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What do lipases do?
They catalyse the hydrolysis of triglycerides
Are inorganic catalysts homogeneous or heterogeneous?
How do you calculate 1st order kinetics?
How can you rewrite 1st order kinetics equotation if A0 is constant?
lnAt =-k1t + C
How do you calculate the half-life in 1st order reactions?
What is a pseudo first order reaction?
e.g. a 2nd order reaction with water, so that (B) can be seen as constant and kinetics are more that of a first order reaction
How do you calculate the rate constant in pseudo 1st order reactions?
k2(CH3I)(H2O)= k1'(CH3I) where k1' = k2(H2O)
What is true for reversible reactions at equilibrium?
Bt is constant, so k1Ae = k-1Be = K-1xe
what is the steady state approach?
Assume (A.B) is constant
How do you calculate the rate constant for preequilibria?
Which possibilities are there for preequilibria?
- k2>>k1 and v=k1AB
- k1>>k2 and v= k2KAB
What is the Arrhenius equotation?
kobs= A exp(- Ea/RT)
How can you determine Ea?
- Measure at 2 different temperatures
- k1/k2 = exp (-Ea/R (1/T1-1/T2))
How do you calculate the reaction rate if (A0) = (B0)?
1/At - 1/A0 = k2 t
What does x stand for in rate constant calculations?
The concentration of product
What is K?
The equilibrium constant k1/k-1
You can also calculate it by xe/ (A0-xe)
What is K** and how do you calculate it?
It is the rate constant for formation of the transition state and is calculated by X**/(AB)
What is k**?
The reaction rate between transition state and product
What is kB?
The Boltzmann constant
What is h?
What is true concerning G in equilibria?
Which are the Eyring equotations?
- k= (kBT/h) exp (-G**/RT)
- k= (kBT/h) exp (-H**/RT) exp (S**/R)
What is the procedure to obtain activation parameters?
- 1. determine k at different T
- 2. plot ln(k/T) against 1/T
- 3. the slope is -H**/R
- 4. use Eyring to obtain S**
- 5. obtain G** from G=H-TS
What does the value for S** tell you?
- if S = 0 J/molK, then the reaction is monomolecular
- if S < 0 J/molK, then the reaction is bimolecular
What is more solvated: ions in ground state or in transition state?
In general, ions in ground state are more solvated
What effect does solvation have on EA?
It makes it bigger
What is the Hammond Postulate?
The transition state closely resembles the species with the highest energy content
What is the primary isotope effect?
Differences in bond strength depend on size of the molecule and affect reactivity
How can you calculate the maximum primary isotope effect?
The difference in k for the two different isotopes is the primary isotope effect
What does the primary isotope effect tell you?
- if kH/kD = 4-7, then bond cleavage and symmetrical transition state
- if kH/kD = 1-4, then bond cleavage, asymmetrical transition state
Which types of proton transfer are there?
- Fast, to N,O,S
- Slow, to C
- Diffusion dependent, from H3O+ to N or O
What are criteria for a nucleophilic catalyst?
- The catalyst has to react faster than the nucleophile (good nucleophile)
- The intermediate has to react faster with the nucleophile than the starting material (good leaving group)
How can you calculate the nucleophilic power?
- With the Edwards equotation
- log (k/k0) = alpha P + beta H
- where k0 is the rate constant with standard nucleophile
- P is polarisability
- H is basicity (= pKa + 1.74)
What are limits of the Edwards equotation?
- Does not take solvent into account
- does not take the alpha effect into account
What is the alpha effect?
If a nucleophile has a free electron pair on the atom immediately next to the nucleophile atom, it is much more reactive.
What are properties of hard nucleophiles?
hardly polarisable, strong base
What are properties of hard electrophiles?
What is the Bronsted plot?
- There is a linear correlation between log k and pKA in general base catalysis