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31 Cards in this Set
- Front
- Back
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What are the 2 types of addition of halogens to alkenes
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ionic addition
radical addition what are the products |
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What are the types of addition to alkenes
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Hydration
Hydrogenation Hydroxylation Oxidative cleavage Epoxidation Halogenation Halohydrin formation HX addition cyclopropanation |
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draw steps for ionic addition of HBR to propene
what is regiochem? |
done on paper
H+ abstracted from HBr carbocation formed on more substituted carbon. Br- adds to carbocation. Markovnikov orientation |
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draw steps for radical addition of HBR to propene
Does this work with all halogens? What is regiochem? |
done on paper
Br rad formed. Br rad adds to less substituted carbon and alkyl rad forms on more substitued carbon. Alkyl radical abstracts hydrogen from HBr regenerating Bromine rad. This does not work with all halogens, only Bromine. Anti Markovnikov orientation |
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If you want to add Bromine to the antimarkovnikov position what would you use
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HBr and peroxide in a greater amount. The peroxide forms radicals which generate Bromine radicals.
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If you want to add a halogen in the markovnikov position what do you do
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Add HX to a polar aprotic solvent like ether.
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describe acid catalyzed hydration of an alkene.
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double bond gets proton from H3O+ and carbocation formed on more substituted carbon. Water is added to the carbocation. A proton leaves on a water leaving the OH on the more substituted (Mark. position)
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describe oxymercuration of an alkene.
What is the regiochemistry. |
Electrophilic attack of +Hg(OAc) makes a 3 membered ring where the double bond was. Addition of water to the more substituted carbon opens the ring. NaBH4 is added and removes the +Hg(OAc)and replaces it with a proton.
Markovnikov addition. |
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What is the benefit of oxymercuration.
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It gives better yield of the Markovnikov orientation over the acid catalyzed addition because it does not allow the opportunity to rearrange.
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describe alkoxymercuration.
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Similar to Oxymercuration only taking place in an alcohol.
+Hg(OAc)makes a ring where the double bond was. Alcohol opens the ring on the more substituted carbon. The alcohol loses the proton becoming an ether and NaBH4 gives removes the mercury and donates a hydride fully saturating it. |
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Describe hydroboration of alkenes.
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Either B2H6 or BH3-THF is added to an alkene. The Boron containing molecule adds a Hydrogen to the more substituted carbon, the boron goes to the other. Peroxide and hydroxide is added and the hydroxide replaces the Boron on the same side for syn addition anti markovnikov orientation.
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Describe formation of halohydrins
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X2 loses one X to form a ring where the double bond was, the other leaves as X-. Water adds to the more substituted carbon. Water abstracts the extra proton leaving a hydroxyl.
Markovnikov orientation anti stereochem. |
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what is the regio and stereochemistry of halohydrins
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markovnikov orientation
anti stereochem |
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describe catalytic hydrogenation of an alkene
What solvent should it be in? What is the stereochemistry? |
solvent is an alcohol, an alkane, or acetic acid, platinum, palladium, or nickel is used as a catalyst. Hydrogen is adsorbed onto the metal where the metal weakens the bonds. Hydrogen is added in syn addition.
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What is Wilkinson's Catalyst?
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A big bulky thing with Rh at the center and lots of PPh groups. It is used to hydrogenate alkenes and can have replacement groups to create selective chiral molecules.
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What is Ru (BINAP) Cl2
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another big bulky catalyst to produce chiral molecules from achiral molecules.
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What is asymmetrical induction?
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Producing chiral molecules from achiral molecules with enantionmeric excess.
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What is the Simmons-Smith rxn
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ICH2ZnI is added to a carbene and it produces a cyclopropane and ZnI2 leaves.
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What is ICH2ZnI
What kind of reaction is it used for |
Iodomethyl zinciodate. It is called a carbenoid because it acts like a carbene.
It adds across a double bond to produce a cyclopropane. |
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Describe the formation of carbenes by alpha elimination.
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A halogenated carbon like CHBr3 is treated with a base and the hydrogen is abstracted then one X leaves with 2 electrons and you are left with CX2.
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What is an epoxide
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A 3 membered cyclic ether.
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What is a peroxyacid
what is it used for what is the best one for us to use for this reaction |
a carboxylic acid where there is an extra oxygen attached to the oxygen before the acidic Hydrogen. C(O)-O-O-H
They are used to form epoxides We use MCPBA |
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How do you create an epoxide?
What stereochemistry is involved |
Add a peroxyacid, preferably MCPBA, to an alkene. It produces a 5 membered ring transition state and functions in 1 step.
There is a retention of stereochemistry. |
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Describe acid catalyzation of epoxides.
Draw this on a 5 membered ring |
H+ added to the oxygen. Water does a backside attack and opens the ring adding in the anti confirmation. Water abstracts a proton and leaves a diol in the anti conformation.
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How do you create a diol in anti conformation
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make an epoxide and open it by acid catalyzation.
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How do you create a syn diol
and which gives the best yield |
alkene and
OsO4 and H2O2 or KMnO4 cold and dilute OsO4 gives the best yield but is expensive and toxic |
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Describe syn diol formation from an alkene
What can reagents can be used |
Add something with 4 double bonded Oxygens hanging off. Then add something to replace that with OH groups.
OsO4 then H2O2, or KMnO4 then OH- and H2O. The mechanism is that it forms a 5 membered ring of some sort. |
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If you add hot concentrated KMnO4 to an alkene what is produced
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A mixture of ketones and carboxylic acids
Primary carbons become carboxylic acids and secondary carbons become ketones |
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If you have a terminal =CH2 and you add hot concentrated KMnO4 what is produced
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CO2 and water
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Describe ozonolysis of an alkene. What do you add after the ozone?
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It is the oxidative cleavage of an alkene by ozone then the reduction by (CH3)2S (dimethyl sulfide). It produces a ketone on a secondary carbon and an aldehyde on a primary.
A terminal =CH2 becomes H2C=O |
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What is NBS
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It is a good way to add Bromine for radical addition. I is a 5 membered ring with a N at the top connected to a Bromine. The carbons on the other side have a double bonded Oxygen attached.
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