Already Asked Questions
I will post answers to questions we receive by E-mail at the course E-mail address:
8-25-04
I was curious if lectures notes are posted on the website so we
can pay attention in class instea of writing frantically.
Yes and no. The rules of the day are posted for each day. I think you will find that between those and the pictures of the day (POTD) which are also posted each day, much of what happens in class is posted. The rest is done at a generally comfortable pace. You will see what I mean when we get to the course material starting Friday.
I'm concerned that I did not receive the email that went out to the whole class last night. Is there anything I should do about that? Am I missing from your list of students?
The class E-mail list is is created automatically from the registrar's information, so my best advice is to confirm with the registrar that your E-mail address listed is the correct one.
8-27-04
I was wondering if you could repeat the last thing you said in class
about the
nuclei being shielded. You said at the end of the statement to keep it
in
mind.
Rule of the day #8 for today: 8. Electron density is induced to circulate in a strong external magnetic field, which in turn produces a magnetic field that opposes the external magnetic field. This shields nuclei from the external magnetic field. The greater the electron density around a nucleus, the more shielded it is, and the lower the energy (frequency) of electromagnetic radiation required to flip its nuclear spin.
I did not catch what the HW was. Was it to do the roadmap or did we have actual problems?
Homework is always listed on the bottom of the ROTD for the day. Click here and go to the bottom of the page.
8-31-04
I have a question about some of the relationships you discussed in class today. I understand that more electron density that a molcules has the less the nucleus feels the effect of the magnetic field. What I don't understand is where on the NMR specturm in falls, further upfeild or further downfield. So if you hafve already answered this question in the handout, but as of right now I have no way to print the handout.
Great question, that is exactly what I will start with tomorrow. By convention, more upfield corresponds to more electron density and therefore more shielded (lower frequency of resonance, i.e. closer to TMS), more downfield corresponds to being in proximity to a pi bond and/or less electron density so less shielded (higher frequency of resonance, farther away and to the left of TMS). Hope this helps.
When we make our roadmaps, should we just stick with the basics (as you have done on your I-35 example) or should we include every reaction, so that for alkenes to alkanes we would include electrophilic addition, halogenation, addition of water, etc.? Thanks for all of your help and clarification in last Thursday's office hours. I'll come again this week since my labs haven't begun yet.
It is best to include all reactions that make or destroy alkanes, alkenes, alkynes, aldehydes and ketones. Use the collection of 610A reactions as a guide. Then on the roadmap be sure to add important considerations such as the key intermediate or transition state (i.e. halonium ion, carbocation, free radical, etc.) and any regiochemistry (Markovinikov, etc.) and stereochemistry (syn or anti addition geometry). This will collect all useful information in an easy to use format for future reference and study.
9-3-04
The NMR homework is not collected is it?
No, not this one. Later, the homework will be collected, but we will give you plenty of warning.
9-7-04
I was having trouble with the last two probs. How are you suppose to figure out the # of hydrogens each peak corresponds to without knowing more info. (specifically the molecular formula)? The numbers at the bottem I assume are the integration areas of each of the peaks but I don't how many H's there are total, so it doesn't help me out.
Actually the integrations do help, as the ratio of integration vaules for the different signals give the ratio of the different sets of hydrogens in the molecule. In doing the problem, I suggest the following approach:
First, look at all the possible structures onteh first page,
and list how many different sets of equivalent H atoms are present in
each.
Second, count the number of signals seen in each spectra and compare that
to the number of different sets of equivalent H atoms in the structures
on the front page. This dramatically narrows your choices for each spectrum.
Third, calculate the ratio expected for each equivalent set and compare
that to the integrations. This should narrow the choices even further.
Fourth, examine the chemical shifts to confirm the signals are in the
correct place.
Fifth, examine the signal splitting patterns as a final check that the
spectrum matches your proposed structure.
9-10-04
I had a question about the Nuclear Magnetic Resonance Imaging technique. I have been in an MRI many times. They often ask us to remove any metal devices (ex. Watches, belts, etc.) Suppose we left the metal on our body, what would happen? I am aware of magnets being attracted to magnets, but I was wondering if the MRI could still irradiate the body. Also, when I was in the MRI machine, they injected, I believe iodine, into me. How does the iodine function in the MRI? I know it is supposed to give better contrast or such, but how does it do it. Thanks.
The metal would be attracted to the magnet, not a pretty thought if your finger was still in the ring. For this reason, surgically implanted metal is always of an alloy that is not attracted to magnets. The iodine was for a cat-scan (CT scan, X-rays). Iodine is a very heavy atom (large number of protons and neutrons in the nucleus), so it stops X-rays. By injecting it into your bloodstream, your circulatory system becomes visible to the X-rays. For the MRI they injected a gadolinium compound. The gadolicium is a lanthanide metal, and acts to modulate the relaxation of nearby water molecule nuclei because gadolidium has a funky nuclear spin quantum number. This is a long story, but the bottom line is that adding this helps the contrast of the MRI image based on where the gadolium compound can get to, versus where it cannot go.
9-14-04
How much of the reactions from 610A will be on the test?
They will only show up in synthesis questions.
Also, just to clarify, when I'm looking at functional groups in the NMR spectrum, how do I know which set of equivalent hydrogens will lie in the range for that specific functional group?
Look for the highlighted H atoms in the table. They are usually directly adjacent to the functional group in question.
I was also wondering if there's any chance that you may hold office hours at a different time.
I will have a review session next Monday evening.
9-23-04
If I am not wrong, I think you have mentioned in class today that we
do not have to worry about addition of Sulfur Nucleophile reaction for
the midterm. Am I right? Or am I fooling myself?
You are correct, the dithiane chemistry will be on the next exam, not this one.
10-7-04
I might be incorrect but I believe that the example in the book 17.1
(d),
the example asks for IUPAC names and states the structure as Chloroacetic
acid.
Shouldn't the IUPAC name be 2-chloroethanoic acid?
2-chloroethanoic acid is the correct IUPAC systematic name. It turns out that some common names are also acceptable as IUPAC, and this is one of them. However, you make a good point and 2-chloroethanoic should have been listed in the book. Good job here!
10-16-04
I understand which ones are the two packets we have to turn in on monday
to get the T score extra point. But are there any of the other ones posted
meant to prepare us for the exam on thursday?
Please let me know - I'd like to get all the extra practice I can!
The other ones are for other midterms/the final. I post them all semester just so they are there when needed.
On page 591, part b, The Wolff-Kishner reaction of Camphor, hydrazine, and KOH in diethylene glycol yields the same product. Shouldn't the carbonyl group of the ring be reduced to a methylene group?
You are absolutely correct. The carbonyl group should have been reduced to a -CH2- group in the product. We try very hard, but sometimes these mistakes make through the editing process.
10-27-04
This question is about the last thing we went over in class today. You
said if
we add 1.0 eq. of NaOEt to the Claisen reaction, only the conversion to
enolate
would go faster, and 0.5 eq of NaOEt would remain after the reaction and
go
wasted. My question is would the amount of enolate converted double as
well (i
know there's only a little bit of it present in the equilibrium)? If not,
why
not (shouldn't doulbe amound of NaOEt place a stress on the equilibrium
and
push it more to the right?)?
Great question. Yes, the amount of enolate would double. It would still be a small amount at any one time and would still react pretty much as fast as it is formed, but it would form twice as fast with twice as much base added.
11-16-04
what chapters are gonna be on the exam? i havent been feeling good the past couple of days and havent attended class since last wed. also, just wondering if there is gonna be class next wedensday ( day before thanksgiving) i know that some profs just cancel class, and i was wondering how you go about it.
The tests will cover everything up through the Friedel-Crafts alkylation reaction. I will have class on Wednesday, but I will only talk about research for those interested. If you are in town it will be interesting, if you are not, you will not miss any material that will be on the final.
11-18-04
is there gonna be nomenclature on this midterm> i believe you said
no in class
since enough people went to the race. i just would like to verify.
Because 66 people ran in the race, there will be no nomenclature.
Will you post the answers to the practice aromatic questions also (if you have the time) because I had some issues with a few of them and I wanted to know exactly what the answers are.
These are going to be assigned for credit over the Thanksgiving holiday, so I cannot post the answers yet.
Is there class next Wednesday?
Yes, I will be talking about my research. Anyone available should find it very interesting and it involves biodefense work. Another way to look at it, we will not be covering new course material.
11-28-04
What time will the review session be on Wednesday December 1st? Also, how many cans of food do we need to bring in to be able to go to the review session? Can we turn in the homework that was assigned over the break on Monday or do we have to wait until Wednesday?
The review session will start at 8:00 PM and go until 10:00 PM, or until everyone runs out of questions. Bring as many cans of food as you feel appropriate. It is not an absolute requirement, but I think this is important and I would like to see 100% of the attendees bring a can or more. Yes, you can turn in the homework on Monday.
12-10-04
Will we be asked to do identify molecules with NMR spectra?
No NMR spectra will be on the final. Spend your time on the other material. However, you should be familiar with the theory behind the NMR experiment, as this is the basis for MRI as well.
