Chemistry 310M/318MDr. Brent Iverson2nd MidtermOctober 29, 2009

NAME (Print): _____________________________

SIGNATURE: _____________________________

Please Note: This test may be a bit long, but there is a reason. I would like to give you a lot of little questions, so you can find ones you can answer and show me what you know, rather than just a few questions that may be testing the one thing you forgot. I recommend you look the exam over and answer the questions you are sure of first, then go back and try to figure out the rest. Also make sure to look at the point totals on the questions as a guide to help budget your time.

Note: You must have your answers written in pen if you want a regrade!!!!

Please print the first three letters of your last name in the three boxes

10

9

8

7

6

5

4

3

2

(20)

(24)

(22)

(16)

(17)

(24)

(36)

(16)

(20)

(19)

(15)

(24)

(13)

(24)

(12)

(302)

11

1

Page Points

Total

TScore

HW

12

13

14

%

TotalGrade(HW score + Exam Grade)

15

Honor Code

The core values of the University of Texas at Austin are learning, discovery, freedom,

leadership, individual opportunity, and responsibility. Each member of the University is

expected to uphold these values through integrity, honesty, trust, fairness, and respect

toward peers and community.

(Your signature)

CH3CH2-H

R2C CH

H

H-N(i-C3H7)2

RC C H

COR'

O

RCH2

CR'

O

RCH2

CH

O

RCH2

CCl

O

RCH2

RCH2OH

HOH

ROC

O

COR'

O

CH2

RC

O

COR'

O

CH2

RC

O

CR'

O

CH2

H4N

CO-H

O

CH3

RCH2OH2

H3O

H-Cl

10

51

-7

Compound pKa

4.8

15.7

16

18-20

11

23-25

18-20

13

15-19

40

Acetic acid

!-Dicarbonyls

!-Ketoesters

!-Diesters

Water

Alcohols

Acid chlorides

Aldehydes

Ketones

Esters

LDA

Alkanes

Terminal alkynes 25

Terminal alkenes 44

9.2Ammonium ion

Hydronium ion

Hydrochloric acid

Protonated alcohol -2

-1.7

H3N 10.8Ethyl ammonium ion

CH2CH3

Pg 1 _____________(20)

1. (5 pts) What is the most important question in organic chemistry?

Signature_________________________

2. (10 pts) Write an acceptable IUPAC name for the following two molecules. Where appropriate, use E and Z or R and S.

Where are the electrons?

1

2

34

56

78

1

23

4

5

67

8910

3. (5 pts) Draw the structure that corresponds to the following name:

(3E, 5S, 6E, 8R)-4,5-diisopropyl-3,6,7,8-tetramethyl-1,3,6-decatriene

(3E,5E,7E)-5-isopropyl-2,3,4,8,9-pentamethyl-6-propyl-1,3,5,7-decatetraene

(3E,5E,7E)-2,3,4,8,9-pentamethyl-5-(1-methylethyl)-6-propyl-1,3,5,7-decatetraene

910

(3E, 5S, 6E, 8R)-3,6,7,8-tetramethyl-4,5-di-(1-methylethyl)-1,3,6-decatriene

(3E,5S,6R,7E)-2,3,4,5,6-pentamethyl-1,3,7-decatriene

1

23

45

67

89

10

This will not be graded

Pg 2 _____________(24)Signature_________________________

5. (10 pts) Amides are best represented as the hybrid of three contributing structures. Draw the second and third important contributing structures in the spaces provided, including all lone pairs and formal charges. For the two structures on the left in each problem, use arrows to indicate the movement of electrons to give the structures you drew. There is no need to draw any circles around any of these contributing strucures. You might want to read these directions again to make sure you know what we want

C

H

H

H

C

O

N

H

H C

H

H

H

C

O

N

H

H

C

H

H

H

C

O

N

H

H

6. For the following carbocation: A) State the hybridization state of the indicated atom in the square box provided. In the rectangular boxes, describe the bonds indicated by the arrows in terms of overlap between hybrid orbitals (the valence bond approach). For example, answers might be or!Csp3-Csp3 "C2p-C2pNote that this part of the question is NOT about hyperconjugation. We just want a valence bond description of the bonding in a carbocation structure.

C

C

CH

C

H

H

H

H

H

H

HH

!Csp2-Csp3sp2

!Csp3-Csp3

!Csp2-H1s(2 pts. each)

.

B) (6 pts) This part refers to hyperconjugation. On the structure, circle all of the sigma bonds that can take part in hyperconjugation with the carbocation.

NOTICE THIS

Pg 3 _____________(22)Signature_________________________

7. A) (8 pts) Complete the following structure of the artificial sweetener NutrasweetTM at pH 3.0,

the pH of soft drinks like Diet CokeTM. By adding appropriate numbers of lone pair electrons, H

atoms, and formal charges to the atoms in the boxes. (You do not have to add anything such as

H atoms to atoms not drawn in the boxes.) This problem is testing your understanding of the

relationship of protonation state to pH to pKa values for certain functional groups we have

discussed. Next, in the space provided, write the overall charge on each structure at the indicated

pH. For your reference, here are the relavant pKa values:

B) (1 pt. each) On the above structure, put an asterisk next to each chiral center.

C) (3 pt) Given the number of chiral centers you identified, how many total stereoisomers are

theoretically possible for NutrasweetTM?

22 = 4

D) (3 pt) What is the configuration at all the chiral centers in the molecule, R or S?

NNH

OCH3

O

O

O

O

NutrasweetTM at pH 3.0

Total charge at pH 3.0 ______+1*

*

H3C OH

O

H3C NH3

pKa = 10.64pKa = 4.76

H

HH

H

G) (3 pt) At pH of 7.0, what is the total charge on the NutrasweetTM molecule?

0

S

E) (2 pt) NutrasweetTM is made of the amino acids Aspartic Acid and Phenylalanine. Are the amino acids

in Nutrasweet the same configuration as the configuration of the amino acids most commonly found in all

living oganisms on this planet? Yes

F) (2 pt) Would you expect the enantiomer or any of the diasterereomers of NutrasweetTM to taste sweet

to humans?

No

Signature__________________________ pg 4 ________ (16)

8. (4 or 6 pts each) Label each chiral center as "R" or "S" and on the line provided state whether the pair of molecules represent two enantiomers, two diastereomers, or the same compound. Draw a circle around any meso compound.

A. Relationship:

Enantiomers

B.Diastereomers

C.

S

Diastereomers

OH

OH OH

HO H

R

S

OH

OHO H

HO H

S

HO

O

HO

O

Meso

Did you remember to circle any meso compounds?

S

OH

OHO H

HO H

R

OH

OH OH

H OH

R

HO

O

HO

O

S

CH3

CH3

Br

Br

CH3

Br

Br

CH3

S

S

S

RMeso

Signature_________________________ Pg 5 _____________(17)

9. (6 pts) For each acid-base reaction, circle the side of the equation that predominates at equilibrium. In each case identify the stronger and weaker acids by comparing relative

stabilities of the anions which are the conjugate bases of the two acids. Equilibrium favors formation of the weaker acid. You will notice this means you circled the side with the more stable anion.

CC

O

HH

H

H

C

H

H C

H

H

H

+CC

O

H

H

H

C

H

H C

H

H

H

+ H

CCH H CN+ CCH CN H+

S

O

O

H3C CH3+ S

O

O

H2C CH3+

H H H

pKa = 20pKa = 23

C C

CH3

HH

H3CC C

H

HH

H

C C

H

CH3H

H3C

C H

H3C

H3C

C H

H

F3CC CH3

H3C

H3C

C H

H

H3C

10. (11 pts. total) Rank the following species in terms of the stated property from 1 to 4 (or 3) as described, with intermediate numbers to rank the species of intermediate stability activity. Please make sure you know what we want, as you will get no credit if you get the numbers backwards!

Stability of alkene: Place a 1 under the most stable (i.e. least reactive) and a 4 under the least stable (i.e. most reactive)

Stability of carbocations: Place a 1 under the most stable carbocation and a 4 under the least stable carbocation.

C C

CH3

CH3H3C

H3C

3 (cis) 1 4 2 (trans)

1243

Relative Acidity: Place a 1 under the most acidic molecule and a 3 under the least acidic molecule.

23 1

F C

F

F

C

O

O

H

C C

H

H

C

O

O

H

C C

H

H

C

O

O

H

F

F

F

H

H

C

F

F

F

CC

H

H

H

H3C

H Br

CC

H

H

H

H3C

Br Br

CC

H

H

H

H3C

B

H

H H

CH

H3C

C

H

H

H

CH

H3C

C H

H

Br

C

H

C

B

H

H

H

H

H3C

H

Br

Br

11. (6 pts each) For each set of reagents, draw the important intermediate or transition state that we discussed in lecture in the box provided. You must show all lone pairs and formal charges on the structures you draw!! Draw all species produced in this step of the mechanism Next, draw arrows on the starting materials to indicate electron flow to generate the intermediate or transition state that you have drawn. If the intermediate or transition state is chiral, you only need to draw one of the enantiomers, not both. Please read these directions again to make sure you know what we want. Note that we are only interested in the first step of the mechanism here, not the whole mechanism!

Signature_________________________ Pg 6 _____________(24)

A.

+

Intermediate

+

B.

+

Intermediate

+

D. For this one used dotted lines (•••••) to indicate bonds being made or broken in the structure you draw.

+

Transition state

C.

Intermediate

CC

H

H

H

H3C

Hg OAc

A.

+ CH

H3C

C H

H

Hg

OAc

Signature ______________________________ Pg. 7 ______ (36)

12. (24 pts.) Read these directions carefully. Read these directions carefully. (It was worth repeating) For the reaction of an alkene with water and a small amount of sulfuric acid shown below, fill in the details of the mechanism. Draw the appropriate chemical structures and use an arrow to show how pairs of electrons are moved to make and break bonds during the reaction. For this question, you must draw all molecules produced in each step (yes, these equations need to be balanced!). Finally, fill in the boxes adjacent to the arrows with the type of step involved, such as "Make a bond" or Take a proton away". MAKE SURE TO NOTICE THE QUESTIONS AT THE BOTTOM. If an intermediate or product is chiral, you only need to draw one enantiomer for this problem.

(4 pts) During the reaction described by the above mechanism, say what happens to the pH of the

solution _________________________________________________________________________________The pH stays the same because just as much acid is made as is used.

(4 pts) Is this reaction catalytic in acid? ____________________________________________________Yes

Products

S

O

O

OO

H

H H

O H

+

H

C

C

C

C

H

C

H

H

H

O HH

S

O

O

OO

H+

H

O HH

O HH

O HH

H

H

H

H

H

H

H

C

C

C

C

H

C

H

H

H

H

H

H

H

H

H

O HH

CC

O

C

H

HH

H H

H

H

H C

H

C

H

H

H

HCC

O

C

H

HH

H

H

H

H C

H

C

H

H

H

H

H

O HH

Electrophilic addition/add a

proton

Make a bond between a

nucleophille and electrophile

Take a proton away

(4 pts) One of the above steps involves making a bond between a nucleophile and electrophile. Draw a circle areound the Nuclophile in this step.

Nucleophile

12. A. (4 pts) For the reaction mechanism you drew on the previous page, draw a circle around the energy diagram that best describes your mechanism.

Signature ______________________________ Pg. 8______ (14)

Reaction Coordinate

PotentialEnergy

Reaction Coordinate

PotentialEnergy

Reaction Coordinate

PotentialEnergy

Reaction Coordinate

PotentialEnergy

B. (4 pts) Now draw an X through the energy diagram that best describes the reaction of an alkene with BH3, BEFORE the chemist opens the flask and adds H2O2/ HO-

X

C. (2 pts each) For the following, circle the capitalized word that best completes the statement.

For a reaction that has a favorable motive (thermodynamic driving force) as written, the products are LOWER or HIGHER in energy than the starting materials.

A reaction that has greater opportunity (occurs faster) has a LOWER or HIGHER activation energy.

A nucleophile will serve as an ELECTRON SOURCE or ELECTRON SINK for an arrow that indicates the making of a new bond.

An electrophile will serve as an ELECTRON SOURCE or ELECTRON SINK for an arrow that indicates the making of a new bond.

Signature_________________________ Pg 9 _____________(20)

13. The following molecule undergoes rearrangment. Draw the first carbocation intermediate in the first box, then the rearranged carbocation intermediate in the second. Include all lone pairs, formal charges, and arrows and draw the products of the reactions in the last box

A. (14 pts)

H Cl+

First carbocation intermediate

Rearranged carbocation intermediate

Rearrangement

Cl

Cl

2° carbocation

3° carbocation

C CH

HH

C

H

C

H

HH

H

C

H

C

H

HHH

H

C

H

C

H

HHH

Rearranged Product

Cl

Not chiral

B. (6 pts) For the following reactions, all of the observed products are shown. Deduce which reagents were used to produce these product mixtures from the starting alkene shown. Whrite those reagents above the arrows given in the boxes.

OH OHOH

Racemic

OH OH

Racemic

H2OH2SO4

1) Hg(OAC)2 H2O2) NaBH4

No rearrangement

Rearranged product indicating a carbocation

intermediate

Signature_________________________

14. (3-5 pts each) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-Markovnikov products) and please remember that you must draw the structures of ALL the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under all of the structures EVEN THOUGH YOU DREW ALL OF THE STRUCTURES.

Pg 10 __________(19)

B.CH3 CH3CHCH3

A. HBr

1. Hg(OAc)2 H2O

2. NaBH4

OH

(not chiral)

CH3 CH3CHCH3

Br

(not chiral)

C.CH3

1. BH3

2. H2O2 / HO(not chiral)

CH3CH2CH2OH

D.CH3

Racemic

Br2

Br

Br

Br

Br

E.CH3

Racemic

Cl2Cl

OH

Cl

OHH2O

Signature_________________________

14. (cont.) (3-5 pts each) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-Markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under all of the structures EVEN THOUGH YOU DREW ALL OF THE STRUCTURES.

Pg 11 __________(15)

G.

H.

Racemic Mixture

Racemic Mixture

F.

Racemic Mixture

CH3

Cl

H

Cl

Cl

CH3

Cl

H

Cl2

H2O

H2SO4

OH OH

1. BH3

2. H2O2 / HO

OH OH

Signature_________________________

13. (4 or 6 pts each) The following problems are a new format. We turn the tables and give you the product. In the box provided, draw the starting material required to make that product AS THE PREDOMINANT ONE(S) using the given reagents. When more than one starting material would work, you must draw both.

Pg 12 __________(24)

A.

BrBr

H3CH2C

H3C

H

H

Br2

(Racemic Mixture)

BrBr

H3CH2CH

HH3CB.

C.

1) BH3

2) H2O2 / HO

or

12. (cont.) (10 pts) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-Markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under all of the structures EVEN THOUGH YOU DREW ALL OF THE STRUCTURES.

G.

H2SO4 (catalytic)

H2O

CH3

OH

Not Chiral

HBr

(Racemic Mixture)

CH3

H

CH3

OH

H

CH3

OH

CH3

CH3

H

OH

CH3

H

CH3

Racemic

CH3

Br

OH OH

Signature_________________________

14. (13 pts total) Organic chemistry is a very creative science because there are so many different reactions known that often we are only limited by our imaginations. For example, the same starting alkene can be converte to the different products listed. Deduce the identity of the starting alkene, and write its structure in the box labeled "Starting Alkene". Fill in the boxes containing arrows with the reagents required to produce the given products.

Pg 13 __________(13)

1) BH3

2) H2O2 / HO

HI

Cl2

OH

Racemic

Cl Cl

Cl Cl

I II

Racemic

Starting Alkene

HBr

HBr

CH3

HBr

H3C Br

H-Br

Br CH3

CH3

Br

CH3

H-Br

CH3

Br

CH3

Br

CH3

Br

H3C Br

Signature_________________________ Pg 14__________(24)

Racemic

14. (6 pts) Assuming no rearrangements, draw the three different alkenes that can give rise to the indicated racemic mixture of products with reacted with HBr.

or

or

14. (18 pts) For the following reaction, draw all possible products including the different regioisomers and stereoisomers. For this part, assume no rearrangement takes place.

A) No rearrangement

D) Now draw any additional product(s) you would see upon rearrangement of the intermediate carbocation.

(not chiral)

B) In your answer to part A), did you draw any pairs of enantiomers? _________No

C) Is your answer to part A) a racemic mixture? _________No

Rearranged product(s)

Signature_________________________

15. (12 pts total) The following reaction will generate a number of products. Assume there is enough Br2 so that both pi bonds react completely. Note you do not have to draw the products here, we just want you to answer the questions based on the chemistry intuition you have gained so far.

Pg 15 __________(12)

excess Br2

A. How many chiral centers will be created in this reaction? ______

B. How many total stereoisomers are possible given this number of new chiral centers created? _____

C. How many stereoisomers will be produced in this reaction? ______

D. In no more than one or two sentences, explain your answer to part C. above.

4

16

4

The anti addition stereochemistry requirement of this reaction means that at each pi bond only two different stereoisomers will be produced. Because there are two pi bonds, the total number of stereoisomers observed will be 2 x 2 = 4 out of the 16 possible stereoisomers.

Br

Br Br

Br

Br

Br

Br

Br

Br

Br

Br

Br

Br

Br

Br

Br

You did not have to draw them, but these are the four stereoisomers produced for your reference.