Ch. 4 Flashcards
Where is the electron in a free radical?
The p orbital
Initiation
Make radicals from nonradicals
Propagation
Radical reacts with nonradical
Termination
Two radicals react to form nonradicals
Keq (products and reactants)
[products]. [C]c[D]d
= —————– = ————
[reactants]. [A]a[B]b
What is ∆G
the amount of energy available to do work; energy of products - energy of reactants
∆G formula
∆Gº = -RT(lnKeq); ∆Gº = ∆Hº - T∆Sº
Enthalpy
Change in bonding energy
Entropy
Change in disorder
Do cyclic molecules or acyclic molecules have more entropy?
Acyclic because cyclic molecules have restricted bond rotation
What does ∆E equal to
∆Gº
Bond dissociation ________ energy, bond formation ________ energy
requires, releases
Homolytic cleavage
When the bond breaks, each atom gets one electron
Heterolytic cleavage
When the bond breaks, the most electronegative gets both electrons
What range do most BDE fall between
60-100 kcal/mol
Rate law equation (for A+B –> C + D)
rate = kr[A]a[B]b
What is order
Order is the number of molecules of that reactant which is present in the rate-determining step of the mechanism
Rate constant formula
kr = Ae^(-Ea/RT)
What is activation energy
the minimum kinetic energy needed to react
What is the value of R (gas constant)
8.314 J/Kmol
Intermediates
Short-lived species on the way to a product
Transition states
the highest point in energy between two chemicals
Rate Determining Step
The slowest step in the reaction will have the highest energy transition state
With ____ Ea, rate decreases
increasing
With ______ temperature, rate increases
increasing
_______ reacts explosively
Fluorine
_____ must be heated to react
Bromine
_______ reacts at a moderate rate
Chlorine
_______ does not detectibly react
Iodine
Is a tertiary radical or primary radical more stable
tertiary
With increasing degree, dissociation energy gets ________
weaker
What does it mean that bromination is highly selective
Prefers tertiary over secondary over primary
In an endothermic reaction the transition state resembles the _____; in an exothermic reaction, the transition state resembles the _________.
product; reactant
Hammond Postulate
Transition state looks like what it is closest in energy to
Bromination is exo/endo thermic, Chlorination is exo/endo thermic
Bromination: endo
Chlorination: exo
Bromination has a _______ difference in Ea, Chlorination has a ______ difference in Ea
large, small
What degree carbocation is most stable
tertiary
What are the two ways carbocations are stabalized by alkyl substituents
Inductive effect, hyperconjugation
Inductive effect
Donation of electron density along the sigma bonds
Hyperconjugation
Overlap of sigma bonding orbitals with empty p orbitals
Carbanions
Eight electrons: six bonding, one lone pair
Negative charge
Nucleophilic and basic
What degree is most stable for carboanions
Methyl, then primary
Carbenes
Have a neutral carbon
Vacant p orbital, so it can react as an electrophile
Has a lone pair in the sp2 orbital so it can react as a nucleophile
