Announcements (please read them carefully since you are going to held responsible)
1. Infrared assignment
The infrared assignment for this quarter is due by Friday, August 15, 2014 at 4:30 pm in YH 3077E. No late assignments will be accepted. If you are not at school on this day, you are welcome to drop off the assignment earlier (into the large grey mailbox outside the instructor's office in the office suite or the instructor directly). Do not slide it through under the instructor's office door and do not drop it off in the faculty mailbox either. Submission via email will not be accepted either.
2. Safety
a. Make sure to be careful when you handle glassware. This applies to its use during a reaction as well as the cleaning part. Broken glassware can cause very deep cuts, which have often to be stitched up (we had several cases of this over the years already). If chemicals get into the open wounds, the wounds have to be specially treated and the healing process usually takes longer than normal as well.
b. It has come to the attention of the instructor that students have been dumping acetone down the sink. This is entirely unacceptable. If a student will be caught doing this, s/he will receive an automatic zero for the entire lab meeting. Repeat offenders will be dismissed from the course on the account of being a safety risk. CAL OSHA will spell out very hefty fines for such violations because this is prohibited by California law!
c. The students are not allowed to use any reader in the lab. All information that is needed to carry out the experiment has to be included into the pre-lab. A student that uses the readers in the lab (for whatever reason) is deemed to be unfit for the lab and will receive a zero in-lab evaluation score for this lab meeting. The student will not be allowed to perform an experiment without a prelab!
d. Make sure to inform yourself about the hazards of the chemicals that you are using in the lab by reviewing the MSDS sheets for the chemicals used in the lab. It is your responsibilty to be informed about that for your own protection. Please keep in mind that you can also be tested about this knowledge by the TA, the instructor and any safety inspector i.e., departmental safety officer, EHS officer, CAL OSHA officer, reps from the City of Los Angeles, etc.
e. If you have to attend a different lab section, you will have to consult with the instructor. In the past, students attended a different lab section without permission, which poses a problem to everybody in the lab due to limited resources and safety issues (overcrowding of the lab, etc.). Failure to get permission from the instructor in the future will result in a 10-point penalty and automatic dismissal from the section.
f. The vacuum trap and the filter flask have to be clamped during the vacuum filtration.
3. Administrative Issues
a. It is important that the students leave the lab by 5:00 pm.
b. Each student has to submit the answers to his quizzes himself/herself. It is not acceptable that a fellow student does it under their name. This is considered cheating and will dealt with appropriately.
c. If you plan to work on the extra credit assignment, make sure to turn in your prelab to the instructor before you start the project. The latest day to turn in the prelab is August 22, 2014 at 4:30 pm. Don't forget to include the prelab questions and the PROPER infrared spectrum (with the identification of the key peaks). You will not be allowed to conduct the experiment before you turned in the prelab. No exceptions.
d. The extra credit experiment will be started during August 26 or August 27, 2014 during the student's regular lab meeting. The workup will probably take place one week later.
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Week 4 Problem Set - 30 BL (Turn in your computer assignment during meeting 5)
Part I: Phase Transfer Oxidation (due in prelab)
1. Please watch the following video (MP4-format) and read the appropriate chapter in the "Survival Kit Reader". Then take the quiz below.
Video: Extraction
Online Quiz: http://bacher.chem.ucla.edu/TakeQuiz/?id=c51ce410c124a10e0db5e4b97fc2af39
In order to take the quiz, you have to go through a UCLA ICP address. This means that you either have to use your Bruin-Online account or go through the VPN (Vitual Private Network, software can be found here: http://www.bol.ucla.edu/services/vpn/) to have this UCLA ICP address. If the video does not start automatically, you will have to download it first and then start it directly from Real Player or a similar program, etc.
To log in, use your last name and your student ID. If you are experiencing problems, contact the instructor via email and include your full name (indicated which one is your last name), your student ID, section and TA. (Hint: Think very careful about each response since many of the questions have more than one answer to them! Many students come up with the most obvious one and miss some of the details which leads to a zero score for the question!) Even though you can take the quiz until one hour prior to meeting 4 of your section, you should not delay taking it since there might be some problems with the server or the login. Also, there seem to be problems with MAC systems, Safari and Google Chrome Browser. The best is using IE 8.0 or Firefox. After you submit the answers, your score has to appear on your screen. If this does not happen, you will have to retake the quiz. (There will not be any possibility to retake the quiz weeks later since you are supposed to show preparedness at the point in time when you enter the lab!). The quiz is worth 10 points.
2. Referring to the phase transfer reaction carried out in the lab, answer the following questions.
a. What is the function of TBHS in this reaction?
b. Why is ethyl acetate used as the solvent in the reaction?
c. Why is it important that the reaction mixture is stirred vigorously?
d. Why is it important to observe "Rule 26"?
e. Why is it important that the organic layer dried thoroughly and concentrated before performing column chromatography?
f. What is used as stationary phase and mobile phase in the column chromatography step?
g. The student does not completely remove the ethyl acetate after the chromatography step. Which problem does this pose?
h. Using a non-polar column i.e., C18 in HPLC, what would be the elution sequence of the compounds?
PART II. (Molecular Modeling II)
This assignment is to be completed in the UCLA Science Learning Center computing labs during the lab period (or afterwards if you do not complete it in the allotted time). The assignment is due during meeting 5 and is worth 10 points.
Instructions:
- Build, minimize and save the structure. (don't forget to Minimize the structure after building it!!)
this is the minimize button. Always minimize your structure before leaving the building mode.
- click on
to enter View Mode
- Select Calculations from the Setup menu.
The following window should appear. Select the options shown.
Verify the Charge is Neutral and Multiplicity is Singlet. Click OK.
- Select Submit from Setup menu.
- When the calculation is completed you will be notified.
- Select Output from the Display menu.
Record the heat of formation value given
See these Helpful Hints for manipulating structures!
PART IIa. (Aldol Condensation, In-lab assignment)
|
1. Calculate the dipole moment and the energy for dihedral angles: 0, 20, 40, 60, 80, 100, 105, 110, 125, 140, 160, 180 |
Newman Projection of Benzil |
Instructions:
- click on Constrain Dihedral angle tool,
- select the atoms shown below in the specific sequence O..C..C..O. This will define two planes O1C1C2 and C1C2O2, which are going to be rotated towards each other in this part.
- Click on the lock tool,
, in the bottom right corner so that it looks like this,
- Set the dihedral angle to 0 and hit the ENTER key.
- click on the minimize tool,
, and wait for the operation to complete.
- click on the minimize tool,
- Select Calculations from the Setup menu. The following window should appear. Select the options shown.
- Make sure the
are checked!
- Click OK to close the window.
- Select Submit from Setup menu. When the calculation is completed you will be notified.
- Under the Display menu, select Properties.
- A window should appear (the values in this example should differ from yours). If there are no values in the window then you need to double click on the molecule.
- Record the dipole moment and energy given. (In this example the dipole = 3.9 debye and the energy is -0.00947 a.u., the Energy(aq) is not important to us!) Hint: Just click on the pink bond and change the value in the box. Do not define a new constraint at this point. This will confuse the program completely!
- For the higher angles (>120o), you might have to uncheck the symmetry box in the setup calculation menu. However, sometimes it works better if the approach is for the higher angles is from 180o going down. In some cases, the symmetry feature has to be removed and put back in afterwards.
- Using EXCEL, plot the dipole moment and energy of benzil vs. the dihedral angle (use MS Excel, XY Scatter plot). Rationalize the observed trends.
PART IIb: (Infrared simulation, In-lab)
Using the Hartree-Fock (3-21G) method of Spartan 2010, determine the C=O bond length in the following compounds (Do not apply any constraints in this part!):
Compound n[cm-1] benzoyl chloride 1774 benzaldehyde. 1703 N,N-dimethylbenzamide 1646 1. Plot the given C=O stretching frequency vs. the calculated C=O bond distance (Hint: Click on the C=O bond to obtain the bond length). Report the R-value and the equation of trend line. Rationalize the observed trend.
2. Based on the obtained graph, predict the C=O stretching frequency of propyl salicylate (o-(HO)C6H4OCH2CH2CH3), acetophenone (C6H5COCH3), m-toluic acid (m-(H3C)C6H4COOH) and thiobenzoic acid (C6H5COSH). Comment on the results.
