chemistry - 4.2
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What happens when an organic reaction takes place?
Bonds in the reactant molecules are broken and bonds in the product molecules are made.
What is the process of bond breaking known as?
Bond fission.
What are the two types of bond fission?
Homolytic and heterolytic.
What does homolytic fission result in?
The formation of two neutral radicals.
When does homolytic fission occur?
When each atom retains one electron from the sigma covalent bond and the bond breaks evenly.
When does homolytic fission normally occur?
When non-polar covalent bonds are broken.
What do reactions involving homiletic fission tend to result in?
The formation of very complex mixtures of products, making them unsuitable for organic synthesis.
What does heterolytic fission result in?
The formation of two oppositely charged ions.
When does heterolytic fission occur?
When one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly.
When does heterolytic fission normally occur?
When polar covalent bonds are broken.
What do reactions involving heterolytic fission tend to result in?
Far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis.
How can the movement of electrons during bond fission and bond making be represented?
Using curly arrow notation.
What does a single-headed arrow indicate?
The movement of a single electron.
What does a double-headed arrow indicate?
The movement of an electron pair.
What does the tail of the arrow show?
The source of the electron(s).
What does the head of the arrow indicate?
The destination of the electron(s).
What do two single-headed arrows starting at the middle of a covalent bond indicate?
Homolytic bond fission is occurring.
What does a double-headed arrow starting at the middle of a covalent bond indicate?
Heterolytic bond fission is occurring.
What does an arrow drawn with the head pointing to the space between two atoms indicate?
That a covalent bond will be formed between those two atoms.
In reaction involving heterolytic bond fission, what are attacking groups classified as?
Nucleophiles or electrophiles.
What are nucleophiles?
Negatively charged ions or neutral molecules that are electron rich, such as Cl−, Br−, OH−, CN− , NH3 and H2O.
What are nucleophiles attracted towards?
Atoms bearing a partial or full positive charge.
What are nucleophiles capable of?
Donating an electron pair to form a new covalent bond.
What are electrophiles?
Positively charged ions or neutral molecules that are electron deficient, such as H+,NO+ and SO3.