Monday, 15 June 2009

S205: TMA-6

Last and final TMA, and one that gave me considerable heartache! Its mostly on book 10 which is full speed organics.

Question 1 is about the production of biodiesel. On the face of it, this looks a nice simple question. However the mechanism is basically a transesterification, related to saponification (soap making). Now both those words sound long and complex, but actually the reaction is really very straightforward. There are two parts to the question, the first is to predict the products of the reaction.
The second is to draw the mechanism.
Well firstly, I usually need to draw the mechanism to be sure I know what the products are, but thats OK I can do the second bit first. The real issue though is there are 6 marks for the first part, and 19 for drawing the mechanism. Even if I do it in painful detail, I can really make more than 2-3 maybe 4 steps out of the whole thing. For 19 marks, this sounds warning bells that I've misunderstood the question. I returned to the question time and again looking for the missing part, even donwloading a research paper on the topic - but no it appears it really is that simple!

Question 2 is some basic organic reactions to extend alkane chains. One part you need to pick appropriate reagents, the other part two different directions for the same reagent. Fairly striaghtforward, but after drawing the mechanisms of the two reactions, I've got a lot more diagram than Q1, and this is only worth 15 marks for the whole question.

Question 3 is on radical reactions - rather scary reactions that have been tamed in recent years. Gives me a chance to draw fishhook arrows, but its basically derived stuff from the appropriate chapters.

Question 4 is on retrosynthesis. You have to undo the reaction to find the products and a way of bringing it about. It leads you through the steps as part of the questions quite nicely, provided you get the right bits. There are some comments on steroechemistry, and on reagents you might need to bring about the final results. Just a case of working through it really.

So - that is all the coursework done! Just the exam to look forward to :-/
(However - I ended up getting the best mark for this TMA out of the whole course, so Q1 must have been "just that easy").

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