Learning Objectives
Learning ObjectivesTo understand the mechanism of ELECTROPHILIC
ADDITION in alkenesTo understand how to precisely draw organic
reaction mechanismsTo apply your knowledge of electrophilic
addition to make predictions using more complex molecules Higher
Challenge
Success CriteriaYou can draw the mechanism of electrophilic
addition showing clearly where curly arrows begin and endYou can
explain what is happening at each point in the mechanismYou can
apply the mechanism to more complex moleculesYou can look for
patterns in information , spot the detail and apply it in different
situations
What is a mechanism in organic chemistry?A stage by stage
account of the transfer of electrons resulting in bond formation at
various stages in a reaction.
Organic chemistry mechanisms are about + attacking then sharing
electron pairs forming new covalent bonds
ELECTROPHILES are electron deficient species which seek out
centres of NEGATIVE CHARGE. They are ELECTON PAIR
ACCEPTORS.NUCLEOPHILES are ELECTRON RICH SPECIES which seek out
centres of positive charge. They are ELECTRON PAIR DONORS.
Electrophilic attack on a molecule?
Electrophilic attack on a molecule?The electrophile will seek
out a centre of NEGATIVE CHARGE take an ELECTRON PAIR and so end up
covalently bonded to the molecule
Electrophilic attack on a molecule?The electrophile will seek
out a centre of NEGATIVE CHARGE take an ELECTRON PAIR and so end up
covalently bonded to the molecule
Nucleophilic attack on a molecule?
Nucleophilic attack on a molecule?The nucleophile will seek out
centres of positive charge give them an electron pair and end up
covalently bonded to the molecule.
Nucleophilic attack on a molecule?The nucleophile will seek out
centres of positive charge give them an electron pair and end up
covalently bonded to the molecule.
Ethene + Bromine 1,2-dibromoethaneC2H4 + Br2 CH2BrCH2Br
This is the EQUATION for the reaction but what is the
MECHANISM?Think back to GCSE what is this reaction used for?
Ethene + Bromine 1,2-dibromoethaneC2H4 + Br2 CH2BrCH2Br
This is the EQUATION for the reaction but what is the
MECHANISM?Think back to GCSE what is this reaction used for?RED
Colourless
TaskA back to the boardB facing boardB tells A what to draw..The
mechanism of ELECTROPHILIC ADDITION TO ALKENES be RUTHLESS in your
quest for accuracy!
Electrophilic Addition Reaction of Bromine with
EtheneElectrophilic because initial attack is by an electron
deficient molecule on the electron rich double bond
Addition because a small molecule adds across the double bond to
form one new molecule
Curly arrows represent movement of a PAIR of electronsArrows
start at either a LONE PAIR or the MIDDLE of a BONDArrows end
either between atoms, where a new covalent bond forms, or as a lone
pair on an atom so on the atom
Going into the pit meansyou are
learning!HappyNervousExcitedChallenged! Ready to prove you can do
it!Empowered, you know the answer!Angry!Frustrated!On the verge of
giving up!
Doubt!Fear!Confusion!Inspiration!
17
You are going to have to decide WHICH END OF THE MOLECULE WILL
ACT AS THE ELECTROPHILE
ELECTROPHILES are electron deficient species which seek out
centres of NEGATIVE CHARGE. They are ELECTON PAIR
ACCEPTORS.NUCLEOPHILES are ELECTRON RICH SPECIES which seek out
centres of positive charge. They are ELECTRON PAIR DONORS.
Which of these is true?A. Electrophiles are electron rich
speciesB. Carbocations carry a full negative chargeC. Nucleophiles
are attracted to negative chargesD. Nucleophiles are electron pair
donors
Which of these is false?In the electrophilic addition of Br2 to
etheneThe electron density of the double bond has a polarising
effect on the bromineThe slightly positive end of bromine behaves
as a nucleophileC. The :Br ion behaves as an electrophileD. A pair
of electrons on the bromide ion forms a covalent bond with the
carbocation
null3996.742