CHM 235/238 Final Exam
exergonic
-an equilibrium will eventually be reached -A spontaneous process means there will be more products than reactants -The greater the magnitude of a (-)ΔG, the greater the equilibrium conc. of products
c. achiral, racemic
Acid-catalyzed hydration mechanisms proceed through a carbocation intermediate, which is __________. Therefore the products of these reaction are ____________.
c. low, small, high, large
Addition reactions are favored at ________ temperature when the entropy term in the Gibb's free energy equation will be ________. Elimination reactions are favored at ________ temperature when the entropy term in the Gibb's free energy equation will be ________ .
Due to symmetry, 3 only has 2 signals and both are singlets as neither has heterotropic neighbors
An unknown compound produces a HNMR spectrum that has just 2 signals, each of which is a singlet. Which of the compounds 1-4, could the unknown be? Explain.
a. diastereomers, configurational b. constitutional isomers c. identical d. diastereomers, configurational
Are the following pairs identical, enantiomers, diastereomers, or constitutional isomers. Also, which of these are configurational isomers of each other?
C. nucleophile attacks at the same time LG leaves *a is SN1, and b is impossible
Assuming the reaction below takes place by a concerted process, which mechanistic scheme is correct?
empty p-orbital=>electrophilic
Classify each of the highlighted regions below as either a nucleophilic center or an electrophilic center
inductive effect=>electrophilic
Classify each of the highlighted regions below as either a nucleophilic center or an electrophilic center
inductive effect=>nucleophilic
Classify each of the highlighted regions below as either a nucleophilic center or an electrophilic center
lone pair=>nucleophilic
Classify each of the highlighted regions below as either a nucleophilic center or an electrophilic center
π bond=>nucleophilic
Classify each of the highlighted regions below as either a nucleophilic center or an electrophilic center
3 2 3 1
Determine the number of signals that would be generated in the 1 H NMR spectrum of each of the following compounds, and predict the splitting pattern and integration of each signal.
d. Enol, ketone, tautomers
During the acid catalyzed hydration of an alkyne an intermediate forms called a(n) _______, which rapidly interconverts to form a more stable _____. The two structures are said to be ___________.
a.more, increases, greater
Elimination reactions to form alkenes are favored at high temperatures because there are ______ product molecules than reactant molecules, so that the entropy of the system ________. At higher temperatures this results in a ______ impact of the T∆S term on the overall Gibbs free energy.
E. only A and C
Enantiomers are
a. super, same, achiral b. left is S and right is R-nonsuper, enantiomers, chiral c. both R-super, same, chiral d. nonsuper, constitutional, chiral e. nonsuper, diastereomers, achiral f. super, same, achiral g. nonsuper, diastereomers, chiral h. nonsuper, enantiomers, chiral
For each pair of molecules, determine whether they are "superimposable" or "nonsuperimposable." (models can be helpful) Now determine the relationship between each pair of molecules (same, constitutional isomers, enantiomers or diastereomers). Lastly is each "chiral" or "achiral"?
b. A = 3, 4; B = 3, 4; C = 3, 4
For each reagent, predict all the major product(s).
B. 2 *first and last one
How many are constitutional isomers of each other?
C. 3 1, 3 and 5
How many are diastereomers?
Again plane of symmetry B. 2
How many different proton chemical environments does this molecule have?
B. 2 Mirror image so 2 instead of 3
How many different proton chemical environments does this molecule have?
2 4 3 3 1 3
How many different signals would each of the following molecules produce in a 1 H NMR spectrum?
D. 4 * the one with the c=o is not one
How many of the below are constitutional isomers?
A. 1 only C
How many pairs of enantiomers?
C. 3: Hs in CH2 are diff bc of the double bond
How many signals should appear in the 1H-NMR spectrum of the molecule below?
5
How many signals will be in the 1 H NMR spectrum of
b. Z
Identify the configuration of the alkene bond highlighted in red in the following compound.
C. D and G
Identify the electrophilic centers in the following molecules.
D. A, C, E, F and H
Identify the nucleophilic centers in the following molecules.
e) will not be effected, doubles
In an SN1 reaction, if the nucleophile concentration doubles, the reaction rate ________. In an SN1 reaction, if the substrate concentration doubles, the reaction rate ________.
B. CH3Cl: closest to 12 ppm bc Cl is the most electronegative
In which compound will the proton signal be shifted the most DOWNFIELD?
e. 1, 4 and 5
In which of the following reactions syn addition is part of the mechanism?
A. plane of symmetry C.no D. not a meso compound
Is this compound a meso compound?
E
List ALL the major products of the following reaction?
B. I, C *elim, OH Mark
List the correct order of reagents to accomplish the following synthesis.
D. L, H, E *ant Mark
List the correct order of reagents to accomplish the following synthesis.
LGs
Mesylates, tosylates, and triflates are excellent ____ •(OMs, OTs, and OTf)
S
S or R?
a) Methyl *tertiary is nonexistent/unreactive
SN2 reactions proceed fastest with ________ substrates.
a) inversion *racemic=1/2R and 1/2 S
SN2 reactions where there is only one stereocenter and the leaving group is attached to that stereocenter will produce ________ products.
a. Singlet & triplet A = singlet C = triplet
Signals A & C would appear as ? respectively?
B
Starting with Acetylene, what would be the appropriate set of reagents to produce 2-methyl-4-nonyne?
a) weak, stable *weak bases are very stable
The best leaving group produces a _________ base that is a(n) _________ anion.
SN2 rxn
The concerted mechanism involves breaking of the bond to the leaving group and making of the bond to the nucleophile at the same time backside attack happen at the same time the Nuc does a backside attack, and only the inversion of configuration product is obtained.
a. Markovnikov
The overall results of an Oxymercuration-Demercuration reaction produces a ______ addition.
D) -OH is a poor leaving group, as the base formed, OH-, is a strong and unstable base *secondary=>WB, strong nuc, SN2
The reaction shown below has a very poor yield. Which of the following statements is true concerning the poor reaction efficiency?
SN1 rxn
The stepwise mechanism the leaving groups leaves first, to give a carbocation intermediate, followed by nucleophilic attack typically more of the inversion product is observed
C
To which compound does the following NMR spectrum belong?
B
What are the product(s) of this reaction?
d. A and d
What are the product(s) of this reaction?
D
What are the products of the following reaction?
E. A, B, C, D
What are the products of the following reaction?
c.A, E
What are the products of the following reaction?
D)F- *stronger nuc=stronger base
What halide is the strongest nucleophile in a polar aprotic solvent?
A. R
What is the configuration?
a. (3S,4S)-3-bromo-4-chlorohexane
What is the correct IUPAC name for the following structure?
c. (E, 5S)-5-isopropyloct-2-ene
What is the correct IUPAC name for the following structure?
d. 2,8-dimethyl-3-decyne
What is the correct IUPAC name for the following structure?
c
What is the correct mechanism and product for the following reaction?
c. 1) MCPBA 2) H3O+
What is the correct order of reagents needed for the following reaction?
B. A, F
What is the correct order of reagents needed for the following transformation?
D. A, G, E
What is the correct order of reagents needed for the following transformation?
D. E, C, D
What is the correct order of reagents needed for the following transformation?
b
What is the major product for the following reaction?
e
What is the major product for the following reaction?
A
What is the major product of the following reaction?
A-strong nuc, resonance stabilized WB, SN2
What is the major product of the following reaction?
B- secondary=>strong nuc SB, elim-Ez major and SN2 minor
What is the major product of the following reaction?
B-SN1 *a is E1 and d is minor
What is the major product of the following reaction?
B-hindered base
What is the major product of the following reaction?
C
What is the major product of the following reaction?
C In this problem the reaction proceeds via an E1 mechanism. Upon formation of the secondary carbocation a methyl group will migrate to create a tertiary carbocation. Then the Zaitsev product will form.
What is the major product of the following reaction?
C SB, strong nuc and ∆promotes elim, nonnuc base hindered a is minor
What is the major product of the following reaction?
D- teritary reagent=>WB strong nuc = SN1
What is the major product of the following reaction?
D-unhindered base *b is minor, c is trans and e is not possible
What is the major product of the following reaction?
E- primary reagent=>WB strong nuc = substitution -SN2
What is the major product of the following reaction?
C Anti mark D tautomerizes to C
What is the major product of this reaction?
E Mark HOH
What is the major product of this reaction?
b. Substitution, A=Electrophile, B=Nucleophile, C=Leaving group
What is the name given to the following class of reactions, and what word would best represent the species A, B, and C?
a
What is the product (in addition to its enantiomer) of the following reaction?
B
What is the product of the following reaction?
d. b, c *unsymm trans=enantiomers
What is the product of the following reaction?
B. enantiomers
What is the relationship between the following molecules represented in their Fischer projections?
e) C and D
What is the relationship between the molecules?
B. configurational isomers
What is the relationship between...
D. the same molecule
What is the relationship between...
E. A and B mirror nonsuperimposable (rotate flat drawing=not the same)
What is the relationship between...
E. A and B mirror image, nonsuperimposable
What is the relationship between...
a d and e
What reagent is needed for the following reaction?
b. Na in NH3 (l)
What reagent is needed for the following reaction?
c. H2/Pt *Pb, Ni
What reagent is needed for the following reaction?
a
What will be the major product(s) of the following reaction?
c
What will be the major product(s) of the following reaction?
A. molecule (a)
Which Fischer projection below corresponds to this molecule?
A
Which are diastereomers?
D. A, D, E
Which bases are strong enough to deprotonate the following compound efficiently?
d) I- *F- is the worst LG
Which is the best leaving group?
E. all of the above
Which of the following are true about:
D. A and E
Which of the following carbocations will rearrange?
E. C and D *carbon is a strong base
Which of the following curved arrow mechanistic steps would you expect to be irreversible?
E. all of them
Which of the following curved arrow transformations do not follow the rules for curved arrow drawings?
c. C *aprotic=no H bond
Which of the following is a polar aprotic solvent?
d. b, f, g, h a=trans b=cis c=neither d=trans e=neither f=cis g=cis h=cis
Which of the following represent cis isomers?
C. A, B, C, D, F
Which of the following structures will form alkynes upon treatment with excess NaNH2 followed by H2O?
C: protons on the benzene show up about 6.5-8.5 ppm, d would show up about 2.5-4.5 bc of Cl, so C shifts the most bc closest on the ring to the Cl
Which proton will have the greatest chemical shift?
C a=most downfield b=4.2-2.5 ppm c=1.5-2.5
Which protons would appear most upfield in the NMR?
B
Which represents the chair conformation of the following with both groups axial?
E OH is left to M
Which represents the ring flip of the structure?
D
Which sequence of reagents will complete the following synthetic sequence? (? = nu/ν )
d. 1. Hg(OAc)2, CH3OH, 2. NaBH4 *Markovnikov, no rearrangement, mercuration
Which set of reagents will effectively complete the following reaction?
c. 1) MCPBA 2) H3O+
Which set(s) of reactants will not form the expected product?
A
Which spectrum corresponds to
b) Increased temperature
__________ increases the likelihood of elimination occurring instead of substitution.
no
are these two enantiomers?
E2
concert, 2 things have to come together at the same time, bimolecular, 2nd order kinetics loss of leaving group vs. loss of beta-proton AND leaving group to form double bond rate = k [alkyl halide] [base] occurs when substrate is sterically hindered regioselective
top one: non enantiomers (mirror images but superimposable) bottom one: enantiomers (mirror images, non superimposable)
how are the molecules related
.
i
(the Zaitsev product)
more stable alkene ______ produced as the major product
(2S,3R)-3-bromo-2-chloropentane
name include S/R
(S)-2-chlorobutane
name include S/R
(S)-3methylhex-1-ene
name include S/R
*has plane of symm and meso (1R,3S)-1,3-dibromocyclohexane or cis-1,3-dibromocyclohexane or meso-1,3-dibromocyclohexane
name include S/R
stereoisomers
same molecular formula and constitution but diff spatial arrangements of atoms
meso compound
those molecules who HAVE chiral centers... but aren't chiral (because of a plane of symmetry that passes through the molecule).
E1 mechanism
through a two-step (stepwise) mechanism unimolecular rate determining step is the formation of the carbocation intermediate •will always give the most stable alkene as the major product, the most substituted alkene regioselectivity stereoselective
enantiomers nonsuperimposable mirror images chiral carbon stereocenter OFTEN but not always, enantiomers have a chiral center
what is the relationship bt these molecules
enantiomers of trans-1,3-dibromocyclohexane left: (1R,3R)-1,3-dibromocyclohexane right: (1S,3S)-1,3-dibromocyclohexane
what is their relationship name include S/R
diastereomers nonsuperimposable nonmirror images
what type of isomers?
SN1 mechanism
• proceeds through a two-step (stepwise) mechanism first-order kinetics formation of the carbocation the is rate determining step. •Since the formation of the carbocation requires only ionization of the substrate, the rate of it's formation depends only on the substrate, and so the rxn follows first-order kinetics the leaving group first leaves to form a carbocation intermediate, followed by nucleophilic attack
reversible irreversible
•All proton transfers are ____. •But, if the pKa difference is 10 units or more, it can be considered ___
addition elimination
•At lower temps, enthalpy dominates, and ____ reactions are favored •At higher temps, entropy dominates, and ____ reactions are favored
irreversible
•Carbocation rearrangements are generally ____
aprotic protic *aprotic raise E results in low Ea *protic stabilize carbocation intermediate, results in lower Ea
•For SN2 rxns, a polar ______ solvent is best • For SN1 rxns, a polar _______ solvent is best
axial
•Given the anti-periplanar requirement, E2 elimination can only occur when the leaving group is in the ____ position.
ID ID SI SI CS
•Identify the following pairs as either constitutional isomers, stereoisomers, or identical structures
irreversible
•If the attacking nucleophile is a poor leaving group, it will essentially be an _____ attack
reversible
•If the attacking nucleophile is also a good leaving group, it will be a ____ attack
LG
•The better the _____, the faster the SN1 or E1 rxn (like Cl, Br, and I (best) are faster than F)
reversible
•The loss of a leaving group is virtually always ____
alcohols
•The mechanism will be either SN1 or SN2, depending on the substrate. 1˚ ___ react via SN2, but 2˚ and 3˚ ____ react via SN1
Configurational isomers
•Type of stereoisomer - •Stereo - Greek word meaning "solid", that has come to be associated with 3D objects •In the case of stereoisomers, "stereo" means "3D space" •Atoms connected in the same order(linked to the same neighbors) BUT are in a different spatial relationship to each other
Electrophile
•electron deficient species, can accept a pair of electrons • are Lewis acids •Carbocations and partially-positive atoms
Nucleophile
•electron rich species, can donate a pair of electrons - are Lewis bases -More polarizable = stronger ____
(the Hofmann product)
•less substituted alkene ________ is the minor product.
constitutional isomers
•same degrees of unsaturation •same number of C, N, O, (H), etc. •different connectivity -if you can flip 'em, rotate 'em, rotate around bonds, & they look the same they're NOT ______
