answer 23

Nitration of benzene occurs via the reaction of benzene with nitric acid in the presence of sulfuric acid, producing nitrobenzene. The sulfuric acid protonates nitric acid, forming the nitronium ion, which acts as the electrophile.

Question 24

What is the role of a catalyst in the electrophilic substitution reaction of benzene?

Answer 24

A catalyst, such as FeBr3 in bromination, provides a more reactive form of the electrophile, facilitating the formation of the carbocation intermediate and thus the substitution reaction.

Question 25

Explain the concept of regioselectivity in electrophilic substitution reactions of benzene when multiple substituents are present.

Answer 25

Regioselectivity refers to the preference for substitution at specific positions on the benzene ring, influenced by the electronic effects of existing substituents, such as activating or deactivating groups, and their directing effects on incoming electrophiles.