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!

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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

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