6.1.1 Chemistry

Question 1

What is a leaving group (LG)?

Answer 1

A leaving group is an atom or group that can depart with an electron pair, typically more electronegative than carbon, allowing it to pull away the electron pair.

Question 2

What is required for a species to be a good leaving group?

Answer 2

A good leaving group must be able to accept both electrons from the bond it breaks (typically with a carbon atom) and be more electronegative than carbon. It is often either neutral or positively charged.

Question 3

What happens to a positively charged leaving group once it departs?

Answer 3

A positively charged leaving group becomes neutral once it departs by taking an electron pair from the bond.

Question 4

What are the typical characteristics of a leaving group (LG)?

Answer 4

LG is attached to an electrophilic carbon atom.

LG is more electronegative than carbon.
LG is either neutral or positively charged.
The bond to the LG is not excessively strong (e.g., C-F bond is too strong, so F is not a good LG).

Question 5

What is a carbocation?

Answer 5

A carbocation is an intermediate species where a carbon atom carries a positive charge. It is planar about the positive center and can be attacked from either side by nucleophiles.

Question 6

Why does a carbocation lose stereochemistry?

Answer 6

A carbocation is planar, so nucleophiles can attack from either side with equal probability, resulting in a 50/50 split of products and loss of stereochemistry.

Question 7

How does the substitution of carbon atoms affect the stability of carbocations?

Answer 7

More substituted carbocations (those with more carbon atoms attached) are more stable.

Question 8

What are electron-poor substrates?

Answer 8

Electron-poor substrates are molecules that can accept an electron pair to form a new bond and are attacked by nucleophiles. The electrophilic atom is the one with a full or partial positive charge.

Question 9

What are electron-rich substrates?

Answer 9

Electron-rich substrates have double bonds (either aromatic or non-aromatic) that can donate electrons to attack electrophiles.

Question 10

What is aromatic stabilization?

Answer 10

Aromatic stabilization occurs because the electrons in aromatic rings are delocalized, making these rings more stable and less reactive than expected. Reactions that destroy aromaticity are strongly disfavored.

Question 11

How do aromatic rings react compared to non-aromatic double bonds?

Answer 11

Aromatic rings resist addition reactions due to stabilization and can only undergo substitution reactions under extreme conditions. Non-aromatic double bonds are less stable and more prone to addition reactions.

Question 12

Why do non-aromatic double bonds undergo addition reactions more easily?

Answer 12

Non-aromatic double bonds lack the extra stabilization of delocalized electrons and are therefore more susceptible to addition reactions.

Question 13

What is an electrophilic reagent?

Answer 13

An electrophilic reagent is an electron-poor species that can accept an electron pair to form a new bond.

Question 14

What are the three types of electrophilic reagents?

Answer 14

Positively charged.
Species with a permanent partial charge (δ+).
Polarisable species that can develop a temporary partial charge (δ+) when near an electron-rich species.

Question 15

What are bases and nucleophiles?

Answer 15

Both are electron-rich species. Bases have an affinity for H atoms (abstracting them), while nucleophiles donate electrons to form bonds with electron-poor atoms.

Question 16

What is a base?

Answer 16

A base is an electron-rich species that removes (abstracts) a hydrogen atom, indicating it has an affinity for H atoms.

Question 17

What is a nucleophile?

Answer 17

A nucleophile is an electron-rich species that donates electrons to an electron-poor atom to form a bond.

Question 18

What are the different types of electron-rich species?

Answer 18

A non-nucleophilic base.
A nucleophile with low or no basicity.
A basic nucleophile.

Question 19

How do negatively charged nucleophiles compare to uncharged nucleophiles?

Answer 19

Negatively charged nucleophiles are stronger than uncharged nucleophiles.

Question 20

How does steric hindrance affect nucleophilic strength?

Answer 20

Increased steric hindrance near the nucleophilic atom decreases nucleophilic strength but has little effect on basicity, possibly increasing it.

Question 21

How are radicals generated?

Answer 21

Radicals can be generated through two methods:

UV light.
Heating a radical initiator.

Question 22

What are the two types of radical reactions?

Answer 22

Radical addition to an alkene.
Radical substitution with an alkane.

Question 23

What are the three stages of a radical reaction?

Answer 23

Initiation: Radicals are generated from non-radical starting materials, increasing the number of radicals.

Propagation: Radicals react with non-radicals, maintaining the number of radicals.

Termination: Two radicals react to form non-radical products, reducing the number of radicals.

Question 24

What are non-polar solvents, and what do they dissolve?

Answer 24

Non-polar solvents, such as hydrocarbons, have negligible differences in electronegativity between atoms and are best suited for dissolving non-polar species.

Question 25

What are polar-protic solvents?

Answer 25

Polar-protic solvents can form hydrogen bonds with other species, stabilizing them in the solution.

Question 26

What are polar-aprotic solvents?

Answer 26

Polar-aprotic solvents cannot form hydrogen bonds and rely on weak interactions to solvate other species.