Orgo 2 Exam Questions
B) Inversion
Both acidic and basic ring opening of epoxides lead to an __________ of configuration. A) Retention B) Inversion
B) 8
Cyclic alkynes can exist only in ring sizes of ____ carbons or more. A) 4 B) 8 C) 7 D) 6
Cis, trans has too much sterics for reaction to occur, needs energy to rotate.
Does the dienophile need to be S-Cis or S-Trans?
1) 4n+2 violation 2) it's not flat (draw boat to illustrate)
Explain why 8 membered alkene ring is not aromatic?
Highly steric because of SP2 shape. Draw trans and cis versions as well as Trans <--------- Cis, Trans --> Cis showing that the Trans version is substantially more favorable that Cis.
Following bromination would not produce (E) -1,4-dibromo-2-butene but not (Z) -1,4-dibromo-2-butene. In order for (Z) -1,4-dibromo-2-butene to form, what intermediate has to be forming? Explain mechanistically.
False, it uses an induced dipole mechanism to react.
Halogenation uses a carbocation intermediate. True or False
if there is exactly one single bond separating them.
How can you tell if a pi bond is conjugated or unconjugated?
Because a carbocation formation would not result in Anti Addition
How do you know that X2 addition doesn't form a carbocation intermediate?
False, it's an SN2 concerted reaction (No carbocation formed) whole reaction takes place in one step.
Hydroboration is an SN1 type reaction. True/False
racemic mixture (50/50), Half Retention, Half Inversion
If you start with a chiral molecule what will products look like if you have a SN1 Reaction?
inversion of configuration
If you start with a chiral molecule what will products look like if you have a SN2 Reaction?
A) Endo
In Diels Alder reactions, under kinetic conditions, the _______ product is favored? A) Endo B) Exo
size of leaving group (I>Br>Cl>F)
In SN1 reaction what factor increases the percentage of the inversion product?
D) CCl4
In X2 addition reactions, what's an example of a solvent that would not overpower the second halogen to be the nucleophile? A) H20 B) Methanol C) Ethanol D) CCl4
A) Diene
In a Diels Alder Reaction, which one acts as the nucleophile? A) Diene B) Dienophile
A) Endo because the secondary interactions between the dienophile and conjugated diene makes the Endo product more stable and favorable.
In a Diels Alder reaction, which product is more favored? Why? A) Endo B) Exo
H2SO4 deprotonates into H+ and HSO4, where the H is then picked up by H2O in solution to create H3O- (Hydronium Ion).
In an acid-catalyzed hydration reaction, how does H2SO4 enhance the reaction?
B) Base
In epoxide ring opening, what condition would result in an SN2 type reaction? A) Acidic B) Base
A) SN1-like
In epoxy-ring opening does acidic behave like SN1 or SN2? A) SN1-like B) SN2-like
A) Endo, because there are Secondary Interactions
In the Diels Alder reaction, what transition state does this correspond to? How do you know? A) Endo B) Exo
B) Exo because there are no Secondary Interactions
In the Diels Alder reaction, what transition state does this correspond to? How do you know? A) Endo B) Exo
C) Hydrogen, 1 will attach on least sterically hindered.
In the compound LiAlH4, what will act as the nucleophile in the reaction? A) Lithium B) Aluminum C) Hydrogen
A) Phenyl
In the compound PhMgBr, what will act as the nucleophile in the reaction? A) Phenyl B) Magnesium C) Bromine
Ring Strain
In this X2 addition reaction, the halogen added at the alkene and not the alkyne, what is the source for this regioselectivity?
A) Acidic
In this opening of an epoxide, under which condition is it occurring? A) Acidic B) Base
Anit-aromatic because it's conjugated, there's no sp3, it's cyclic and planar. This means it could still be aromatic, however it only has 4 pie electrons, which doesn't work for the (4n+2) rule; but it does work for the anti-cyclic rule of (4n) where n would = 1
Is this molecule aromatic, non-aromatic, or anti-aromatic? Why?
Aromatic, it's a complete ring (ruling out non-cyclic), it has only sp3, it's planar, and it follows the 4n+2 rule (ruling out anti-cyclic)
Is this molecule aromatic, non-aromatic, or anti-aromatic? Why?
Non-aromatic, this molecule follows every rule except for the first because it's not a complete ring.
Is this molecule aromatic, non-aromatic, or anti-aromatic? Why?
A) Conjugated
Is this molecule conjugated or unconjugated? A) Conjugated B) Unconjugated
A) Conjugated
Is this pi bond conjugated or unconjugated? A) Conjugated B) Unconjugated
B) Unconjugated
Is this pi bond conjugated or unconjugated? A) Conjugated B) Unconjugated
Hydration
Oxymercuration is a type of _____________ Reaction.
A) 3 pi bonds and the formation of 3 new bonds (2 sigma, one pi)
The Diels Alder reaction always involves the breakage of? A) 3 pi bonds and the formation of 3 new bonds (2 sigma, one pi) B) 2 pi bonds and the formation of 3 new bonds (2 sigma, one pi) C) 3 pi bonds and the formation of 4 new bonds (2 sigma, two pi) D) 1 pi bonds and the formation of 2 new bonds (1 sigma, one pi)
C - Catalyzing the rxn (creation of Hydronium Ion) P - Protonation of alkene (adding H to least substituted C) A - Addition of H20 to molecule at carbocation D - Deprotonation of H20 to OH + (regen of catalyst)
The acronym CPAD describes the four steps in a hydration reaction, what do the letters stand for?
A) True, it has two cumulated double bonds.
This is an allene. A) True B) False
B) False, this is a cumulenes, allenes only contain TWO double bonds
This is an allene. A) True B) False
B) False, this is a ketene. It's not a allene because one of the double bonds is attached to an oxygen
This is an allene. A) True B) False
1) Resonance 2) Being surrounded by electron donating groups (ie. Methyl)
Two ways a molecule can stabilize a carbocation.
Sterics
What controls the outcome of hydroboration?
Electrics
What controls the outcome of oxymercuration?
Sterics
What determines regioselectivity outcome in hydroboration and X2 Addition reactions?
Electrics
What determines regioselectivity outcome in oxymercuration reactions?
A) Substitution, Nucleophilic, Unimolecular
What does SN1 stand for? A) Substitution, Nucleophilic, Unimolecular B) Substitution, Nucleophilic, Monomolecular C) Substitution, Nucleophilic, Bimolecular
C) Substitution, Nucleophilic, Bimolecular
What does SN2 stand for? A) Substitution, Nucleophilic, Unimolecular B) Substitution, Nucleophilic, Monomolecular C) Substitution, Nucleophilic, Bimolecular
Acid Catalyst (H2SO4/H3O+)
What does a Hydration Reaction require?
Hydrogen
What does demercuration replace mercury with?
C) Hydride
What does the compound LiAlH4 known for generating? A) Water B) Halohydride C) Hydride D) Epoxide
Sterics
What factor plays a major role in determining the product regio-selectivity when BH3was employed?
Sterics
What factor plays a major role in determining the product regio-selectivity when Br2 was employed?
A hydrogen attached to a tertiary carbon (aka a hydride), undergoes rearrangement and switches places with the carbocation on the adjacent secondary carbocation. A hydride shift is not typically going to take place if they are not adjacent.
What happens during a hydride shift?
It changes to a carboxylic acid due to the removal of an oxygen that is now attached to the epoxide.
What happens to the peroxy acid functional group of an mCPBA molecule after an epoxide reaction?
To remove mercury from compound and replace it with hydrogen once oxymercuration reaction has taken place.
What is NaBH4 used for in oxymercuration reactions?
Induced Dipole
What is driving force behind the X2 Addition Reaction?
1) Better regioselectivity 2) Increases steric factor
What is the benefit of using Pinacolborane over BH3 for hydroboration reactions?
A) Endo
What is the configuration of this product? A) Endo B) Exo
B) Exo
What is the configuration of this product? A) Endo B) Exo
B) SP2
What is the hybridization of a carbon with a bond angle of 120 degrees A) SP B) SP2 C) SP3 D) SP4
B) SP2 exact
What is the hybridization of the transition state in SN1 reaction? A) SP2 like B) SP2 exact
A) SP2 like
What is the hybridization of the transition state in SN2 reaction? A) SP2 like B) SP2 exact
SP, 180 Degrees, Linear
What is the hybridization, bond angle, and shape of this element?
sp2, 120, trigonal planar
What is the hybridization, bond angle, and shape of this element?
sp3, 109.5, tetrahedral
What is the hybridization, bond angle, and shape of this element?
sp2 or trigonal bipyramidal
What is the intermediate shape for SN2 Reactions?
A six membered ring with an alkene.
What is the product of a Diels Alder reaction?
Formation of Carbocation
What is the rate limiting step of an SN1 reaction.
Markovnikov addition
What is the regiochemistry of an oxymercuration reaction?
mCPBA
What molecule is this?
B) 2pz
What orbital is responsible for forming a pie bond? A) 2p B) 2pz C) 2sp D) 2s
Strong nucleophilic solvents i.e. CH3OH, CH3O-, H2O
What solvents can affect the addition of the second halogen in the reaction?
Anti
What type of addition does halogenation use? Syn or Anti?
Syn Addition
What type of addition is used in Hydroboration Reactions?
C) Allenes
What type of intermediate is involved in this reaction? A) Carbocation B) Carboanion C) Allenes
A) SN1, it forms a carbocation intermediate
What type of reaction is Oxymercuration? A) SN1 B) SN2
Hydroboration
What type of reaction is this?
D) Epoxidation, uses peroxy acids
What type of reaction would this create? A) Hydrohalogenation B) Hydration C) Hydroboration D) Epoxidation
B) Anti-Markovnikov because hydrogen is more electronegative than boron, which puts hydrogen on the most substituted carbon.
What type of regioselectivity does hydroboration follow? Why? A) Markovnikov B) Anti-Markovnikov
Syn Addition
What type of stereochemistry does hydroboration follow? A) Syn Addition B) Anit Addition
There will be a bad electrostatic interaction between the because the proximal electronegative Cl or Br leads to electrostatic repulsion in the carbocation intermediate causing the rate of reaction to slow down significantly (Slide 32).
What would happen in this circumstance where the x is attached to the carbon that will help stabilize the carbon that will receive the carbocation?
The number of pie electrons, aromatic will follow 4n+2 so the number of pie e- will be 6,10,14... and anti-aromatic will follow 4n so 4,8,12... will be the number of pie e-
What's the only difference between anti-aromatic and aromatic?
B) Product Stability
When a reaction is under thermodynamic control the regioselectivity is determined by? A) Markovnikov B) Product Stability C) Height of peak at the transition state D) Acid Catalyst
B) SN1
When do electrics matter? A) SN2 B) SN1
A) SN2
When do sterics matter? A) SN2 B) SN1
Typically when a carbocation is formed on a secondary carbon and there is an adjacent carbon that is tertiary.
When does a hydride shift occur?
C) Height of peak at the transition state
When the reaction is under kinetic control the outcome is decided by? A) Markovnikov's rule B) Product Stability C) Height of peak at the transition state D) Acid Catalyst
A) Terminal
Which alkyne is the most acidic? A) Terminal B) Most conjugated C) Most substituted D) Central
A) SN1-like, forms a carbocation (in Moteki's class)
Which best describes oxymercuration? A) SN1-like B) SN2-like
Intermediate, because it's lower on the graph
Which is more stable transition state or intermediate? Why?
A) Toluene
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
B) Aniline
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
C) Phenol
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
D) Anisole
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
E) Benzaldehyde
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
F) Benzoic Acid
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
G) Benzyl Alcohol
Which molecule is this? A) Toluene B) Aniline C) Phenol D) Anisole E) Benzaldehyde F) Benzoic Acid G) Benzyl Alcohol
A
Which one of these is the Diene?
B
Which one of these is the Dienophile?
C) X2 Addition
Which one of these reactions is SN2? A) Hydrohalogenation B) Hydration Reaction C) X2 Addition D) All the Above
D (TERTIARY)
Which one would be the most stable carbocation A-D left to right?
C)Oxymercuration, because it forms carbocation it can undergo rearrangement.
Which reaction type could result in both 1,4 and 1,2 addition. A)Hydroboration B)Halogenation C)Oxymercuration D)Epoxidation
A) Meta
Which substitution pattern for disubstituted benzenes is this? A) Meta B) Para C) Ortho
B) Para
Which substitution pattern for disubstituted benzenes is this? A) Meta B) Para C) Ortho
C) Ortho
Which substitution pattern for disubstituted benzenes is this? A) Meta B) Para C) Ortho
A) SN1
Which type of reaction results in a racemic product? A) SN1 B) SN2
1) pz orbitals are aligned 2) electron density is shared
Why are conjugated dienes more stable? (2 reasons)
Because there is less resistance from steric inference in inversion
Why does inversion of configuration occur more often than retention in SN1 reactions.
a carbon (electronegativity 2.5) connected to hydrogen (electronegativity 2.2) will be electron rich, and can donate some of those electrons to the neighboring carbocation. In other words, the neighboring carbon pays the carbocation with electrons it steals from the hydrogens. Also, hyperconjugation, which invokes stabilization through donation of the electrons in C-H sigma bonds to the empty p orbital of the carbocation. Tertiary carbocations have more of these groups so it is more stable.
Why is a tertiary carbocation more stable than a primary carbocation?
1) SP Hybridized 2) %S = 50 3) Electrons are closer to nucleus 4) Anion Stabilized
Why is terminal alkene more acidic? (4 Reasons)
Because higher temperatures are under thermodynamic control which causes the more favored product to be the most stable product which is the 1,4 based on the graph.
Why would the 1,4-product be favored at higher temperature?
The nucleophile will attack on the less hindered side.
A reaction that is SN2 is controlled by sterics, when it comes to attacking what does that mean?
Ring Strain or Angle Strain (2 words only)
Alkoxy groups (OR) are considered as relatively poor leaving groups. In fact, simple ethers (R-O-R) are not generally cleaved in a strong base. Explain why do epoxides open relatively easily in basic conditions?
B) Unconjugated
Are these molecules conjugated or unconjugated? A) Conjugated B) Unconjugated
A) Thermodynamic Control
At higher temperature, most molecules have enough energy to overcome activation barrier and equilibrate to the more stable product; such reactions are said to be under? A) Thermodynamic Control B) Kinetic Control
B) Kinetic Control
At lower temperature, there are fewer molecules with the necessary energy to reach a higher transition state. Therefore, pathways with lower activation barrier are favored. The reaction is said to be under. A) Thermodynamic Control B) Kinetic Control
B) Dienophile
n a Diels Alder Reaction, which one acts as the electrophile? A) Diene B) Dienophile
A) Epoxides
mCPBA is association with which of the type of reaction? A) Epoxides B) Hydroboration C) X2 Addition D) H-X
