Pesky asymmetric N atoms

Posted on October 19, 2009 by alan

I just came across this in the Editor’s Choice section of Science magazine (Oct 2, 2009, p. 19):

Getting a Grip on Nitrogen

Chirality is associated more with carbon than with nitrogen centers, as the latter atoms tend to invert their configurations fairly rapidly on account of their unbonded electron pair. Recently, relatively slow nitrogen inversion was observed in cyclic oligomers of four or six … amino acids … on account of hydrogen bonding among the substituents. Mocquet et al. now show that swapping in a single analogous [amino acid] residue that is chiral at carbon disrupts the collective inversion mechanism and thereby dramatically stabilizes the chrial nitrogen conformations throughout the ring.

Notice how the “editor” misuses the word “conformation” when referring to nitrogen “configuration”? Oh well. Probably a physicist.

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Exam #2 results

Posted on October 19, 2009 by alan

Exam #2 has been graded and is available for you to pick up in Kathy Kennedy’s office.

Kathy will be out of the office on Th-F during Fall Break so please stop by early in the week if you want your exam back. If you would like to meet with me, I will be here the rest of Monday afternoon and most of the day on Tuesday. I will be out of town from W-Su.
Continue reading →

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Polymer humor

Posted on October 16, 2009 by alan

This was forwarded to me today from the EHS office. Acrylonitrile’s formula H2C=CH-CN. Nerd humor based on a CN triple bond.

“Acrylic” is a common textile material. It is favored for its wool-like
feel and commonly used in socks. “Acrylic’ is really polyacrylonitrile.
Polyacrylonitrile is a nice way of saying polyvinyl cyanide. Do you
think anyone would buy socks made from polyvinyl cyanide? If you knock
some socks off the shelf in your local discount store, do not run up to
the clerk and announce, “There is a polyvinyl cyanide spill in aisle
10′.

Enjoy Fall Break!

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Resolving Agents – Achiral? Chiral?

Posted on October 14, 2009 by alan

A great question came my way right after lecture: can resolving agents by achiral?

The short answer is no.
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pKa of Bromcresol Green lab – feedback

Posted on October 11, 2009 by alan

I made two marks on each lab. Report indicates whether the written document was prepared properly. In-lab/Models indicates whether you followed directions reasonably well during the two lab periods.

A number of “unsatisfactory” Report grades were issued. Most of these were related to the graphs. Perhaps a graph was missing. Or perhaps the wrong data was plotted on one of the axes. Or sometimes the data table was missing. (There were many other smaller omissions, like missing lab partner name or missing/substandard reference for published value of pKa, but I didn’t mark off for these.) If your Report grade was “unsatisfactory”, submit a new and improved report to me by Friday, Oct 16, and I will reconsider your grade.
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HW #4 feedback

Posted on October 11, 2009 by alan

First, a confession … I made a mistake on the answer sheet that I posted last Friday. The very first problem asks for the reaction product of HI + 1-butene in the presence of peroxides. The correct (?) answer is 1-iodobutane (the anti-Markovnikov product), but I drew 2-iodobutane (the Markovnikov product) on the answer sheet. I have corrected and posted a new answer sheet, but because my readers had already marked up the homework assignments, ignore any “wrong” marks.

Second, the great physicist Albert Einstein once said something like this in reference to theories of physics, “Everything should be made as simple as possible, but no simpler.” The same should be said about structural formulas, resonance structures, and chemical reactions.
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Updates – Salicylic acid, banana oil labs, and more…

Posted on October 8, 2009 by alan

Salicylic acid experiment. You should go into lab on your own and perform the two activities needed to complete this experiment:

  1. weigh your product
  2. measure its melting “point”

These operations may be performed on any week day (9 AM – 5 PM) between now and the due date for the lab report: Friday, Oct 18, 5 PM. Work outside of these hours, or on weekends, is not permitted because of safety concerns.

Banana oil experiment. We will start, but not complete, the experiment next week. You can expect to get through the work-up and into the early phases of the distillation. Perhaps you can do even more. Most students will complete the distillation and subsequent characterization steps after Fall Break. To prepare for this lab, you should:

  1. Do the usual: read background section in lab manual, prepare your lab notebook, print and complete pre-lab activity sheet
  2. Acquaint yourself with the concepts of workup, extraction, washing, drying, proper use of separatory (“sep”) funnels. The MIT video: Workup I (18 minutes) should be watched carefully. There is also helpful material in Padias.
  3. Acquaint yourself with the concept of distillation. My slides are here. There is also helpful material in Padias.

Homework. The answers to HW #4 have been posted. My readers will do their best to get through these lengthy assignments asap, but they are both taking the Graduate Record Exams (GREs) this weekend and they need to prepare. I have given them additional time to read your work and this may delay return of your problems sets by 24 hours? We’ll see.

The next problem set will be posted sometime tomorrow, but it will not be collected. Answers will be posted next week.

Bring model kit to lecture tomorrow. And please arrive on time since we will be performing a ChemActivity related to Chapter 6.

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Lecture slides – Wed Oct 7

Posted on October 7, 2009 by alan

Slides for today’s lecture are located here.

I’ll be updating this page with information on the rotation barrier in HO-OH later today. Let me know if you would like links to information about conumption/manufacture of polymers, plastics, and petroleum.

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HW #3 comments

Posted on October 4, 2009 by alan

This assignment seems to have set a new “standard” for
stumping students and I found myself writing “please come see me this week”
messages on an unprecedented number of assignments.

First, let me talk about the “come see me” note.
The point of visiting me is quite simple – as your instructor (“study coach”),
I want to understand as much as I can about difficulties that you are having in
my course. Some difficulties are an inevitable part of the learning process.
Others might be avoided, or moderated, by engaging in different study
practices. By talking about this together, I might be able to suggest some places
where your approach can be improved. So please follow up asap on my request to “come
see me”. (And if your homework doesn’t contain such a note, feel free to come
see me. I like the company.) Continue reading →

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Download new HW & experience the Greek Festival

Posted on October 2, 2009 by alan

All kinds of tidbits to share as we enter the first weekend in October:

  • Homework page has been updated with answers to #3 and problems for #4
  • Several folks turned in lab notebooks with their lab reports. Yikes – I wasn’t counting on that. I will try to get those notebooks returned to you during the weekend so that you can prepare them for lab next week. I’ll send emails to specific individuals.
  • The lab manual continues to need updates and I’m trying to catch up with as time allows. For example, I’ve spotted a number of references to last year’s textbook (“Solomons & Fryhle”) that need to be replaced with references to Loudon.
  • Portland Greek Festival starts today and runs through Sunday. If you crave, or just want to try, good cheap Greek food, you can’t go wrong by heading over there for a study break (eating on a budget? skip the “dinner” and buy a gyros or some baklava). It’s an easy trip from campus – just take bus #75 north until you get to the Glisan traffic circle (aka The Joan of Arc Roundabout). Get off at the circle and walk 7 short blocks west to the Greek Orthodox church at the corner of NE 32nd & NE Glisan. If you would like to see the full menu, list of events, and schedule of Greek folk dance performances, follow the link to the official web site.
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