Curved Arrow Press Forum

An organic chemistry forum of Curved Arrow Press. (Oh, would you believe we accept donations.) Registration closed.

You are not logged in.

#1 2008-02-17 13:07:18

orgopete
Administrator

Why is organic chemistry so hard?

I see this question or something like this posted quite frequently. Below are some of my answers.

Offline

 

#2 2008-02-17 13:07:26

orgopete
Administrator

Re: Why is organic chemistry so hard?

I expect you will get a lot of answers for this. Those that found it easy and those that found it hard. Even the instruction is geared for those sentiments. I have helped students who had very difficult problems and those that had very easy problems.

Let me distill it down. For those that find it easy, they focussed on the principles. There are only a few patterns that are varied to explain most of the reactions. On the other side is the camp in which if you can't understand it, memorize it. Some of the books and websites serve this line of thinking.

I can't speak for your school, but the course and expectations can vary quite widely. From my experience, most students succeed with stereochemistry, conformational analysis, nomenclature, etc. They describe static things. If given enough practice, students know what sp3 or axial mean.

Reactions are a different matter. You start with something and end up with something else and the variations are endless. I used reaction mechanisms or mechanistic thinking as a staple of my teaching activities. I also introduced a mechanism workbook to supplement the class. By doing so, I raised my class average on the ACS organic exam by 20 percentile points.

I find it interesting that mechanism based textbooks are in the minority while functional group based books are the majority. A mechanism based book focusses on how you get to the answer and a functional group based book focusses on where you are going. Many students (and professors) resist a mechanism approach. A mechanisms is a logical explanation of the electron movements that lead to the products. I like it. That kind of thinking appeals to me and has worked well with my class.

At the other extreme, some schools emphasize retrosynthesis and can even be rigid in how it is to be formatted. I have tutored some students in schools like that. I mention this because it strikes me as being extremely challenging to try to use reactions you do not know. It is like translating from English with a foreign language dictionary. I would expect organic chemistry to be extremely challenging at those schools.

I cannot predict which type of instruction you will encounter. If you have the ability and have good instruction, you shouldn't have any problem. On the other hand, I had just answered a question in which I explained that organic chemistry has some inconsistencies. Those inconsistencies coupled with a "memorize it" approach to learning can make for a long course.

If you want to learn reaction mechanisms, use "The Language of Organic Chemistry; A Guide to Organic Chemistry Mechanisms" at http://www.curvedarrowpress.com. (Incidentally, I had a summer high school student learning reactions from the book without taking organic chemistry. The book makes the reactions accessible and I believe my results are a reflection of that.)

Answers Yahoo.com post

Offline

 

#3 2008-03-06 01:47:18

orgopete
Administrator

Re: Why is organic chemistry so hard?

Parking
Cycloheptatriene has 6 pi electrons, but it does not fulfill the rules for aromaticity. You must be able to draw resonance structures using all the atoms in the ring. The CH2 group cannot be used, therefore cycloheptatriene is non-aromatic. The radical can use all of the atoms in resonance structures, but it does fit the Huckel rules for aromaticity, namely 6 or 10 pi electrons (2n+2 rule). Therefore, it is also non-aromatic. The anion also can use all atoms to form resonance structures, therefore could also be aromatic, but again the Huckel rules for aromaticity do not fit. It does fit for an anti-aromatic system with 8 pi electrons (2n, n=4). I don't know whether this will be truly anti-aromatic or not. There are many systems that could be consider anti-aromatic, but are able to adopt a conformation such that the electrons do not interact as needed to be aromatic or anti-aromatic. That is, if changing conformations blocks all electrons from becoming part of a higher energy system, it will do so. An example that is often cited is cyclooctatetraene. It forms a puckered shape so it is not planar (one rule for aromaticity) so the electrons do not interact in forming the resonance structures. I would guess that such an anion has been prepared and if the hydrogen were parallel to the pi electrons, then that atom would block resonance with it. The non-bonded electrons could then be orthogonal to the pi system and should not be counted as part of the aromatic system. The effect would be the same as pyridine with its lone pair of electrons being orthogonal to the pi system also.

Offline

 

Board footer

Powered by PunBB 1.2.16
© Copyright 2002–2005 Rickard Andersson

//google analytics added