Recently in Homework Category

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.

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.

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.)

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.
  

The standard way to think about steric repulsion is very simple. An atom requires space for its electrons. If another atom intrudes on that space, both atoms are unhappy and the energy rises. Steric repulsion.

Unfortunately, concept doesn't quite match reality here. It is so costly for atoms to "overlap" (unless they are bonded, of course) that they rarely do. For example the distance between the end C in butane, C-C-C-C, is practically the same in the relatively low energy gauche conformation (3.1 A) and for the very high energy "methyls eclipsed" conformation (2.9 A). (For comparison, the distance is about 3.8 A in the anti conformation.) We know that the "methyls eclipsed" conformation is destabilized by steric repulsion, but the distance between the methyl groups is still fairly large. What's going on?

I have read all of the assignments that were turned in and I will be returning them in class on Monday. In addition to the comments that my graders and I have put on your assignments, there are two additional things that I want to bring to your attention:

• To make grading go more quickly, my two graders and I have used a set of two- and three-letter codes. These were also used last year and you can find an explanation of these codes at this post from September 15, 2008.

• I made a mistake when writing my answers for HW #1. When I read Loudon 1.39 (problem #6), I mistakenly substituted HCl and HF for CH3Cl and CH3F, respectively. The central point of my answer, Cl makes longer bonds than F, still applies, but my comments about treating atoms as charged particles need to be modified. Come see me if you would like to discuss this or any other matter pertaining to the course.
  

I've been inundated with questions and comments about homework assignment #1, and requests for changes in conference assignments, so I wanted to bring you up to date on these and other items of interest.

40 of you responded to my Doodle poll and the results were really helpful. I am going to try out the following as office hours for this semester:

• Tues, 4-5:30* PM (look for me in the o chem lab as well as in my office)
  
• Wed, 10-12 AM
• Fri, 2-4 PM

This site will be updated periodically during summer '09. You can still look at the entire site, including all of the posts from '08-09, but not much has changed yet. Major changes will get announced by adding to this post. If you have nothing better to do, check back every few days. [last changes posted 8/30/09, see below]

Pre-registration for fall

• You must complete the pre-requisites for Chem 201 before you can pre-register. That means if you took intro chem (the equivalent of Chem 101/102, lecture + lab) at another school this summer, you need to provide evidence of satisfactory completion of these courses to Reed's Registrar's Office before SOLAR will allow you to pre-register for Chem 201. This requirement may create some difficulties for summer students at PSU (and possibly elsewhere) because the PSU summer term ends on Wed, Aug 26 and pre-registration at Reed is Fri, Aug 28. If you bring me a signed note on Th-F, Aug 27-28, from your PSU chemistry instructor (email is also acceptable) that says you have completed PSU Chem 221/222/223 with grades of C- or better, I will allow you to pre-register for Chem 201 by overriding SOLAR. [posted 8/10/09]
  

Changes

• Idiosyncratic study tips updated [posted 8/30/09]
  
• Fast Facts pages have been updated [posted 8/24/09]
• New syllabus [posted 8/24/09]
• New lab schedule. Some (all?) navigation links within the lab manual have been updated. The four pages inside the Lab Info section have been updated and should be read by 201 students before the first lab. [posted 8/15/09]
• New exam schedule [posted 8/12/09]
  
• New homework schedule [posted 8/12/09]
  
• New textbook and study guide/solutions manual [posted 7/6/09]

Summer reading

• "The Promise of a Cure: 20 Years and Counting". The inability of gene therapy to deliver a treatment for cystic fibrosis and the role of conventional (small organic molecule) treatments is reviewed in this interesting, non-technical article (Science, 19 June 2009, 324, 1504-1507, listen to podcast interview with author Jennifer Couzin-Frankel).
• "Antibiotics in Nature: Beyond Biological Warfare". Scientists are challenging the conventional paradigm that fungi and bacteria use antibiotic molecules to kill off microbial competitors. According to these scientists, antibiotics could be used for communication and metabolism (Science, 26 June 2009, 324, 1637-1639).
  

Comments on each problem follow (but not in numerical order) ...

#2 - One of the most common errors on this problem set was working the wrong problem for #2. I have to take some of the blame for this. I wrote "Learning Activity #4", but I meant "ChemActivity #4". Many of you had another idea (Learning Group Problem #4, etc.). Oh well.