Introduction to Organic Chemistry: Reaction Mechanisms Flashcards
1
Q
What are reaction mechanisms?
A
- Mechanisms break reactions down into a sequence of stages
- They show how molecules react together by using curly arrows to show which bonds are made or broken
2
Q
What is homolytic fission?
A
- X——Y → •X + •Y
- In homolytic fission, when the bond breaks each atom gains one of the shared pair of electrons
- Homolytic fission usually occurs when the atoms have the same/similar electronegativities
- Free radicals are species with an unpaired electron
- Free radicals are represented by a dot
3
Q
What is heterolytic fission?
A
- X——Y → X^+ + :Y‒
- In heterolytic fission, when the bond breaks one atom gains both of the shared pair of electrons
- Heterolytic fission usually occurs when the atoms have the different electronegativities
• Ions
- When the bond breaks both the shared pair of electrons go to the most electronegative atom
4
Q
What are curly arrows used to represent?
A
- We can show bond breaking and bond forming by using curly arrows
• Base of the arrow
- This shows where a pair of electrons come from
- This is always from either from:
- the centre of a bond
- a lone pair of electrons
• Head of the arrow
- This shows where the pair of electrons are going to
- Each arrow head tip represents an electron (always two electrons in A-level)
5
Q
How are curly arrows used to show bonds breaking?
A
- To show heterolytic fission the curly arrow originates from the centre of the bond
- X——Y → X^+ + :Y^‒
- Curly arrow goes from centre of bond to Y on same side of equation
- At A-level, curly arrows are not used in homolytic fission
6
Q
How are curly arrows used to show bonds forming?
A
- To show bond formation the curly arrow starts from either a lone pair of electrons or another covalent bond
- ^‒Y: X^+ → X——Y
- Curly arrow goes from electrons on Y to X^+
- X——Y Z+ → Y——Z + X^+
- Curly arrow goes from X-Y bond to Z^+
