chm 235 exam 3

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 ________ .

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?

a) The central C atom

By considering the polarity, which atom would be the most "partially positive" in ethyl bromide?

e) trigonal planar

Carbocations have __________ geometry.

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.

b. A = 3, 4; B = 3, 4; C = 3, 4

For each reagent, predict all the major product(s).

b. 2, 2, 1

Going from left to right, classify each halide as 1o, 2o or 3o

c. achiral, racemic

Hydrohalogenation mechanisms proceed through a carbocation intermediate, which is _________. Therefore the products of these reactions generally are _________.

b. Z

Identify the configuration of the alkene bond highlighted in red in the following compound.

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 ________.

e. 1, 4 and 5

In which of the following reactions syn addition is part of the mechanism?

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)

c. 2>3>4>1 *arrows are reversed on accident so 1 is the most E and 2 is the lowest

Rank the following alkenes from lowest energy to highest energy.

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.

c. Anti-Markovnikov and Syn

The Hydroboration-Oxidation reaction produces a _______ addition

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.

c) tertiary > secondary > primary > methyl

The general order for stability of carbocations is __________.

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.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. (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

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?

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?

d. b, c *unsymm trans=enantiomers

What is the product of the following reaction?

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?

C. 3 weak nuc and WB = SN2 The phenolate anion acts as a strong nucleophile, but is stabilized by resonance, so it is a much weaker base than the negatively charged oxygen in an alkoxide, so it reacts with 2o alkyl halides at lower temperatures via SN2 reaction. Option d would imply a loss of stereochemistry via an SN1 reaction, which can occur, but would be a minor product.

What would be the major product of the following reaction?

a) The central C atom *partially - attracted to partially +

Which atom in ethyl bromide would SH- be most attracted to?

D. A, D, E

Which bases are strong enough to deprotonate the following compound efficiently?

c) The C-Br bond

Which bond is polar in ethyl bromide?

d) I- *F- is the worst LG

Which is the best leaving group?

c. C *aprotic=no H bond

Which of the following is a polar aprotic solvent?

C. A, B, C, D, F

Which of the following structures will form alkynes upon treatment with excess NaNH2 followed by H2O?

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?

b) Increased temperature

__________ increases the likelihood of elimination occurring instead of substitution.

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

(E) 3,4,5,5-tetramethylhept-3-ene 1-ethylcyclohexene (E)-2-chloro-2-heptene (R)-3-bromocyclohexene (R)-3-chloro-1-methylcyclepentene 4-bromo-3,3-dimethyl-4-propylheptane (E)-4,5-dibromo-2,2,7-trimethyloct-4-ene

give the IUPAC name skip C

(the Zaitsev product)

more stable alkene ______ produced as the major product

addition elimination

•At lower temps, enthalpy dominates, and ____ reactions are favored •At higher temps, entropy dominates, and ____ reactions are favored

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.

Markovnikov addition

•Hydrohalogenation is regioselective for ____ •The halogen is generally installed at the more substituted carbon

Hydrohalogenation

•The Markovnikov product is formed through a lower energy (i.e. faster) transition state.

LG

•The better the _____, the faster the SN1 or E1 rxn (like Cl, Br, and I (best) are faster than F)

alcohols

•The mechanism will be either SN1 or SN2, depending on the substrate. 1˚ ___ react via SN2, but 2˚ and 3˚ ____ react via SN1

Oxymercuration-Demercuration

•is an alternative -Markovnikov addition of H and OH -No rearrangements occur

(the Hofmann product)

•less substituted alkene ________ is the minor product.

Hydroboration-Oxidation mechanism

•stereospecific: only syn addition occurs