S2 Fulton L5-7 Flashcards
What does KIE stand for
Kinetic isotope effects
What doe kinetic isotope effects show
Kinetic isotope effects can tell us whether a particular bond is broken either before or during the RDS
Describe how we use the kinetic isotope effects
Consider C-H and C-D bonds. These bonds have the same chemical nature and they react in the same way. Because of different masses the bonds have different vibration frequencies and dissociation energies. The C-D is stronger bond and C-D will be slower to break. If a C-H bind is broken in the rate determining step, the rate of reaction should be slower when the C-D is broken
What experiment do we need to run to see if there is a KIE
Requires two experiments one using H and one using D. We then work out the rate constants from these two reactions and work out the value of kH/kD. A higher ratio between 2-8 suggests a primary KIE and supports the idea that C-H is broken in the RDS
What are isotopes exchange methods used for
Isotope exchange experiment can test for processes where there is fast reversible removal of a proton such as E1cB
What sort of reactions can KIE help us to distinguish between
Can help us distinguish between E1 and E2 mechanisms
How can isotope exchange establish the presence of the E1cB mechanism
In the E1cB mechanism, a carbanion intermediate is formed by removal of an acidic proton. If the reaction is run in D₂O and deuterium replaces hydrogen at the α-carbon before elimination occurs, this shows: The proton loss is reversible and The carbanion exists long enough to undergo isotopic exchange. This deuterium incorporation is strong evidence for the E1cB pathway,
Define a polymer
Polymers are large molecules made up of simple repeating units
What are polymers synthesised from
Polymers are synthesised from simple molecules called monomers
What is the process of polymer synthesis called
Polymerisation
What sort of bonds are monomers linked through
Covalent bonds
What does a molecule need to be considered a polymer
To be classed as a polymer, n is typically greater than 50. Anything less that 50 is considered an oligomer.
Define polymer architectures
polymer architecture - how the monomer units are arranged within the polymer chain.
List the different types of linear polymer architectures
Archetypical polymer
Alternating copolymer
Random copolymer
Block copolymer
What is an archetypical polymer
Made from only one type of monomer repeated throughout the chain.
What is an alternating copolymer
Two monomers alternate in a regular ABAB pattern.
What is a random copolymer
Two or more monomers are randomly distributed along the chain.
What is a block copolymer
Long, continuous segments (blocks) of one monomer followed by blocks of another.
List three different types of branched polymers
Hyperbranched polymers
Comb polymers
Dendrimers
What are hyperbranched polymers
Has a high degree of branching, but not perfectly symmetric.
What are comb polymers
A linear backbone with regularly spaced side chains (like teeth on a comb).
What are dendrimers
Highly branched, tree-like structure with perfect symmetry and layers (called generations).
Why is calculating polymer molecular weight not straightforward
because samples of synthetic polymers are heterogeneous mixtures (they are polydisperse).
What is Mn and how do we calculate it
The number average molecular weight - describe the average size of polymer chains in a sample, especially when those chains have different lengths.
