Reaction Mechanisms - Addition of Alkenes + Equilibrium
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What is the most common reaction of alkanes?
Substitution
What is the general formula for the substitution for alkanes?
R-H + A-B = R-A + H-B
R-H + A-B = R-A + H-B What is H substituted with?
H is substituted with A
R-H + A-B = R-A + H-B What is B in this?
The LG -> limiting?
What is the most common reaction of alkenes?
Addition
What is the general formula for the addition of alkenes?
C=C + A-B = C-C(A-B -> drawn bellow in molecular formula))
What three things can be added to alkenes by a two step polar process?
Addition of halogens Addition of water (hydration) Addition of acids
What happens in the addition of halogens? 3
Cl2 and Br2 can be added readily Happens nearly instantaneously even at room temperature or below No light or heat is required
Name two halogens that can be readily added to alkenes?
Cl2 Br2
What is not needed for the addition of halogens? 2
Light Heat
Heat is not needed for the addition of halogens, what is this similar to?
Similar to the substitution of alkanes
What happens in the addition of water? 2
An acid catalyst is required because a neutral H2O molecule is not acidic enough to provide protons to start the reaction Its a multistep mechanism
What is needed in the addition of water?
An acid catalyst
Why is an acid catalyst needed in the addition of water?
Because a neutral H2O molecule is not acidic enough to provide protons to start the reaction
What is needed to start the reaction of hydration?
Protons
What happens in the addition of acids? 3
This applies a variety of acids The first step involves the addition of a H+ to the C=C bond X- is then added (acid with negative charge)
How many products can be formed using a symmetric reagent and/or alkene?
One one addition product is possible
How many products can be formed using an unsymmetrical reagent/and or alkene?
Two products are possible
What are regioisomers?
Isomers which have the same functional groups but attached at different positions
What is it called if an addition reaction involving both an unsymmetric alkene and reagent MAINLY only gives one regioisomer?
The reaction is said to be regioselective
Most reagents used in addition reactions are polar, what does this mean?
There is a + and a - end e.g. H+Cl-
What is the Markovnikov rule? 2
When an unsymmetrical reagent adds to an unsymmetrical alkene The electropositive part of the reagent bonds to the C of the C=C that has the greater number of H atoms attached to it
What does the Markovnikov rule apply to?
When an unsymmetrical reagent adds to an unsymmetrical alkene
What are electrophiles? 4
Electron lovers They are electron poor reagents They seek electrons They are often + ions (cations) or otherwise electron deficient species