•write clearly! midterm #2 practice test #12 chemistry 234, midterm #2 practice test #1 - 2 - name...

1

Ian R. Gould

PRINTED FIRST NAME

Person on your LEFT (or Aisle)

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

CHEM 234

PRINTED LAST NAME

H/H ~1.0

Eclipsing

H/Me ~1.4

Me/Me ~2.6

Me/Me ~0.9

Et/Me ~0.95

i-Pr/Me ~1.1

t-Bu/Me ~2.7

Gauche

Me/Et ~2.9

Interaction Energies, kcal/mol

ASU ID or Posting ID

Person on your RIGHT (or Aisle)

• PRINT YOUR NAME ON EACH PAGE!

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C NR2

RC CRR2C CR2

Aromatic

CR OHO

C X

R NH2R OH

aminealcohol

3Y > 2Y > 1Y

020406080100120140160180200220

–H2C X

–H2C NR2

–OCH2–

01234567891011

C CHC HO

CR OHO

Aromatic Ar HAlkylmainly 8 - 6.5

C CH2

C CH3

O

3Y > 2Y > 1YAlkyl–OCH2–

CO

(δ, ppm)

variable and condition dependent, ca. 2 - 6 δ

R C N

O H C N

CN

CC

H

C ON H

C H

C N

O

HCO

CH

C CH

COR

ON H

C H

CO

O H

C O HO

CNR2

O

3000–3100

2850–2960

3300

broad ~3300

broad with spikes ~3300

2200

broad ~30001710

2200

1650

2720–28202 peaks

1735

1600–1660

1680

range of valuesbroad peak

small range usuallystrong

1600

CH

CH

C CHH

CH

CH

CH

CH

H

H

H

H

Approximate Coupling Constants, J (Hz), for

1H NMR Spectra

~7

~10

~2

~15~2

~8

Infrared Correlation Chart

NMR Correlation Charts

3000 200025003500 1500(cm-1)

THIS IS A CHM 234PRACTICE EXAM

MIDTERM #2PRACTICE TEST #1

the exam cover sheets look kind of like this

2

CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 2 - NAMEQuestion 1 Give the IUPAC name for the following compounds. Be sure to use cis/trans, E/Z or R/S where appropriate.

OCH2CH2CH3

(3R)-propoxycyclopentene1 2

3

5 4H

Question 5 Sodium borohydride (NaBH4) reduces only aldehydes and ketones. Lithium aluminum hydride (LiAlH4) will reduce aldehydes and ketones and also esters and carboxlic acids. Give a BRIEF explanation for the different reactivities of NaBH4 and LiAlH4. Include the term "Lewis base" in your explanation.

LiAlH4 is more reactive than NaBH4 because the electrons in the Al-H bonds are higher in energy than those in the B-H bond, since Al is larger than B. LiAlH4 is thus the stronger Lewis base, its reactive electrons are higher in energy

Question 4.a) Give the organic reactant and the Grignard reagent you would use to make the bond indicated by the dashed line in the provided structure (do not include the aqueous acid workup step, stereochemistry is ignored in this question)

HO

Ph

O+Ph MgBr

c) Explain why the Grignard reaction shown would NOT work

Ph

HO

XO+Ph MgBr

the Grignard would have to attack the MOST substituted side of the epoxide, which is slower than attacking the least substituted side

b) Give the organic reactant and the Grignard reagent you would use to make the bond indicated by the dashed line in the provided structure (do not include the aqueous acid workup step, stereochemistry is ignored in this question)

HO

Ph

O

+Me MgBr

Ph

3

Question 5 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement3) Briefly explain whether the a solution of the product would be optically active or not4) Pay attention to stereochemistry including racemic mixtures unless specified

b)

a)

CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1 - 3 - NAME

d)

c)

O

CN

CNO

CNCN

heat+addition, achiral reactants, meso

product formed, not optically active

Na+ –OCH3

CH3OH

O OH

OCH3

addition, chiral reactants, single

enantiomer formed, optically active

HH

–OCH3

SN2

the expected Walden inversion occurs "pushes" the Me and H up

NBS, hνBr substitution, achiral

reactants, achiral product, not

optically active

1. Hg(OAc)2, CH3OHCH3

2. NaBH4

CH3

OCH3

neitheradditionnot opically active, achiral

Question 6. Provide the missing reactants for the following Diels-Alder reaction.

CNCN+ (±)

heat

4

CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #1- 4 - NAME

Δ

1) draw the arrow-pushing that describes formation of the PROVIDED product2) How many electrons are involved in the reaction?3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the ring closing be disrotatory or conrotatory?4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the transition state be Hückel or Möbius?5) Is PROVIDED PRODUCT allowed or forbidden and why?

6 electrons

Möbius

Forbidden, the allowed product of a 6-electron electrocyclic ring closing reaction would proceed via an aromatic Huckel transition state and would be disrotatory, not Mobius/conrotatory

Conrotatory

Question 5. The purpose of this question is to determine whether the provided product is allowed or forbidden

Question 6) For the following ion, draw all reasonable resonance contributors, draw an "actual" structure that includes partial bonds and partial charges (use δ to indicate partial charges), and draw the HOMO and LUMOs on TOP of the provided structures

the pi-molecular orbitals extend over the conjugated part of the structures and does not include any sp3 hybridized atoms

HOMOand

resonance

δδ

LUMO

"actual" structure

Question 7. Show how you would synthesize the target compond on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.

Br

ONBS/hν

NaOMe

1. NaH2. PrBr

OH

1. BH3.THF2. –OH/H2O2

(±)

(±)

5


Question 8) Explain why the products of the following reaction are an alcohol and a bromide, rather than two bromides, Draw a mechanism to support your reasoning

O OH Br+

HBrH Br

O

H Br

LA/BA

LB/BB

LB

LAthese are the final products

OH Br+

H BrLA/BA

LB/BB

OH2can't do a substitution at an sp2 hybridized

carbon via either SN1 or SN2, the

only possible further reaction is loss of

proton to reform the alcohol

X

SN2

NC

CN+

H2C CH2N

NC CN

Δ (±)

4(s) + 2(s) suprafacial/suprafacial allowed

* *

LUMOHOMO NC

CN

1 node

H2CN

CH2

CH3CH3

Question 9). Give the curved arrow-pushing and the ALLOWED product of the following cycloaddition reaction

H2CN

CH2

CH3

1 node

b) Give a pictorial representation of the wavefunction of the HOMO ON TOP OF THE STRUCTURE below for A, indicate the number and positions of any vertical nodes (ignore horizontal nodes)

c) Give a pictorial representation of the wavefunction of the LUMO ON TOP OF THE STRUCTURE below for B, indicate the number and positions of any vertical nodes (ignore horizontal nodes)

A

B

the ALLOWED product of the reaction must have two bonding interactions in the transition state, consideration of the wavefunctions of the HOMO and the LUMO indicates that suprafacial/suprafacial reaction is allowed, thus the 2 -CN groups start trans- and are also trans- in the product

d) Give a brief justification for the stereochemistry in your allowed product, you must include the following terms in your justification: suprafacial and/or antarafacial, HOMO, LUMO, bonding and/or anti-bonding

6


Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate.

START OF PRACTICE TEST #2

b) HOO

12

3 45

6 4-methoxy-3-methylhex-(3Z)-en-1-ol

(alcohol highest priority functional group, determines numbering)

ethers are alway just "alkoxy" substituents

a)Et

NO2

Br

1-bromo-2-ethyl-4-nitrobenzene

OHHBr

MeOH (solvent)OMe

OH2OMe

H OH

Me

O

Me

H

LBLA

LB/BB

LA/BA

LA/BA

LB/BB

HO

MeH

when dissolved in MeOH, HBr is essentially completely dissociated, just the same as it is in H2O

Question 2. Give a complete curved arrow pushing mechanism, and...1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they are also Brønsted acids/bases (LA/BA, LB,BB)2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM

4 steps

7

Question 3 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) State whether the OVERALL reaction is Addition, Elimination, Substitution or Rearrangement3) Briefly explain whether the a solution of the product would be optically active or not4) Pay attention to stereochemistry including racemic mixtures unless specified

b)

a)


d)

c)

+CF3

heatF3C

(±)

addition, achiral reactants, racemic mixture, not

optically active(this is about as tricky a

Diels-Alder reaction I can come up with!)

OH

OH

1. MCPBA

2. H3O+

oxidationnot optically active, racemic mixture formed(±)

Br

1 Equiv. Na+ –CN

CNsubstitution, chiral reactants, single


Br BrSN2 at allylic,

specifially benzylic carbon is fast

O Na+ –OEt/EtOHOH

OEt

H H addition, chiral reactants, single


not protonated, attack least

substituted side

Δ

1) draw the arrow-pushing that describes formation of the product2) How many electrons are involved in the reaction?3) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the ring opening be disrotatory or conrotatory?4) FOR THE PROVIDED PRODUCT (which may or may not be allowed), would the transition state be Hückel or Möbius?5) Is THE REACTION SHOWN allowed or forbidden, and why?

4 electrons

Hückel

Forbidden, the allowed product of a 4-electron electrocyclic ring opening reaction would proceed via a Mobius transition state and would be conrotatory, not Huckel and disrotatory

NCH3

CF3F3C

H H NCH3

HH

F3C CF3

Disrotatory

Question 4) The purpose of this question is to determine whether the provided product is allowed or forbidden

8


CN

CNCN

CN

+(±)


N N N N NN

Question 5. For the following structure:a) Draw all additional reasonable resonance contributortsb) Draw on TOP of the structure a pictorial representatrion of the wavefunction of both the HOMO and the LUMO, give the number of vertical node (only) and indicate their positions.

N N

resonance contributors

HOMO

6 electrons in the π-system

2 vertical nodes

node node

N N

LUMO3 vertical nodes

node nodenode

Question 6. Rank the following structures in order of increasing rate of reaction in a Diels-Alder reaction with fumaronitrile (shown), and give a brief explanation that includes the terms "donating group", "withdrawing group", "energy of the electrons", "HOMO".

O

––– ––– –––< < CAB

the dienes differ by the substituents that are circled, the energy of the electrons in the diene, specifically those in the HOMO, are raised by donating groups and lowered by withdrawing groups, raising the energy of the electrons in the HOMO decreases the HOMO/LUMO gap (the LUMO on the fimaronitrile), which decreases the reaction activation energy and increases the rate

C has a strong donating group (non-bonding electrons on N) and a weak donating group (the alkyl chain), it reacts fastestA has a withdrawing and a strong donating group (non-bonding electron on the nitrogen), it is intermediateB has a withdrawing and only a weak donating group (the alkyl chain), it is slowest

NH

NH

ONH

A B C

withdrawing

strong donating weak donating

strong donatingwithdrawing

weak donating

CN

NCfumaronitrile

9

Question 7. Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.


NBS, hν

Ph Ph

Ph PhBr

Ph Ph

t-BuO–+K

Ph Ph

OH

1. BH3.THF

2. H2O2/ –OH

Ph Ph

O– +Na

Ph Ph

O

Br

Na H

CN

NC+

H3CO H3COCN

CN(±)

H3COCN

CN(±)OR..

heat

Question 7 (20 pts.)a) Give the curved arrow-pushing and the ALLOWED product of the following cycloaddition. State whether the product is achiral, a mso compound, a pure enntiomer or a racemic mixture

A B

b) Draw the HOMO for reactant A and the LUMO for reactant B on top of the structures below, understanding that it may not be possible to get the geometry of the orbitals with respect to the structures exactly correct because the structures have to be drawn flat on the paper

HOMO LUMO

c) does the allowed reaction proceed suprafacial/suprafacial or suprafacial/antarafacial?suprafacial/suprafacial

H3COCN

NC

10


Question 1 Give the IUPAC name for the following compound. Be sure to use cis/trans, E/Z or R/S where appropriate.

START OF PRACTICE TEST #3

OH1 2

3 4 56

7

(6R)ethoxyhept-(2Z)-en-4-yn-2-ol

*OEt

O

HCl cat.

OH

O

H

OH OHO

H

OHOLA/BA

LA

LB

LB/BB

LA/BA

H Cl

LB/BB

when dissolved in i-PrOH, HCl will be partially dissociated, an so it is not obvious which acid species, HCl itself or protonated alcohol will be responsible for

protonation of the epoxide, you can use either, however, the i-PrOH solvent will be present at MUCH higher concentrations than the conjugaye base anion from HCl, and therefore deprotonation occurs to i-PrOH (even if the proton eventually gets

returned to form HCl)

Question 2. Give a complete curved arrow pushing mechanism, and...1) Indicate the Lewis acid/Lewis base (LA, LB) at each step as appropriate, and whether they are also Brønsted acids/bases (LA/BA, LB,BB)2) GIVE THE NUMBER OF STEPS IN YOUR MECHANISM

OH

11

Question 4 For each reaction1) Provide the missing reagents/conditions or major organic products as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified3) State whether a solution of the product(s) would be optically active or not and give a brief explanation

b)

a)


c)

1 Equiv. HBr Br

(±)

achiral reactants, racemic product,

not optically active

reaction at THIS alkene fastest because the primary intermediate is a 3° cation

heatCO2CH3

CO2CH3

CO2Me

CO2Me

+

achiral reactants, meso product, not optically active must rotate to s-cis before reaction

=CO2Me

CO2Mesame

as

O Na+ –OEtEtOH (solvent)

EtO

OH achiral reactants, achiral product

formed, not optically active

epoxide NOT protonated, attack least substituted side

DCl

D

(±)(thermodynamic control conditions)

achiral reactants, racemic mixture,

not optically activeD = deuterium = "labelled hydrogen"

Cl

ClD deuteriate here first, makes most stable intermdiate

d)

Question 5) Indicate which reaction is more exothermic, give an explanation

A B

BrBrBr

Br

the two alkene products are structural isomers, when comparing structural isomeric alkenes the more substituted isomer is the more stable (Sayetzeff/Zaitzeff etc.) rule, formation of the more stable isomer is more exothermic, reaction B is more exothermic than reaction A

only 1 H atom on the C=C bond, 3 substituents, this alkene is more

substituted,more stable

3 H atoms on the C=C bond, 1 substituent, this alkene is less substituted, less stable

HH

HH

12



NBS, hν

Br

t-BuO–+K

O

O

O

O

O

O

H

H

O

O

O

H

H

HO

1. Hg(OAc)2/H2O2. NaBH4

Δ

ignore stereochemistry here

meso compound

S Δ

Question 6) The ylide below undergoes an electrocyclic ring closure reaction

t-Bu

a) give the curved arrow-pushing that accounts for product formationb) draw the product, paying special attention to relative stereochemistry of any substituentsc) indicate the locations of any chiral (asymmetric) carbons atoms with the symbol, and state whether it is racemic, a meso compound or achirald) give the NUMBER of electrons involved in the reactione) state whether the allowed reaction proceeds via a Huckel or a Mobius transition statef) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing

g) Draw a pictorial representation of the HOMO on top of the structure below, give the number of vertical nodes (only) and oindicate their positions

t-Bu

conrotatory

*S t-But-Bu

*H H

*

Mobius4

*

S

t-Bu

t-Bu1 node

13


Br CH3OH

OCH3H

O CH3

H

O HH3C

OH

H3C

OCH3

H

H3COOCH3

kineticthermodynamic

O CH3

H

Question 7. a) Give a full curved-arrow pushing mechanism for formation of both products of the provided reaction. One of these products would be formed preferentially under conditions of kinetic control, the other preferentially under conditions of thermodynamic control, indicate which is which. Indicate the Lewis acid and base at each step and whether they are also Bronsted acids/bases.

b) Give a reaction energy diagram for both reactions in the SAME DIAGRAM

reaction coordinate

energy

Brboth

‡‡

‡

‡

‡ OCH3

H3CO

O HH3C

OH

H3C

CH3OH

kinetic

thermodynamic

kinetic

thermodynamic

heat

LB/BB

LA/BA

LA/BA

c) Give a brief explanation of how temperature is related to kinetic and thermodynamic controlat all temperatures the kinetic product is formed faster, at lower temperatures the reactions will be more IRREVERSIBLE, the kinetic product product will predominate, at higher temperatures the reactions will become more REVERSIBLE and the lower energy thermodynamic product can be formed and will start to accumulate

LB/BB

+A B

14


Δ

CN

+

suprafacial/antarafacial

NC

CN

CN(±)

Question 8. The purpose of this question is to determine whether the provided product of the cycloaddition reaction given below is allowed or forbidden (there are several possible products of this reaction, we will focus our attention on this one to see if it is allowed)

a) give the curved arrow-pushing that accounts for product formationb) draw the HOMO and LUMO ON TOP OF THE structures as indicated above, and give the number of vertical nodes and clearly indicate their positionsc) IGNORING THE PROVIDED product for now, use the information from the F.M.O.s to decide whether the ALLOWED reaction would be suprafacial/suprafacial or suprafacial/ antarafacialyour answer________________________________d) Using the sterochemistry of the PROVIDED PRODUCT, decide state whether the it was formed via suprafacial/suprafacial or suprafacial/ antarafacial cycloadditionyour answer________________________________d) state whether the PROVIDED PRODUCT is allowed or forbidden, and give a BRIEF explanation that mentions the frontier molecular orbitals.

HOMO

LUMO

suprafacial/antarafacial

The provided product is ALLOWED, it is formed in suprafacial/antarafacial reaction and the phases of the HOMO and LUMO at the relevant carbons result in two bonding interactions for such a reaction

1 node

1 node1 node

non-aromatic

sp3

anti-aromatic4 electrons 4 electrons

anti-aromatic

8 electronsN

anti-aromatic

8 electrons

these electrons are in sp2 hybrid A.O.

Question 9) Classify the following structures as aromatic, non-aromatic or anti-aromatic, assume all structures are as flat as possible, AND give the number of electrons involved in the conjugated system

suprafacial on this reactant (shown with both bonds being made to the bottom of the carbon atoms)

antarafacial on this reactant (shown with one bond being made to the top of one carbon atom and one bond being made to the bottom of the other carbon atom)

CIS-

TRANS

the reaction is antarafacial on the lower reactant because the cis-stereochemistry of the substituents becomes trans- in the product (this would not be included as part of the answer)

15

CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 2 - NAMESTART OF PRACTICE TEST #4

OMe

Me

Me

Me

OH

Me

Me

H

OH

H

H

H

Oi-Pr

i-Pr

i-Pr

i-Pr

––– ––– ––– –––< < <D A B C

Question 2) Rank the following in order of icreasing rate of reaction in a base catalyzed hydrolysis reaction (addition of water in the presence of hydroxide) and give a brief explanation (hint, think abouyt the slowest, rate determining step for base catalyzed hydrolysis)

A B C D

The rate determining step is hydroxide as Lewis base in SN2 type attack on carbon of the Lewis acid epoxide. This process is subject to steric hinderance, hence the order given.

OHOH OH OH

slow slowestfastestslowish!!

Question 1. Provide TWO Grignard reactions, A and B, that can be used to make the provided target structure. Give the organic reactant and the Grignard reagent that would be used, you do not need to specify the aqueous acid workup step, but you musty specify which of the C-C bonds is being made in the provided target structure.

OH

H

OMgBr+

H

O

BrMg+

OH

OHO

CH3BrMg+

A)

B)

OR...

Question 3 Show how you would synthesize the target componds on the right from the starting compounds on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.

CH3 CH2OH CH2 CH2OHCH2CH3

CH3 CH2Br CH3 CH2MgBr

O1.

2. H3O+

Mg.THF

PBr3

16

Question 4. For each reaction.1) Provide the missing reagents/conditions or major organic products as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified

b)

a)


1. MCPBA

2. MeOH/HCl (cat.)

(ignore stereochemistry)

OH

OMe

+H3C CN

heatH3C

CN

(±)

+heat

For BOTH of the reactants A and B:b) Give a pictorial representation of the requested frontier molecular orbital as requested on top of the provided structurec) Give the number of electrons in the conjugated system that are relevant to the reactiond) State whether the allowed reaction is suprafacial or antarafacial

CNO

CH3

CC

CH3

H3C

H

H NO

H3C

CH3

Question 5) a) Give the curved arrow pushing and the product of the following reaction. Pay attention to stereochemistry and state whether a solution of the product(s) would be opticlly active or not.

A BCH3

(±)racemic mixture

formed, not optically active

CNO CH3

4 electronsCC

CH3

H3C H

H

A: HOMO

suprafacial 2 electrons

B: LUMO

suprafacial

not a racemic mixture, meso

compound

c)

d)1. MCPBA

2. H2O/HCl(cat.)

HO

OH

EtMgBrBr

17


NBS/hν

Br

MgBr

Mg.THF

O

H

O1.

2. H3O+

OH

(ignore stereochemistry)

1. NaH2. PrBr

Question 6. Show how you would synthesize the target compound on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.

essentially same as non-bonding

Question 7. Consider the energy of an electron in each of the following π-molecular orbitals AND a p atomic orbital on a carbon atom and rank them in order of increasing energy. Two of the energies will be essentially equal, as indicated below

A

B D

D

C

–––<

E

F (p atomic orbital)

A–––< C––– F–––< E–––< B–––lowestenergy

highestenergy

~

most bonding interactionsmost anti-bonding interactions

non-bonding by definition

roughlythe

same

18


Question 8) Rank the following reactions, A, B and C, in order of INCREASING exothermicity. Give a BRIEF explanation

2 H2A

B2 H2

C

lowestexothermicity

highestexothermicity

< < BA C

the products are all the same, the energies at the end of all reactions is thus the same, the difference is in the reactants. A and C are conjugated, electrons are lower in energy, the reactants in A and C start lower in energy, thus less exothermic than B, the diene is more substituted in A compared to C, diene A is thus more stable, lower in energy, reaction A is least exothermic

2 H2

Δ

Question 9) The structure below undergoes an electrocyclic ring opening reaction (remember, D means deuterium, an isotope of hydrogen that is often used as a labelled hydrogen atom)

a) give the curved arrow-pushing that accounts for product formationb) draw the product, paying special attention to relative stereochemistry of any substituentsc) give the NUMBER of electrons involved in the reactiond) state whether the allowed reaction proceeds via a Huckel or a Mobius transition statee) state whether the allowed reaction proceeds via a conrotatory or a disrotatory ring closing

disrotatory

Huckel6

D

D

D

D

CN+

heat

CN(±)


19

CHEMISTRY 234, MIDTERM #2 PRACTICE TEST #4 - 6 - NAMEQuestion 12) Provide a detailed (arrow pushing) mechanisms for the following transformations. draw all important resonance structures. For each intermolecular step, identify the Lewis acid and base (LA/LB) as appropriate, and whether they are also Bronsted acids/bases (BA/BB), give the number of steps in your mechanism (hint BOTH SN1 and SN2 can occur at allylic carbon atoms)

H Br

conc. HBrO Ph

O PhH

heat

OH

Ph+

Ph

Br

OH + PhBrLB/BB LA/BA

LA

LB

OH

Ph

O

Ph OH

Ph

O– +Na

Ph

O

PhPCC/CH2Cl2

1. EtMgBr2. H3O+

NaH

Br

the last 2 stepscan also be shown as one reaction

with the 1. 2. notation

Question 13. Show how you would synthesize the target compond on the right from the starting compound on the left. Show reagents and conditions, and the structures of important intermediate compounds. Do not show any (arrow pushing) mechanisms.

this problem is slightly tricky, substitution here is SN1, the choice between SN1 and SN2 in simpler cases is the usual one, you can't do SN2 on a tertiary carbon and you can't do SN1 on a primary carbon, secondary is always a bit ambiguous, as is allylic, because both SN2 and SN1 are favored at this positions, HOWEVER, this is a mechanism problem, and in this case I gave you the product and you can see that the substitution can't have been Sn2 because the -Br is not on the original carbon that had the leaving group, so in this case it had to be SN1

a)

Br MgBr OH

OH

Mg.THF 1.

2. H3O+

O

Na2Cr2O7/H2SO4/H2O

OBr2/hν

b)

20


c) OH

Br

MgBr

OH

O

Mg.THF

PBr3

PCC

1.

2. H3O+

O

H Ph

a)PCC/CH2Cl2

1. MeMgBr2. H3O+

OH

O

OH

b)MCPBA

1. PhMgBr2. H3O+

OPh

OH

Question 3. For each reaction.1) Provide the missing reagents/conditions or major organicproducts as appropriate2) Pay attention to stereochemistry including racemic mixtures unless specified

b)

a)

c)

1.MgBr (±)O

Ph

2. H3O+ OH

O

O

1. Excess CH3MgBr

2. H3O+

OH

OH

OH 1. PBr32. Mg.THF3. D2O

D

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