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ACS Organic Chemistry Exam
Covering the full series of Orgo I and II plus lab for the ACS standard exam
Terms in this set (71)
What is the general formula for a carbohydrate?
How do you determine the number of stereoisomers for a given carbohydrate?
2^n where n= number of stereocenters
Distinguish between the D and L designations for carbohydrates.
In the L form the hydroxy group is on the bottom left closest to the CH2OH group in the frame of a Fischer projection
In the D form the OH is on the bottom right
What are anomers?
Diastereomers formed by the cyclization of carbohydrates (*note they have different configurations at the new stereocenter-this is what makes them diastereomers)
Distinguish between alpha and beta anomers.
beta anomers have the OH belonging to the hemiacetal carbon equatorial
alpha anomers have the OH belonging to the hemiacetal carbon axial
What is the definition of mutarotation?
the process for which alpha and beta anomers come to equilibrium (aqueous) in a specific ratio. It is the same ratio is observed when you start with the alpha anomer in water versus the beta anomer in water
What agent is most often used for complete oxidation of a carbohydrate?
What kind of agents are used for selective or partial oxidation of carbohydrates?
most commonly Br or some other MILD oxidative agent
What are reducing sugars?
Carbohydrates that yield positive results of the oxidative tests, because in being oxidized they reduce the metal ion (or other reducing agent)
Carbohydrates undergo reactions similar to which functional group?
OH (hemiacetals and acetals)
How does the Tollen's test work?
Carbohydrate is oxidized by Ag+ and positive result shows a silvery mirror as Ag+ is reduced to metallic (elemental) silver
How do the Benedict's and Fehling's tests work?
Both employ a solution of aqueous Cu2+ in base. When reduced it forms Cu2O which is a red ppt.
What is a glycoside?
a sugar bonded to another oxygen containing functional group to make the carbohydrate a full acetal rather than a hemiacetal
What does a glycosidic bond consist of?
A glycosidic bond is between C4 (the acetal carbon) and another oxygen atom
What is the difference between an alpha and a beta glycosidic bond?
the alpha bond is axial
the equatorial bond is equatorial
What is a nucleophile?
An electron rich species than seeks an electron poor site
What is an electrophile?
An electron poor species which seeks an electron rich species
A nucleophile is, by definition what other classification of species?
What is the main difference, in terms of how the reaction occurs, between Sn1 and Sn2 reactions?
Sn1- the leaving group leaves then the nucleophile comes in
Sn2- the leaving group leaves as the nucleophile is coming in (simultaneously)
What stereochemistry do Sn2 reactions follow?
inversion of configuration (so from R to S or S to R) *Note inversion is the mirror image
What are the main differences between Sn1 and Sn2 reactions?
Sn2- more substituents hinder, will not happen for tertiary carbons, polar, protic solvents, inversion of configuration
Sn1- more substituents help, will not happen for primary carbons, forms carbocation, aprotic solvents, racemization (or else slightly more inversion of configuration than retention)
Do leaving groups affect the rates of Sn1 or Sn2 reactions?
What are general trends to determine the strength of a leaving group?
Going down a group on the periodic table increases the strength of the leaving group, if the leaving group is stable on its own, it is more likely to leave; strong bases make poor leaving groups
What are some of the trends for determining the strength of a nucleophile?
increasing base strength is proportional to the strength of the nucleophile, as you go down a column on the periodic table the nucleophile gets weaker, steric bulk decreases ability of nucleophile
Does the identity of the nucleophile have an effect on Sn1 or Sn2 reactions?
The identity of the nucleophile has no effect on the rate of Sn1 reactions because the nucleophile adds after the rate determining step.
What are the 3 most common aprotic solvents?
dimethylsulfoxide (DMSO), dimethylformamide (DMF), acetone
What are the 5 most common protic solvents?
water, ethanol, acetic acid, methanol, trifluoroacetic acid
When are Sn2 reactions favored?
aprotic solvents, strong nucleophile, primary substrates
When are Sn1 reactions favored?
stable carbocation (tertiary substates), poor nucleophiles, good leaving group, polar solvent
What is an elimination reaction?
When the leaving group and a proton on an adjacent carbon both leave to form a double bond
What is the term for the most basic type of eliminations?
1,2-eliminations (because proton and leaving group are on adjacent atoms); this can also be called beta-elimination
What, physically, happens in an E2 elimination?
Involves breaking and making several bonds all at once; the nucleophile will start to bond (taking the proton), the leaving group leaves and the double bond starts to form (remember all at once)
What do E2 eliminations typically compete with?
What is Zaitzev's Rule and in which kinds of reactions does it apply?
the product will be the more substituted compound; applies to elimination reactions-note, of course there are exceptions
What is the one "major" exception to Zaitzev's principle?
What does oxidation signify in organic chemistry?
results in an overall increase in the number of oxygens or a decrease in hyrdogen content
What does reduction signify in organic chemistry?
results in a decrease in oxygen content or an increase in hydrogen content
What happens when you oxidize a primary alcohol?
goes to an aldehyde and then straight to a carboxylic acid unless it is stopped
What happens when you oxidize a secondary alcohol?
What happens when you oxidize a tertiary alcohol?
nothing- it is inert
Distinguish between regiospecific and regioselective.
A regiospecific reaction is one wherein the reaction produces predominantly one possible orientation; regioselective means it forms some of both
What is Markovnikov's rule?
In reactions of HX to alkenes the H bonds to the carbon with more hydrogens (fewer substituents) and the X bonds to the carbon with more substituents (fewer hydrogens). This is for additions to alkenes/alkynes
What is the mechanism rule?
in additions to alkenes/alkynes the electrophile adds to form the most stable carbocation (more widely applicable-note this also accounts for rearrangement)
What is a halohydrin?
some species with both an OH group and a halogen bonded to 2 adjacent carbons
What is a carbene?
A carbon with only 2 bonds and an unshared pair- the simplest is CH2
What is Huckles rule?
4n+2 this tells us the number of electrons required for aromaticity
What are the requirements for aromaticity?
Is it flat? Cyclic? Conjugated? Huckle's number of electrons
What is the difference between anti-aromatic and non-aromatic (which is the same as neither aromatic nor antiaromatic)?
Anti-aromatic compounds do not have the correct number of electrons, but they do meet all of the other criteria
How do we deal with peripheral aromaticity?
rearrange the bonds such that they are all on the outside and there are no internal double bonds (on shared sides of a multi-ring system)
What is an arenium ion?
a benzene ring missing a hydrogen, giving one of the carbons a negative charge
What is an arene?
a ring structure with conjugated double bonds
What is a phenol?
an alcohol bonded directly to an aromatic ring
What are the numerical designations for meta, ortho and para?
ortho- 1, 2
What does the ending "-one" represent?
What is the ending (naming) for aldehydes?
What is an acyl chloride?
Distinguish between the following groups: amide, nitro and nitrile
nitrile- C triple bond N
What are the 3 main disadvantages of Friedel-Crafts alkylations?
1) the ending material is activated, meaning it is more reactive than the starting material (one of the few which adds activating group) and multiple substitution can be a problem
2) rings with moderate-strong deactivating groups cannot be alkylated
What is a diazo group?
What is an arylamine?
an aromatic ring (in our case nearly always benzene) with an NH2 group
What is a hydrate?
A carbon with 2 OH groups
What is a ylide?
What are imines?
really just aldehyde/ketone but instead of the O it is an N
What are imines reduced to?
What compound reduces imines?
When is an enamine formed?
reaction of a secondary amine with a ketone/aldehyde
How are imines formed?
reaction of a primary amine with an aldehyde/ketone
What is an enamine?
amino group bonded to one of the carbons of a C=C
What is an acetal?
a carbon which is bonded to 2 oxygens which are not OH
What is a hemiacetal?
a carbon bonded to 2 oxygens, one of which is an OH, the other is not
What does an amide hydrolize to?