CHEM 244 - Organic Chemistry II – Spring 2021

Worksheet #6: Videos 18-1, 19-1 & 19-2

Target date for completion of Worksheet #6: April 26

The Last CHEM 244 Worksheet!!!

Complete the following worksheet by the target date by (1) working with a group of students during class time, and (2)

working on your own outside of class. You can use the CHEM 244 course web page, and any resource available to you,

but I strongly discourage the use of Wikipedia and online homework sites (like Chegg). During class time you will get

help from the course instructor, the Peer Leaders, and other students.

The purpose of this worksheet is to apply the principles you learned in the corresponding lecture videos. I will NOT

collect this worksheet. I advise you to print this worksheet and answer the questions in the space provided. I encourage

you to save this worksheet in your course notebook for study purposes, and I will post an answer key.

~~There are extra practice problems at the end of this worksheet~~

Dates CHEM 244 Videos Classwork Class Project

April 21 (W) 18-1 Carbanions (skip video 18-2) WS-6, problems 1-4 50-word description, abstract, PP format

April 23 (F) 19-1 (Aldol condensation – start at 7m11s) WS-6, problems 5-7 Deadline to upload presentations!

April 26 (M) 19-2 Michael Addition (last video!) WS-6, problems 8-10 StARS Symposium: April 26 – May 10

April 28 (W) Group Quiz #6 StARS Symposium: April 26 – May 10

April 30 (F) Exam #4 (WS 6) StARS Symposium: April 26 – May 10

May 3 (M) Last class – Attendance Required Course and peer evaluation; Alexis leads focus group discussion

May 4 (T) Reading Day – Exam #4 returned Students decide whether to take Make-up Exam

All office hours during Final Exams will be by appointment for Dr. Brush and Peer Leaders

May 5 (W) Last day to sign-up for make-up exam

May 7 (F) OPTIONAL Make-up: 8:00 am (open to students in all sections)

May 10 (M) OPTIONAL Make-up: 8:00 am (open to students in all sections)

Class Project Information: Your Group Project counts 100 points toward your final grade (10%).

• (20 Points - individual): Group work on the Project (Peer Evaluation survey)

• (30 Points - group): Completion of all 5 objectives in your MS Teams group notebook

• (10 Points – individual): Individual reflection (objective 5)

• (20 Points - group): Completed group power point in MS Teams

• (20 Points - group): Power point successfully uploaded by the April 23 deadline

• You will have two options for submitting your power point:

o PDF Slideshow (no narration) – RECOMMENDED!

o Narrated Slideshow (slides with voice recording)

• One person in your group will volunteer to upload the presentation as part of the 15 courses conducting project

work on the UN SDGs and environmental justice. I will send the upload instructions.

• The StARS symposium will run virtually from April 26 – May 10. Be sure to log-in to the symposium so you can

check your presentation for questions and comments. Also, be sure to visit other presentations in the UN

SDG/environmental justice block to see how students in other courses and disciplines approached this project!

PLEASE READ: OPTIONAL Make-up Exam Information!

• Exam #4 will be returned to you by Tuesday, May 4. On the first page of that exam you will see your Final Grade,

and all information used in calculating your Final Grade. You can then decide whether you want to take the

Make-up Exam to try and improve your Final Grade.

• If you decide to take the Make-up Exam, you must notify me no later than Wednesday, May 5 at 5 pm.

• If you do not sign-up for the Make-up Exam, I will assume that you are satisfied with the Final Grade written on

Exam #4.

• Your Make-up Exam grade will replace your lowest grade from Exams 1-4.

• The Make-up Exam will follow this format:

o Same format as Exams 1-4: 5-6 pages, 100 points, same amount of time as the other exams (80 minutes)

o PLEASE NOTE: Once I email the make-up exam to you it must be completed. Otherwise, you forfeit

the make-up.

o The Make-up Exam will cover material from Exams 3 and 4 only.

o You have the following two options as to when you can take the Make-up Exam:

▪ Friday, May 7 at 8:00 am (I will email the exam at 8:00 am and it must be returned by 9:20 am)

▪ Monday, May 10 at 8:00 am (I will email the exam at 8:00 am and it must be returned by 9:20 am)

Video 18-1 Carbanions

(1) Carbanions and Resonance

Structures. Compound A is

proposed to form two possible

carbanions, B and C. Carbanion C

is more stable as it has more

resonance structures to delocalize

(and stabilize) the carbanion.

REMEMBER: Carbanions will form if there is an acidic H on a sp3 carbon that is adjacent to or conjugated with a

carbonyl.

Complete the following Resonance Structures for carbanions B and C by adding the appropriate charges, and complete

the [Hybrid Resonance Structure] for each by adding the partial double bonds and partial charges:

CIRCLE the enolate ion for B and C.

(2) Carbanions. In each of the following compounds, CIRCLE any carbon atom that will form a stable carbanion when

an acidic proton is removed by a strong base. HINT: You are looking for an acidic H on a sp3 carbon that is adjacent to or

conjugated with a carbonyl.

(3) H-to-D exchange. In each of the following compounds, CIRCLE any CH’s that are likely to undergo base-catalyzed

exchange of H for D. Remember, you are looking for any carbon that will form a stable carbanion when an acidic proton

is removed by a strong base. HINT: You are looking for ALL acidic H’s on a sp3 carbon that are adjacent to or

conjugated with a carbonyl.

(4) Mechanisms: Base-catalyzed H-to-D exchange.

The reaction drawn at the right shows a base-

catalyzed H-to-D exchange.

(a) From this list of structures, drag the appropriate carbanion, enolate and enol into the correct boxes below to complete

the Tautomerization Process for this racemization:

(b) Substituent Effects. If the aldehyde reactant in the exchange reaction were

replaced with the molecule drawn at the right, would you expect the rate of H-to-D

exchange to increase, decrease or stay the same. Explain your answer.

ANSWER: The rate will increase as the substituent is an EWG. There are several reasons:

1) The EWG will increase the acidity of the acidic proton by weakening the C-H bond.

2) The EWG will stabilize the carbanion (conjugate base) through delocalization of charge.

3) The position of the EWG will also allow for additional resonance structures to stabilize the carbanion.

Video 19-1 Aldol Condensation

(5) Aldol Condensation Reactions. Complete the reactions shown below by drawing the structure of the organic

products, or the appropriate structure of the reactants.

***The “dots” have been added as a guide to the ring closing.

(6) Mechanisms – Aldol Condensation (5 steps). The PARTIAL mechanism (series of balanced chemical equations)

has been done for you. All you need to do is add the curved arrows and proper charges.

(7) Structure Identification. Unknown Compounds A and B contain only C, H & O atoms. These two unknowns are

believed to have a combination of one or more of the following functional groups: alcohol, aldehyde, ketone, carboxylic

acid, ester, benzene ring. General Information:

I. The IR spectrum for Compound A revealed the following characteristics: Broad IR band at 3200-3600 cm-1, and weak

jaggered bands between 1800-2000 cm-1.

II. The IR spectrum for Compound B has a broad band at 2800-3300 cm-1 and a sharp band at 1700 cm-1. Compound B is

insoluble in water, but soluble in dilute aqueous base.

III. When Compounds A & B were reacted with H2SO4 catalyst, a new Compound C was obtained:

The IR spectrum for Compound C revealed the following characteristics: A sharp band at 1700 cm-1, and a series of

weak, jaggered bands between 1800 – 2000 cm-1.

(a) Based on ALL the information given above, identify all functional groups present in Compounds A, B and C. Circle

your choices for each compound. You do not need to explain your answers.

Compound A: alcohol aldehyde ketone carboxylic acid ester benzene ring

Compound B: alcohol aldehyde ketone carboxylic acid ester benzene ring

Compound C: alcohol aldehyde ketone carboxylic acid ester benzene ring

(b) The 1H NMR data for Compounds A and B are summarized in the Tables below. Draw a possible structural fragment

for each signal.

COMPOUND A (*After adding D2O, this signal disappeared) H nuclei (a) (b) (c) (d) (e)*

Chemical shift 7.2 ppm 2.9 ppm 2.4 ppm 1.9 ppm 3.4 ppm*

# of protons 5H 1H 2H 3H 1H

Splitting ------- m d d s

COMPOUND B (*After adding D2O, this signal disappeared)

H nuclei (f)* (g) (h) (i)

Chemical shift 12.2 ppm 2.9 ppm 2.4 ppm 1.9 ppm

# of protons 1H 2H 1H 6H

Splitting s d m d

COMPOUND A FRAGMENTS: (a) (b) (c) (d) (e)

COMPOUND B FRAGMENTS:

(f) (g) (h) (i)

(c) Based on the NMR data, propose structures for compounds A and B, and finally, C.

(d) Complete the table below for what you expect in the 13C NMR for the structure of Compound C that you drew above.

Total aromatic 13C signals

Total 13C signals

Total 13C signals that would appear as singlets

Total 13C signals that would appear as doublets

Total 13C signals that would appear as triplets

Total 13C signals that would appear as quartets

Video 19-2 Michael Addition Reaction

(8) Michael Addition Reactions. Complete the reactions shown below by drawing the structure of the organic products,

or the appropriate structure of the reactants.

***The “dots” have been added as a guide to the ring closing.

(9) Mechanisms: Michael Addition Reaction (2 steps). The PARTIAL mechanism (series of balanced chemical

equations) has been done for you. All you need to do is add the curved arrows and proper charges.

(10) Mechanisms – Intramolecular Michael Addition (3 steps). The PARTIAL mechanism (series of balanced

chemical equations) has been done for you. All you need to do is add the curved arrows and proper charges.

***The “dots” have been added as a guide to the ring closing.

~~~ Extra practice problems for Worksheet #6 ~~~

(11) Carbanions. Which of the following compounds are likely to undergo racemization in the presence of NaOH(aq)?

Circle your choice(s).

REMEMBER: Carbanions will form if there is an acidic H on a sp3 carbon that is adjacent to or conjugated with a

carbonyl.

(12) Tautomerization. When the compound drawn below reacts with base, two, different carbanions are formed.

(a) Complete the boxes below by drawing the

structures of the two carbanions, and the

corresponding enolates and enols.

(b) Which carbanion is more stable? Explain your choice.

ANSWER: As drawn above, carbanion #1 is more stable as it is closer to the EWG (fluorine) which can help

delocalize the negative charge of the carbanion.

(c) Substituent Effects. If the ketone reactant were replaced with the molecule drawn

at the right, would you expect the rate of carbanion formation to increase, decrease

or stay the same. Explain your answer.

ANSWER: The “O” is a strong EDG. This will make the C-H bond stronger (less likely to be removed by a base),

and the EDG will destabilize the carbanion by making it stronger.

(13) Mechanisms: Base-Catalyzed Racemization.

The reaction drawn at the right shows a base-

catalyzed racemization.

(a) Explain why this compound is able to undergo racemization.

ANSWER: Racemization requires the formation of a carbanion. A carbanion will form as there is an acidic H on a

sp3 carbon that is adjacent to (conjugated) with a carbonyl.

(b) From this list of structures, drag the appropriate carbanion, enolate and enol into the correct boxes below to complete

the Tautomerization Process for this racemization:

(14) Aldol and Michael Addition Reactions. Complete the reactions shown below by drawing the structure of the

organic products, or the appropriate structure of the reactants.

***The “dots” have been added as a guide to the ring closing.

***The “dots” have been added as a guide to the ring closing.

(15) Mechanisms - Intramolecular Aldol Condensation (5 steps). The PARTIAL mechanism (series of balanced

chemical equations) has been done for you. All you need to do is add the curved arrows and proper charges.

***The “dots” have been added as a guide to the ring closing.

(16) Mechanisms - Michael Addition Reaction (3 steps). The PARTIAL mechanism (series of balanced chemical

equations) has been done for you. All you need to do is add the curved arrows and proper charges.