[PDF] Fall 03 Exam 3 PDF

[PDF] Bent bonds and the antiperiplanar hypothesis - Université Laval

21 juil 2016 · The bent bond/antiperiplanar (BBA) hypothesis has been applied to the state geometry, regio- and stereoselectivity of a wide range of

[PDF] Bent Bonds (?) and the Antiperiplanar Hypothesis The Chemistry of

1 mai 2018 · geometry, the cyclization through 1b must be a conrotatory process that can only form the highly strained trans-BOT,

11-11-19pdf

E2 reaction to take lace on cyclic molecule (cyclohexanes) the X and H must both be axial an a antipt antiperiplanar geometry required

[PDF] PERSPECTIVE

Bent bonds, the antiperiplanar hypothesis and the theory of resonance A accounts for the preferred antiperiplanar geometry of the E2 elimination

[PDF] Stereoselectivity in E1 (E or Z)

E2 occurs via anti-periplanar transition state when possible because If only one proton can be eliminated then geometry of alkene

[PDF] Elimination Reactions

E2 elimination occurs most often in the anti periplanar geometry The stereochemical requirement of an anti periplanar geometry in an E2 reaction has

[PDF] Fall 03 Exam 3

A ) E2 reactions involve an antiperiplanar arrangement of a hydrogen atom and the requirement for an anti-periplanar transition state geometry in an E2

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14543_6Fl03Exam3Ques.pdf 10 9 8 7 6 5 4 3 2 (10) (16) (22) (18) (27) (21) (21) (23) (15) (20) (15) (208) 11 Total T Score 1

Page Points

Signature_________________________

Pg 1 _____________(10)

1. (10 pts) Circle all the True statements. (Do not circle any false statements) You may notice that

many of these resemble rules of the day!

A.) E2 reactions involve an antiperiplanar arrangement of a hydrogen atom and leaving group in the key

intermediate. B.) E2 reactions involve an antiperiplanar arrangement of a hydrogen atom and leaving group in the transition state.

C.) An S

2 reaction on a primary alkyl halide has a lower overall energy barrier compared to a S

N 1 reaction on a primary alkyl halide, because in an S N

2 reaction the nucleophile actually assists in breaking

the carbon leaving group bond, while in an S N

1 reaction the carbon leaving group bond must break on its

own.

D.) For cyclohexyl halides, the requirement for an anti-periplanar transition state geometry in an E2

reaction means that the halide leaving group must be axial, never equatorial. E.) Alkenes are more stable with more alkyl groups attached. F.) Polar protic solvents cannot take part in hydrogen bonding. G.) H-bonding due to the OH group makes alcohols "sticky" so they have high boiling points and alcohols with three or less carbons dissolve completely in water.

H.) The OH group is not a leaving group, but several reactions involve the conversion of the OH

group into a good leaving group , followed by a substitution or elimination reaction.

I.) Primary and secondary alcohols react with PBr

3 and SOCl 2 to give alkyl bromides and alkyl chlorides, respectively, via a mechanism involving a carbocation intermediate. J.) Alcohol dehydration is just the functional reverse of acid-catalyzed alkene hydration becuase the process is actually an equilibrium, the position of which depends on the reaction conditions. CH 3 CCH 3 CH 3 C H CH 3 H H CH H C H CH 3 CH 3 Br Br Br Br

Signature_________________________

relative rank: CH 4 CH 2 CH 3

Pg 2 _____________(16)

CH 3

2. (4 pts total) For the following compounds, rank them in order of most to least reactive with Br

radicals in a free radical halogenation reaction, with a 1 under the most reactive and a 4 under the

least reactive. relative reactivity: H 2 C CH CH 3 C CH 3 H 3 C CH 3 CH 3

3. (4 pts total) For the following compounds, rank them in order of reaction rate from fastest to slowest

with a nucleophile in an S N

2 reaction, with a 1 under the fastest and a 4 under the slowest.

relative stability:

4. (4 pts total) For the following compounds, rank them in order of most to least stable alkene, with a 1

under the most stable and a 4 under the least stable. H 2 CCH 2 relative rank:

5. (4 pts total) For the following compounds, rank them in order of highest to lowest boiling point, with

a 1 under the molecule with the highest boiling point and a 4 under the molecule with the lowest boiling point. ClOH HO OH Are you sure you ranked them in the correct order according to the directions????

Signature_________________________

Pg 3 _____________(22)

Br H Cl H Cl Cl H H Br H Br H Cl Br H H HO F H F OH H HO F F H OH H OH C CH 2 CH 3 H 3 C H OH C CH 2 CH 3 H 2 C H H 3 C

6. (9 pts total) You will recognize this from the last test. We felt that many of you needed more practice

wity chirality so here it is again. Of the molecules shown below, circle the ones that are optically active,

that is the ones for which a sample would rotate the plane of plane polarized light. In other words, circle

the molecules that are chiral. By the way, just to keep you honest we moved the molecules around so do

not try to remember the location of the circled answers from last test. Br H

6. (13 pts total) For the following, fill in each blank with S

N 1, S N

2, E1, or E2 in order to best complete

the following statements. A. Scrambled stereochemistry results from an __________ reaction at a stereocenter. B. _________ reactions always result in inversion of stereochemistry

C. Primary alcohols react with concentrated H

2 SO 4 by protonation followed by an ________ reaction to yield an alkene. D. _________ and __________ involve the formation of carbocation intermediates. E. The reaction rate of _________ and __________ reactions can be altered by changing the concentration of the nucleophile/base or the alkyl halide. F. The reaction rate of _________ and __________ reactions can only be altered by changing the concentration of the alkyl halide. G. Polar protic solvents accelerate _________ and __________ reactions. H. Zaitzev's rule applies to _________ and __________ reactions.

Signature_________________________

Pg 4 _____________(18)

7. (8 pts total) We have encountered some resonance stabilized intermediates in class recently. The

allyl radical is a good example. In the spaces provided, draw two resonance contributing structures of

the radical intermediate formed when cyclohexene reacts with a bromine radical. Use arrows to indicate

the flow of all electrons. H H HH H H H H HH Br

8. (10 pts total) S

2 and E2 reactions each occur via a key transition state. In the boxes provided, draw

the transition states for the given S N

2 and E2 reactions. No need to draw any arrows here, but use

dashed lines to indicate bonds that are being broken or formed in the transition state. Make sure to show

all lone pairs. Notice that we gave you a lot of room so please make your drawings clear for us to grade.

CBr H 3 C H 3 CH 2 C H NC+ CC H 3 C H 3 CH 2 C H HO+ Br CH 3 H +

9. (5 or 7 pts each) The following reactions all involve substitution and/or elimination. Fill in the box

above the arrow with the mechanism that will be followed (S N

2, E2, etc.). Then draw only the

predominant product or products and please remember that you must draw the correct stereoisomers. When a scrambled mixture is formed, you must write "scrambled" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. For S N

1/E1 reactions you must

draw both types of products. +

Signature_________________________

Pg 5__________(27)

A. E. B. D. + CH 3 OH

Na N

3 CH 3 CH 2

O Na

Na SH

I Br CH 3 H Br H

Na CN

+ H 3 CH Br H H 3 CH Br CH 3 heat

All Products

STEP 1

STEP 2

10. (21 pts.) Read these directions carefully. Read these directions carefully. (It was worth repeating)

For the reaction shown below, fill in the details of the mechanism. Draw the appropriate chemical structures and use arrows to show how pairs of electrons are moved to make and break

bonds during the reaction of the indicated alcohol with H-Br. Hint: There is a rearrangement step in

this reaction. Make sure to draw all lone pairs of electrons, all formal charges, and all products (including stereoisomers) produced along the way.

Signature ______________________________ Pg. 6 ______ (21)

.. O H .. HBr .. .. ..

Redraw Intermediate AIntermediate B

STEP 3

Redraw Intermediate BIntermediate C

STEP 4

Redraw Intermediate C

2° alcohol H 3 C H

Intermediate A

Signature ______________________________ Pg. 7 ______ (21)

Br Br H Br Br H CH 3 H H 3 CH Br H H CH 3 HCH 3 Br Br CBr H H H

11. (12 pts.) Draw the predominant product that results from the following E2 elimination reactions.

We gave you a little extra room to work the harder ones.

B. (Challenge)

CH 3 HI H H 3 C H 3 C

C. (Challenge)

Br H H CH 2 CH 3 H 3 CH I A. OtBuK Na OtBuK

10. (9 pts.) For the following, circle all of the molecules that will primarily react via an E2 mechanism

when treated with Na OCH 2 CH 3 . OCH 2 CH 3 Br CH 3 H CH 3 HCH 3

12. (3-5 pts each) Fill in the box with the product or products that are missing from the following

chemical reaction equations. Draw only the predominant product or products and please remember that you must draw the structures of all the predominant product stereoisomers. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. If a scrambled mixture is produced, you need to write "scrambled".

Signature_________________________

Pg 8__________(23)

CH 3 A. OH B. hν C. hν H OH D. PBr 3 H-Br

This rearranges!

H 2 SO 4 CH 3 SO 2 Cl H 2 CrO 4 Br 2 Br 2

13. (3 pts each) Fill in the box with the product, starting material or reagents that are missing from the

following chemical reaction equations. Draw only the predominant product or products and please remember that you must draw the structures of all the predominant product stereoisomers. When a racemic mixture is formed, you must write "racemic" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. If a scrambled mixture is produced, you need to write "scrambled". You do not need to refer to the solvent unless it is one of the reagents.

Signature_________________________

Pg 9__________(15)

A. I H B. hν CH 3 Br C. PBr 3 D. OH H O

E. (Challenge!!!)

H 3 C H hν NBS CH 3 Br H Br 2

14. (4 pts each) This is similar, but not identical to the last one. Fill in the boxes with the product, starting

material or reagents that are missing from the following chemical reaction equations. Draw only the

predominant product or products and please remember that you must draw the structures of all the predominant product stereoisomers.

Signature_________________________

Pg 10__________(20)

hν

K OtBu

H OH A. B. HOH HSCH 3 Br 2

Na SCH

15. (15 pts) Definitely save this until the end!!! There are at least five different molecules that will react

with H-Br to give the indicated product as the predominant product. Draw them in the boxes provided.

Hint 1; At least two involve a rearrangement and Hint 2; Different stereoisomers are considered different molecules

Signature_________________________

Pg 11__________(15)

CH 3 Br H-Br H-Br H-Br H-Br H-Br

[PDF] Fall 03 Exam 3

Page Points

Signature_________________________

Pg 1 _____________(10)

1. (10 pts) Circle all the True statements. (Do not circle any false statements) You may notice that

C.) An S

2 reaction on a primary alkyl halide has a lower overall energy barrier compared to a S

2 reaction the nucleophile actually assists in breaking

1 reaction the carbon leaving group bond must break on its

I.) Primary and secondary alcohols react with PBr

Signature_________________________

Pg 2 _____________(16)

2. (4 pts total) For the following compounds, rank them in order of most to least reactive with Br

3. (4 pts total) For the following compounds, rank them in order of reaction rate from fastest to slowest

2 reaction, with a 1 under the fastest and a 4 under the slowest.

4. (4 pts total) For the following compounds, rank them in order of most to least stable alkene, with a 1

5. (4 pts total) For the following compounds, rank them in order of highest to lowest boiling point, with

Signature_________________________

Pg 3 _____________(22)

6. (9 pts total) You will recognize this from the last test. We felt that many of you needed more practice

6. (13 pts total) For the following, fill in each blank with S

2, E1, or E2 in order to best complete

C. Primary alcohols react with concentrated H

Signature_________________________

Pg 4 _____________(18)

7. (8 pts total) We have encountered some resonance stabilized intermediates in class recently. The

8. (10 pts total) S

2 and E2 reactions each occur via a key transition state. In the boxes provided, draw

2 and E2 reactions. No need to draw any arrows here, but use

9. (5 or 7 pts each) The following reactions all involve substitution and/or elimination. Fill in the box

2, E2, etc.). Then draw only the

1/E1 reactions you must

Signature_________________________

Pg 5__________(27)

Na N

O Na

Na SH

Na CN

All Products

STEP 1

STEP 2

10. (21 pts.) Read these directions carefully. Read these directions carefully. (It was worth repeating)

Redraw Intermediate AIntermediate B

STEP 3

Redraw Intermediate BIntermediate C

STEP 4

Redraw Intermediate C

Intermediate A

11. (12 pts.) Draw the predominant product that results from the following E2 elimination reactions.

B. (Challenge)

C. (Challenge)

10. (9 pts.) For the following, circle all of the molecules that will primarily react via an E2 mechanism

12. (3-5 pts each) Fill in the box with the product or products that are missing from the following

Signature_________________________

Pg 8__________(23)

This rearranges!

13. (3 pts each) Fill in the box with the product, starting material or reagents that are missing from the

Signature_________________________

Pg 9__________(15)

E. (Challenge!!!)

14. (4 pts each) This is similar, but not identical to the last one. Fill in the boxes with the product, starting

Signature_________________________

Pg 10__________(20)

K OtBu

Na SCH

15. (15 pts) Definitely save this until the end!!! There are at least five different molecules that will react

Signature_________________________

Pg 11__________(15)

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