Chapter 5 Flashcards
Describe the characteristic reaction of Alkenes
Nucleophile (alkene/base/negative) + Electrophile (acid/positive)
in each reaction, the pi bond of the alkene has been broken, and sigma bonds are formed to new atoms or groups on each carbon of the former pi bond
An _________ is a graph of energy changes that occur during a chemical reaction. Energy is plotted on the _____ axis and reaction progress on the ____ axis
Energy Diagram
Y
X
Draw an energy diagram for a one-step, exothermic reaction in which C reacts with A-B
In an energy diagram, the number of steps = __________
number of transition states
______________ is an unstable species of __________ energy, on an energy diagram, formed during the course of a reaction.
Transition state
maximum
Describe activation energy, what does Ea determine?
Activation energy is the difference in energy between the reactants and the transition state. Ea determines the RATE of the reaction.
If Ea is large . . .
Very few molecular collisions occur with sufficient energy to reach the transition state, the reaction is slow
If Ea is small . . .
Many molecular collisions occur and generate sufficient energy to reach the transition state, the reaction is fast
ΔH represents what?
Heat of reaction, the difference in energy between reactants and products, NOT transition states
When the energy of the products is lower than the reactants, heat is liberated and the rxn is ________
exothermic
When the energy of the products is higher than the reactants, heat is absorbed and the rxn is ___________
endothermic
What is the reaction intermediate?
An energy minimum between two transition steps. Intermediates are highly reactive and rarely can be isolated
What is the rate determining step?
The step in a reaction sequence that crosses the HIGHEST energy barrier and is thus the SLOWEST step in a multistep reaction
What is a reaction mechanism? What does it describe?
A rxn mechanism is a step-by-step description of how a reaction occurs and describes:
- which bonds break/ new bonds form
- order and relative rates of various bond breaking/forming
- solution? solvent role?
- catalyst role (if present)
- the energy of the entire system
A reaction mechanism is NOT . . . ?
a list of reagents or experimental conditions that bring about the chemical transformation
A rxn mechanism uses the symbolism of a __________ to show the redistribution of valence e- that occurs as . . .
curved arrow
covalent bonds are broken and new ones form
Why are reaction mechanisms used in chemistry?
Pattern 1 that is common in reaction mechanisms is the addition of a __________. A ___________ is used to show the redistribution of valence e- and formation of new covalent bonds.
Proton
curved arrow
Draw the Pattern 1 reaction between acetic acid (CH3COOH) and ammonia
A proton can be added across a C=C pi bond to form a new ______________. Adding a proton is typical of all reactions that . . .
C-H bond
are catalyzed by an acid
Pattern 2 involved the _________ of a proton. It is similar to pattern 1 except the focus is placed on . . .
removal
the compound that loses the proton INSTEAD of the compound that adds a proton
Draw the Pattern 2 reaction that would create acetic acid (CH3COOH) and ammonia
Pattern 3 involves the reaction of an electrophile and nucleophile to form a ____________________
New covalent bond
Define electrophile and nucleophile. Draw the reaction between CH3 and a chloride ion.
Pattern 4 involves the rearrangement of a bond when . . .
the e- of a sigma bond break the bond from one atom and form a new covalent bond to an adjacent atom
Pattern 5 is when a bond is broken to form a stable molecule. For example, a carbocation can be formed when . . .
Using the molecule CH3-CH=CH2, draw the electrophilic addition of a hydrogen halide
Using the molecule CH3-CH=CH2, draw the electrophilic addition of water/hydration
Using the molecule CH3-CH=CH2, draw the electrophilic addition of halogens/halogenation
When HCl is reacted with 2-butene, a two-step mechanism occurs. What are the two steps?
Describe the structure of a tert-butyl carbocation.
- bond angles about the (+) C are ~120
- C’s use sp2 hybrid orbitals to form a sigma bond to each attached group
- the unhybridized 2p orbital lies perpendicular to the sigma bond framework and contains NO e-
What are carbocations?
A species containing a carbon atom that has 3 bonds to it, 6 e- in the valence shell, and bears a (+) charge
Carbocations are ____________ that is, they are e- loving. Carbocations are also _________ that is, they are e- pair acceptors
Electrophiles
Lewis Acids
Describe the pattern of stability for carbocations based on carbon classification
How does the inductive effect impact the stability of a carbocation?
_______ carbocations are more stable and require a lower activation energy for their formation than _____ carbocations. _______ and ______ carbocations are so difficult to form that they are NEVER observed in solution
3
2
1
