3.2 Synthesis a

Question 1

What is bond fission?

Answer 1

the process of bond breaking

Question 2

What happens when organic reactions take place?

Answer 2

• bods in the reactant molecules are broken and
• bonds in the product molecule are made

Question 3

What are the two different types of bond fission?

Answer 3

• homolytic
• heterolytic

Question 4

What does homolytic fission result in?

Answer 4

the formation of two neutral radicals

Question 5

When does homolytic fission happen?

Answer 5

• normally occurs when non-polar covalent bonds are broken

Question 6

What does homolytic fission mean?

Answer 6

when each atom retains one electron from the sigma covalent bond and the bond breaks evenly

Question 7

Explain the suitability of reactions involving homolytic fission for organic synthesis

Answer 7

Reactions involving homolytic fission tend to result in the formation of very complex mixtures of products, making them unsuitable for organic synthesis.

Question 8

What is heterolytic fission?

Answer 8

occurs when one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly

Question 9

What does heterolytic fission result in?

Answer 9

the formation of two oppositely charged ions

Question 10

When does heterolytic fission happen?

Answer 10

normally when polar covalent bonds are broken

Question 11

Explain the suitability of reactions involving heterolytic fission for organic synthesis

Answer 11

Reactions involving heterolytic fission tend to result in far fewer products than reactions
involving homolytic fission, and so are better suited for organic synthesis.

Question 12

Explain the rules of curly arrows

Answer 12

• a single-headed arrow indicates the movement of a single electron
• a double-headed arrow indicates the movement of an electron pair
• the tail of the arrow shows the source of the electron(s)
• the head of the arrow indicates the destination of the electron(s)
• two single-headed arrows starting at the middle of a covalent bond indicate homolytic
  bond fission is occurring
• a double-headed arrow starting at the middle of a covalent bond indicates heterolytic
  bond fission is occurring
• an arrow drawn with the head pointing to the space between two atoms indicates that a
  covalent bond will be formed between those two atoms

Question 13

What is the use of curly arrows?

Answer 13

to represent the movement of electrons during bond fission and bond making

Question 14

What are attacking groups in heterolytic bond fission classified as?

Answer 14

• electrophiles
• nucleophiles

Question 15

What are nucleophiles?

Answer 15

• negatively charged ions or neutral molecules that are electron rich, such as
  Cl- , Br- , OH- , CN-
  , NH3 and H2O
• attracted towards atoms bearing a partial positive or full positive charge
• capable of donating an electron pair to form a new covalent bond

Question 16

What are electrophiles?

Answer 16

• positively charged ions or neutral molecules that are electron deficient, such as H+, NO2+ and SO3
• attracted towards atoms bearing a partial negative or full negative charge
• capable of accepting an electron pair to form a new covalent bond