Student Name: Jennifer
Student Email: jknowles_1@yahoo.com
Submitted from:
Dr. Mouser, Do you know when the lab manual will be available?
Answer:
It is now available.
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Professor Mouser, I am working on GC analysis and I am trying to understand the two different response correction factors. On page 96 of the reader the diagram shows areas for the different components that differ from the uncorrected areas given in the below table. Why is this? Also, In the mole % table at the bottom of the same page, where does the 37,415 used in the denominator come from? I summed the uncorrected and corrected areas as a guess and was off by 2500 and 150, respectively. Lastly, how does one determine the weight response factor? It is given to us on page 97 and I don't know where it came from. Thank-you.
Courtney, a) The diagram is the standardized solution (and from this the correction factor is calculated) and the table with the uncorrected values in a nonstandardized sample. b) the 37,415 is slightly off. The correct value is 37,571 (which is 14,300 + 5896 + 17,375). You do not need to know the weight response factor.
Dr. Mouser, I am confused about the difference between 13C NMR and 13C[H] NMR. How does Proton NMR relate to either one? Is 13C[h] NMR simply a synonym for Proton NMR? Thanks.
13C{1H} NMR is not the same as proton NMR. We did not cover proton NMR in lecture. However, a proton can influence the carbon NMR.
Did you know that I don't memorize anything I can look up?
Did you look up your name today?
Dr. Mouser, Do we having the same room for the final? Thanks. Catherine
Catherine, Correct, the final exam is in CS 50 (same as lecture).
Hi Doctor Mouser I have a few questions. 1. Are you going to provide any tables (IR, NMR, DEPT) on the final? 2. what was the purpose of adding Ligroin on the Diels Alder Experiment? 3. Why did we add two acids to the Cyclohexanol in the Elimination Reaction experiment? Thank you, Lilian
Lilian, 1. cannot answer this question since is was sumitted to late. 2. Ligroin/ethyl acetate mixture was the solvent mix needed for the Diels-Alder product to crystallize out of it. 3. The phosphoric acid is used to dilute the conc. sulfuric acid. Sulfuric acid is a stronger acid than phosphoric acid. This reaction does not go if only phosporic acid is used. However, if only conc. sulfuric acid is used then byproduct formation if favored resulting in a low yield of cyclohexene.
hello prof Mouser, i was wondering for the prelab question you asked for the eugenol lab, number 2a, i dont understand why when you have eugenol in the aqueous layer, that you first neutralize it with adding HCl and then extract with diethyl ether. Why cant you first extract with diethyl ether and then add HCL to neutralize.
The phenoxide derivative (the deprotonated eugenol) is not soluble in diethyl ether.
Professor Mouser, I am working on GC analysis and I am trying to understand the two different response correction factors. On page 96 of the reader the diagram shows areas for the different components that differ from the uncorrected areas given in the below table. Why is this? Also, In the mole % table at the bottom of the same page, where does the 37,415 used in the denominator come from? I summed the uncorrected and corrected areas as a guess and was off by 2500 and 150, respectively. Lastly, how does one determine the weight response factor? It is given to us on page 97 and I don't know where it came from. Thank-you.
Courtney, a) The diagram is the standardized solution (and from this the correction factor is calculated) and the table with the uncorrected values in a nonstandardized sample. b) the 37,415 is slightly off. The correct value is 37,571 (which is 14,300 + 5896 + 17,375). You do not need to know the weight response factor.
If I understand correctly, reverse-phase TLC is when the stationary phase is more polar than the mobile phase, as opposed to the lab TLC, in which the silica gel is less polar. However, in the answer key for the Winter 2001 Final problem 6, you said that a "reverse phase plate's stationary phase is non-polar as compared to the polar stationary phase if silica plates used in lab." Is this a typo or am I mis-understanding reverse-phase TLC? Thank-you.
Courtney, The answer key is correct. See page 75 of Landgrebe.
Hello, I had a question about the IPSO carbon. It is mentioned on page 56 of the reader, but there is not much of an explanation for it. Also, how does chemical shift relate to this? Thanks.
Edward, the explanation was given in lecture.
professor in my IR for tetraphenylcyclopentadienone, i got peaks at 3856, 3753, 3678, 3651 what are these due to? The only possible explanation I can give for them is that it may be a little bit of water that was still present in my product that was detected in the KBR pellet. Is this correct?
Are these signals significant or are they noise? What is their intensity (%T). Are they broad or sharp? The OH peak is broad and easily identified. If there are a lot of random fluctuations then they should be ignored. If the concentration of the sample is too low (which is very common when a KBr pellet is used) then distinguishing signals (those peaks we want) from noise can sometimes be difficult. Yes, there is a good chance moisture (common for KBr pellets) is present. The signal will be broad and ideally weak. [FYI: The American Heritage Dictionary defines noise as "a random and persistent disturbance, that obscures or reduces the clarity of a signal." A more obtuse definition for noise is any part of the observed electrical signal that is unwanted.]
For the stereochemical reduction of Camphor, how do you know which approach is favored(exo,endo? Can this be determined by experiment only?
This was covered in lecture.
What is Parylene, it is found in the background IR spectrum?
A polymer coating commonly used as a protective coat on electronic devices against moisture, corrosives, dust,and other harmful materials. See "http://parylene.net/parylene_coating.htm" for different types.
For the IR sprctrum of Isoborneol, what is the difference between the two solvents CCl4 and CH2Cl2. Why do we see a unsaturated C-H bond at 3054?
Again, the difference and the 3054 peak was covered in lecture.
For the stereochemical reduction of Camphor, how do you know which approach is favored(exo,endo? Can this be determined by experiment only?
This was covered in lecture.
professor in my IR for tetraphenylcyclopentadienone, i got peaks at 3856, 3753, 3678, 3651 what are these due to? The only possible explanation I can give for them is that it may be a little bit of water that was still present in my product that was detected in the KBR pellet. Is this correct?
Are these signals significant or are they noise? What is their intensity (%T). Are they broad or sharp? The OH peak is broad and easily identified. If there are a lot of random fluctuations then they should be ignored. If the concentration of the sample is too low (which is very common when a KBr pellet is used) then distinguishing signals (those peaks we want) from noise can sometimes be difficult. Yes, there is a good chance moisture (common for KBr pellets) is present. The signal will be broad and ideally weak. [FYI: The American Heritage Dictionary defines noise as "a random and persistent disturbance, that obscures or reduces the clarity of a signal." A more obtuse definition for noise is any part of the observed electrical signal that is unwanted.]
Hello, I had a question about the IPSO carbon. It is mentioned on page 56 of the reader, but there is not much of an explanation for it. Also, how does chemical shift relate to this? Thanks.
Edward, the explanation was given in lecture.
1.In the prelab for DA you have the 1st question that relates to formation of products. you have the second reaction where no product is formed and you have the 1st reaction where a product is formed. Why isnt the product formed in the second rxn? is it because of sterics??? And for the HOMO and LUMO interpretation for prediction of major minor products, wouldnt you have to know the energy of the HOMO and LUMO? and if so, will they be given on the exam?? 2. In CR you have in the Eugenol section the chemical shifts of the ipso carbons. are we responsible for these for the NMR sections?? pg 56 of CR 3. For clarification, i wasnt sure if the DEPT table will be given on the exam or not. ON one of ur practice exams in the reader you have the DEPT logic table ( ie. up/ down of the different DEPT and correlating CH groups). Will it be given on exam??
1. The s-cis conformation of the diene is required for a Diels-Alder reaction. In reaction 2, the s-cis conformation is highly unfavored due to the steric interaction of the tert-butyl groups. 2. yes 3. DEPT logic table will not be given.
In the course reader appendix u have the GC molar response factors (correction factors) are we responsible for utilizing correction factors for GC analysis?? And,does it matter which compound we choose from the GC results as the standardized one for the correction?? ie in the CR they choose out of the 3 compounds the one with the area that is medium compared to the other 2.
Yes, you need to know how to correct. No, it does not matter which peak is used.
dr. mouser, are we responsible for the DEPT?
Yes.
in lecture you didn't go over proton NMR. and I think you said we didn't have to know it for the final.. is this correct? thanks
You should know Carbon-13 NMR and DEPT . Proton NMR will not be on the final.
Hi professor mouser, i was trying to do the nmr spectra interpretation for the aldol product, but i realized that the aldol product is not labelled(pg. 64 of the reader). Is the molecule supposed to be labelled (a, b, c, etc.)?
Please assign your own letter scheme for the interpretation. a, b, c ... works best.
Do we have a post-lab write-up due next week? If so, what should we include in it?
Unless your TA requested a post-lab, one is not due since you do not have all of your data (TCL, IR, UV-Vis) for the aldol experiment.
Hi Prof. Mouser, Do we need to know the molecular weigh of Cloves in order to calculate the percent yield of Eugenol? If we do, can you help us. I can't find it. If we do not need it, can you please give us some clues. Thank you very much. Uyen
You cannot calculate the mw of cloves since it is not a single molecule. Calculate the percent isolation (in grams). E.g., weight % recovery = (Eugenol in grams / Cloves in grams) x 100
In lab, when we added methylene chloride to the eugenol distillate, the top layer is the cloudy aqueous layer and the bottom (clear) layer is the organic layer consisting of methylene chloride and eugenol. Eugenol is the essential oil, so why did the top aqueous layer look oilier than the bottom layer (which had the eugenol and didn't look oily at all)?
This is because methylene chloride and water from an emulsion when mixed. An example of this that you may be familiar with is vinegar and oil (salad dressing) -- when mixed they form an emulsion which results in a cloudy look.
For the isolation of Eugenol using methelene chloride, why would the Eugenol end up in the methylene chloride solution?
If I understand your question, you are asking why not use methylene chloride to extract eugenol from cloves. This does not work. The cloves swell in water which is necessary in extracting out the eugenol. This is also true in the case of trying to isolate caffeine from tea leaves. Though caffeine is over 50 times more soluble in methylene chloride than in water, caffeine is not isolated when methylene chloride is used. Like cloves, the tea leaves swell in water which aids in extracting the caffeine out.
For crystallizing our products, how long should we let it cool? What should be the minimum and maximum amount of minutes we should let the solution cool before disturbing it? Should we wait at least 15 minutes and then if it's still not crystallizing scratch the inside walls of the container and then put it in the ice bath? It's just because we're doing the crystallizing again for next week and we don't want to repeat the same mistakes! Thanks.
Allow to cool to room temperature. I'm guessing this will take 10-15 minutes. If crystals do not form after 2 minutes of cooling, then stratch the bootm of the flask with a glass rod. Repeat this until formation of crystals are observed. Follow the procedure given on p. 42 of the course reader.
for the boiling point factor in gas chromatography, what would be a good range for similar boiling points? (like, would you consider a boiling point of 131 to be close or similar to 140? how far apart do they have to be before they are no longer so similar?)
This is an excellent and complex question that does not have a definitive answer (like most things in life). It ultimately depends on the *degree* of the polarity of the compounds and the type of stationary phase used. IN GENERAL, a bp of 131 and 140 should be considered to be close enough that the difference in polarity of these compounds should be factored in. HOWEVER, if the *difference* in polarity of these two compounds is negligible, then the lower boiling point component will have the smaller retention time.
The retention time (and resolution) are dependent on several factors (see pp. 96 and 97 of Langrebe). Thus, the conditions used for the gas chromatogram in the reader and very unlikely to be the same conditions used for your chromatogram. We used the same column so the retention time, in this case, would differ if the flow rate of the carrier gas was not the same and if the column temperature differed. [E.g., if the flow rate was faster, the retention time would be shorter.] Assume the sample size and injection time differences are negligible.
Hi, Dr. Mouser. In the last lab (synthesis of cyclohexene from cyclohexanol), why did we have to use both phosphoric acid and sulfuric acid? Why isn't the sulfuric acid good enough to carry the reaction when it's already a concentrated acid solution? Why use 85% phosphoric acid too?
Phosphoric acid is a weaker acid. For secondary and tertiary alcohols, milder conditions promotes the elimination.
HI Dr. Mouser Could you explain more about LUMO beside what you said in lecture about it?. Also, what effect does LUMO have on the approach the Nuclophile uses when it attacks Camphor (i.e. the endo or exo approach)? Thanks
Knowing where the molecular orbitals lie will help in attempting to determine which product is favored. IN the case of camphor, the LUMO's (lowest unoccupied molecular orbital) Pro-R face (endo approach) is more exposed. I will spend considerable time in lecture (April 28) on MO theory.
hi prof mouser, i was wondering if the spartan assignment that we have assigned in the prelab is supposed to be done before the lab or if we were going to do it in lab. thanks
Before lab.
Dear Prof. Mouser, Where can I find the guide line for post-lab of the 2nd week experiment? Thanks. Uyen
Course reader, Appendix I has general guidelines.
Hi Prof Mouser,' which chemical properties would you like us to look up for the pre lab? (melting points?)
Only those physical properties that are pertinent to the experiment. For example, the mp of camphor, borneol and isoboneol is practical since the product could consist of the aforementioned cmpds. The boiling point of diethyl ether (or any solvent) is typically reported so one is aware of its volatility.
Hi, in lecture today you mentioned a short NMR review. When will that be?
It was on Friday.
Hi, Dr. Mouser. In the last lab (synthesis of cyclohexene from cyclohexanol), why did we have to use both phosphoric acid and sulfuric acid? Why isn't the sulfuric acid good enough to carry the reaction when it's already a concentrated acid solution? Why use 85% phosphoric acid too?
Phosphoric acid is a weaker acid. For secondary and tertiary alcohols, milder conditions promotes the elimination.
Dr. Mouser, Do you know when the lab manual will be available?
It is now available.