Chapter 10: Radical Reactions

Question 1

What is an Ionic Reaction?

Answer 1

are those in which covalent bonds break heterolytically and in which ions are involved as reactants, intermediates or products

Question 2

What does Heterolytically mean?

Answer 2

When the bonding electron pair is split unevenly between the product, usually produces at least one ion

Question 3

What is Homolysis?

Answer 3

is the chemical bond disociation of a molecule by a process where each of the fragments retains one of the originally bonded electrons

Question 4

What are Free Radicals or (Radicals)?

Answer 4

mechanism that involve homolysis of covalent bonds with the production of intermediates possessing unpaired electrons called free radicals (radicals)
- almost all small radicals are short-lived, highly reactive species

Question 5

What does a single-barbed curved arrow mean?

Answer 5

sed to represent the movement of a single electron

Question 6

What is Hydrogen Abstraction?

Answer 6

gives the halogen atom an electron (from the hydrogen atom) to pair with its unpaired electron

Question 7

What is Radical Halogenation?

Answer 7

Alkanes react with molecular halogens to produce alkyl halides via a substitution reaction called radical halogenation
R-H +X2 –> R-X + HX
X = F, Cl, Br ; Iodine is essentially unreactive due to unfavourable reaction energies

Question 8

What is Chlorination?

Answer 8

adding of chlorine to an alkane

• chlorination of most higher alkanes gives a mixture of isomeric monochlorinated products as well as more highly halogenated compounds
• not useful as synthetic methods when the goal is preparation of a specific alkyl chloride

Question 9

Chlorine is what?

Answer 9

Chlorine is relatively unselective; it does not discriminate greatly among the different types of hydrogen atoms (primary,secondary, tertiary) in an alkane

Question 10

Bromine is generally less what?

Answer 10

Bromine is generally less reactive towards alkanes than chlorine, and bromine is more selective in the site of attack when it does react

Question 11

Chlorination of Methane: Mechanism of Reaction?

Answer 11

1. The reaction is promoted by heat or light (temperatures greater than 100°C)
   - Step 1: halogen dissociation (under the influence of heat/light a molecule of chlorine dissociates; takes one bonding electron)
2. The light-promoted reaction is highly efficient (small photons permits the formation of relatively large amounts of chlorinated product)
   - Step 2: Hydrogen Abstraction (A chlorine atom abstracts a hydrogen atom from a methane molecule)
   - Step 3: Halogen Abstraction (A methyl radical abstracts a chlorine atom from a chlorine atom)

Question 12

What is Chain Termination?

Answer 12

Coupling of any two radicals depletes the supply of reactive intermediates and terminates the chain

Question 13

What is a Chain Reaction?

Answer 13

This type of sequential, stepwise mechanism, in which each step generates the reactive intermediate that causes the next cycle of the reaction to occur is called a chain reaction

Question 14

Step 1 of Chlorination of Methane is also known as what?

Answer 14

Chain Initiating step: creation of radicals

Question 15

Step 2 of Chlorination of Methane is also known as what?

Answer 15

Chain Propagation: reaction and regeneration of radicals

Question 16

What is the Geometry of Alkyl Radicals?

Answer 16

The geometric structure of most alkyl radicals is trigonal planar at the carbon having the unpaired electron
- This structure can be accommodated by sp2-hybridized central carbon

Question 17

What does racemic form mean?

Answer 17

when achiral molecules react to produce a compound with a single tetrahedral chirality centre the product will be a racemic form

Question 18

What does a single barbed arrow represent?

Answer 18

it represents the direction of a single electron

Question 19

What are peroxides?

Answer 19

Peroxides are radicals that can produce alkyl radicals (ROOR –> 2RO)

Question 20

What is Bond Energy?

Answer 20

Formation of a more stable molecule such as H2 will yield an exothermic reaction

• On the contrary, breaking a bond will lead to an endothermic reaction
• Endothermic reactions will have a higher activation energy than the heat of reaction

Question 21

What does Lower Activation Energy mean?

Answer 21

Lower Activation Energy means that the reactants can be converted to products in a shorter period of time

Question 22

What is the General Rule?

Answer 22

If bonds are broken, the activation energy will be above zero

Question 23

Alkyl Radical Reactions are what?

Answer 23

Are sp2 hybridized

- The molecule starts off to be achiral, but after addition of chlorine, it will generate a racemic mixture (+/-)

Question 24

Reactions are more favourable in what kind of solvents?

Answer 24

They are more favourable in non polar solvents