Bonds and Reactions Flashcards
What are the two types of bond?
Sigma bond - hybrid orbitals
Pi bond - formed by over lap of p-orbitals
When covalent bonds are redistributed what can happen to the electrons?
Homolytic bond cleavage - a pair of valence electrons are split up, producing free radicals (unpaired e- in outer shell)
Heterolytic bond cleavage - a pair of valence electrons move together, remaining as a pair
Name some reactions:
Free radical substitution Nucleophilic substitution Electrophilic substitution Electrophilic addition - Hydration Elimination - Dehydration Condensation Hydrolysis
What is free radical substitution?
Initiation - where homolytic bond fission takes place
Propagation - where free radicals are used up and regenerated
Termination - the combining of free radicals
What is nucleophilic substitution?
A nucleophile - has an electron pair to donate
Substitution - an atom or group or atoms are replaced
What is electrophilic substitution?
Takes place with an aromatic ring
Electrophile - good at accepting an electron pair
The molecule can be partially positively charged with empty orbitals
Substitution - an atom or group or atoms are replaced
What is electrophilic addition?
Electrophile - good at accepting an electron pair
The molecule can be partially positively charged with empty orbitals
Addition - Where 2 or more molecules join together by breaking the π bond to form a single product
An atom or group of atoms is added to a reactant
Alkene -> alkane
What is hydration?
Electrophilic addition but the reactant added is water
What is elimination?
A molecule loses some of its components
What is dehydration?
Elimination when water is removed
A -> B + H2O
What is condensation reaction?
2 reactants are added together and a small molecule is eliminated
Such as H2O
A + B -> AB + H2O
What is hydrolysis?
The addition of water to break up a molecule - the reverse of condensation
AB + H2O -> A + B
What are examples of condensation and hydrolysis reactions?
Peptide bond formation
DNA/RNA polymerisation
ATP synthesis
Fats being stored/used
How do we define redox reactions?
OIL RIG
Oxidation is loss (of electrons)
Reduction is gain (of electrons)
O = loss of H R = gain of H
What is a transition state?
The point of highest energy in the chemical reaction
The bonds ‘bend back’ moving away from the molecule being attacked
It doesn’t really exist - just something we use to visualise
