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25 Cards in this Set
- Front
- Back
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Define Ethers and the properties associated with ethers
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Ethers are compounds with the formula R-O-R’ where both R’s can be alkyl groups or aryl groups. Ethers with the exception of Epoxides are relatively unreactive and are used for solvents. Ether contain an Sp3 hybridized oxygen atom with bond angles with that close to a tetrahedral but closer to 110 bond angle due to bulky groups. Oxygen atom in Ethers are polar.
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Ether boiling point characteristics
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the alcohols are hydrogen bonded giving them much higher boiling points. the ethers have boiling points that are closer to those of alkanes with similar molecular weights
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ethers form complexes with nucleophiles or electrophiles and why
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electrophiles. Ether’s non bonding electrons also stabilize borane, BH3. Pure borane exists as a dimer which is a dangerous solvent so THF forms a complex with BH3 to help stabilizes boron
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Crown ether complexes
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larger cyclic polyethers that specifically solvate metal cations by complexes the metal in the center of the ring
12- Crown-4 solvates Li 15- crown-5 solvates Na 18-Crown-6 solvates K+ |
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heterocyclic compunds/ heteroatom
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contains a ring in which a ring atom is an element other than Carbon this atom is called heteroatom
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what are epoxides
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three membered cyclc ethers
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Oxetanes
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least common cyclic ethers four membered rings
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Furans (oxylanes)
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five membered cyclic ether are commonly named after an aromatic member of this group furan
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pyrans (oxanes)
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the six membered cyclic ethers are commonly named as derivatives of pyran
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dioxanes
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heterocyclic ethers with two oxygen atoms in a membered ring `
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Explain the mechanism of the Williamson Ether sythesis
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...
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What are the other two methods of sythesis of ether besides the williamson ether
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addition across the double bond alkoxymercuration-demercuration
and bimolecular dehydration of alcohols |
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Explain the mechanism behind the cleavage of ethers
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1- protonation of the ether to form a good leaving group2
2- Sn2 cleavage of the protonated ether 3-conversion of the alcohol to alkyl halide 4-protonated ether undergoes Sn1 and Sn2 by bromide ion |
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In order for an electrophilic substitution with Benzene what must happen first
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Ferric bromide and other lewis acidsenhance the electrophilic strenth of bromine by forming a complex anion
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What are the reagents and co reagents for nitration of Benzene to occur
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the first is the reagent H2SO4 and the co reagent is HNO3 to form a nitronium ion
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What is the electophile for a nitration reaction and how do you get it
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HNO3 with H2SO4 catalyst
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Name the two methods for the nomenclature of cyclic ethers
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the first method would be the name the rest of the molecule and use the term epoxy as a substituent giving the numbers of the carbons atoms bounded to the epoxide atom
Second method- is to name epoxides as derivatives of the parent compound, using oxirane as the systematic name in this method the heterocyclic compound are numbered starting with the heteroatom and going in the direction to give the lowest substituent numbers |
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when talking about the williamson ether synthesis what are the three main concerns
Hint: alcohol reactivity, intermediate, alkyl halides |
1. alcohol reactivity follows methyl>1>2>3
2. deprotantion of hydroxide group with an active metal K, NA or NaH (THF) to form alkoxide on the most hindered R group |
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Ethers react with excess HBr in acidic conditions what are the 4 steps
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step 1: protonation of the H-Br by the Oxygen on ether
step 2: bromination attack displaces R' leaving an alcohol step 3 protonation by alcohol to leave an watter attached step 4: wter leaves bromine attacks carbocations |
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what is one way to form symmetric ethers
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dehydration of an alcohol by acid at 140 degrees if temp is higher elimination will take place
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when using strong acids like HBr and HI usually forms an alkyl halide for all reactiings what is the only exception to that rule
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A benzyl alkyl group will form phenol prodyct because it will not attack a 2 degree carbon that will not be an sn2
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What makes epoxides good reactants
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epoxide is very strained and vulnerable to even bases
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what are the two reactions that take place with epoxides and what are the major products
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1. reactions with acid in presence of water H+/H2O will yield a diol as the major product
2. reaction of acid in the presence of an alcohol H+/CH3CH2OH will yield an alcohol and an ether |
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what are the requirements for aromaticity
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1. has to be cyclic
2. each member of the ring has to be Sp2 hybridized 3. each member must have conjugated p orbitals. conjugated double bonds in a molecule, mean that the single and double bonds alternate 4. these pi orbitals are occupied by 4n+2 electrons this is the huckel rule |
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benzene takes place in electrophillic substitutions what are the reagents and co reagents for all of them
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1. br2/ FeBr3 / Cl2/ FeCl3
2. Nitration co reagents are NO3/H2SO4 substituents NO2 3. Sulfonation- SO3/H2SO4 substituents SO3H 4. alkylation friedel crafts -R-Cl & heat / AlCl3 catalyst 5. electrophile CH3C(=O)Cl with AlCl3- substituent CH3C=O 6. oxidation-(1) KMnO4, OH- (2) H3O+ substituent COOH |
