More on Alkenes Flashcards
What happens in an electrophilic reaction?
In an ELECTROPHILIC ADDITION reaction, the alkene double bond opens up and the atoms are ADDED to the carbon atoms.
Why does the electrophilic addition reactions happen?
Electrophilic addition reaction happens because the double bond has got plenty of ELECTRONS and is easily attacked by ELECTROPHILES.
Why are electrophiles attracted to double bonds?
Electrophiles are electron-pair acceptors - they’re usually a bit short of electrons, so they’re attracted to areas where there are a lot of electrons about.
Electrophiles include …
positively charged ions, like H+ and NO2+, and polar molecules (Since the positively charged atom is attracted to places with lots of electrons)
Adding Hydrogen to C=C bonds include …
Alkanes.
Ethene will react with Hydrogen gas in an addition reaction to …
produce ethane.
It needs a nickel catalyst and a temperature of 150 degrees.
How is margarine made?
Margerine is made by ‘hydrogenating’ unsaturated vegetable oils. By removing some double bonds, you raise the melting point of the oil so that it becomes SOLID at room temeperature.
Halogens react with Alkenes to form…
Dihalogenoalkanes.
Halogens will react with alkenes to form DIHALOGENOALKANES - …
the halogens add across the double bond, and each of the carbon atoms ends up bonded to the halogen atom. It’s an ELECTROPHILIC ADDITION REACTION.
When you shake an alkene with brown bromine water, the soolution quickly decoulourises. Why?
This is because bromine is added across the double bond to form a colourless DIBROMOALKANE.
So BROMINE WATER is used to test for the presence of carbon-carbon double bonds.
Alcohols can be made by…
Steam hydration
Alkenes can be hydrated by…
STEAM at 300 degrees and a pressure of 60-70atm. The reaction needs a solid PHOSPHORIC (V) ACID CATALYST.
If you shake an alkene with ACIDIFIED POTASSIUM MANGANATE(VII) at room temperature, the…
purple solution is DECOLOURISED. You’ve OXIDISED the alkene and made a diol (an alcohol with two OH) groups.
Alkenes also undergo ADDITION reactions with hydrogen halides - to form …
Halogenoalkanes
Carbocations with more ALKYL GROUPS are more stable because …
the alkyl groups feed ELECTRONS TOWARDS THE POSITIVE CHARGE.
The MORE STABLE CARBOCATION is more likely to form.
Keywards: UNSYMMETRICAL alkene
Stable
Carbocation
What is the Markownkoff’s rule?
The MAJOR PRODUCT from addition of hydrogen halide (HX) to an unsymmetrical alkene is the one where HYDROGEN adds to the carbon with the MOST HYDROGEN already attached.
Alkenes will react with COLD CONCENTRATED SULFURIC ACID to form…
Alkyl hydrogen sulfates.
You can convert the alkyl hydrogen sulfates formed into ALCOHOLS by adding water and warming the reaction mixture.
But-1-ene is an alkene. Alkenes contain at least one c=c double bond.
a) Describe how bromine water can be used to test for C=C double bonds.
Shake the alkene with bromine water. The solution goes from orange to colourless if a double bond is present.
But-1-ene is an alkene. Alkenes contain at least one C=C double bond.
a) Describe how bromine water can be used to test for C=C double bonds.
Shake the alkene with bromine water. The solution goes from orange to colourless if a double bond is present.
But-1-ene is an alkene. Alkenes contain at least one C=C double bond.
b) Name the reaction mechanism in the above test.
Electrophilic addition
Hydrogen bromide will react with but-1-ene by this meachanism ,producing two isometric products
Explain why is this the major product for this reaction.
The carbo cation with the most attached alkyl groups is the most stable intermediate and is the most likely to form.
