Organic Reactions
Kinds of Reactions
Mechanisms (polar, non-polar)
Bond Dissociation Energy
Reaction Profiles
Types of Reactions
• Addition Reactions
H
H
H
C=C
H
+ HBr
C
H
H
Br
C
H
H
H
• Elimination Reactions
H
Br
C
H
H
C
H + NaOH
H
H
H
C=C
H
+ H2O
H + NaBr
Types of Reactions
• Substitution:
– Polar
H
H
H
H
+ KCN
NC
Br
H
H
– Non-polar
CH4 + Cl2
light (h)
CH3Cl + HCl
+ KBr
Rearrangement
Definitions
• Mechanism: Complete step-by-step of exactly
which bonds break and which bonds form and in
what order.
• Thermodynamics: The study of the energy
changes that occur in chemical transformations.
This allows for comparison of stability of
reactants and products.
• Kinetics: The study of reaction rates, determining
which products are formed most rapidly. One can
predict how the rate will change with changing
conditions.
Reaction Profile (Exothermic)
a
b
rate = k r[A] [B]
nd
2
CH3Br + OH
Order Reaction
CH3OH + Br
Rate = k[CH3Br][OH ]
se con d orde r rate k in e tics
st
1
Order Reaction
(CH3)3CBr + H2O
(CH3)3OH + HBr
Rate = k[(CH3)3CBr]
First orde r rate k in e tics
Bond Breaking:
Non-polar and Polar
Bond Forming:
Non-polar and Polar
Non-polar Reaction Involves
Free Radicals
Free Radicals are Neutral, but
Electron-Deficient
Free Radical Chlorination
Experimental Evidence Helps
to Determine Mechanism
• Chlorination does not occur at room
temperature in the dark.
• The most effective wavelength of light is
blue that is strongly absorbed by Cl2 gas.
• The light-initiated reaction has a high
quantum yield (many molecules of product
are formed from each photon of light).
Initiation
Free Radical Species are Constantly
Generated Throughout the Reaction
Propagation
Termination: Reaction of any 2 Radicals
Chlorination of Propane
40%
60%
Chlorination of Methylpropane
.
CH3
CH3
C
H + Cl .
CH3
CH3
CH3
CH2Cl
H
+ Cl2
CH3
C
CH3
CH3
CH3
CH3
C.
CH3
C.
CH3
CH3
CH2
C
H + CH3
C
.
CH3
CH3
CH2
+ Cl2
CH3
C
CH3
H 65% + Cl.
Cl 35% + Cl .
3o Radicals are Easiest to Form
Stability of Free Radicals
Consider the free radical monochlorination of
2,2,5-trimethylhexane. Draw all of the
unique products (ignore stereoisomers; use
zig-zag structures please).
Polar Reactions:
Nucleophiles & Electrophiles
Nucleophiles are Bases
Electrophiles are Acids
Reactions Often Go Through
Intermediates
Transition State
Addition Reaction is a TwoStep Mechanism
How Many Mechanistic Steps?
How Many Intermediates?
How Many Transition States?
Which Step is Rate-Determining?