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Random OCR A-level organic mechanism reactions paper 3

How do I tackle the random organic mechanism reactions given in OCR A-Level chemistry Paper 3? because it is confusing to understand it, is there any tips or documents or like lists which OCR has provided in which random reactions they could assess us on in paper 3 which is outside the spec?
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All you really need to know is how many bonds different atoms form, including when they have a formal charge, and what nucleophiles, electrophiles, and curly arrows actually are. From there, the challenge in these types of questions is the problem solving aspect, so be analytical when looking for differences between the different molecules in each step, deducing how it goes from one structure to the next.

Using question 6(c) on the 2020 unified paper as a worked example:

It says that "the hydroxide acts as a nucleophile" in the question, so you know a curly arrow can be drawn starting from the lone pair on the hydroxide. To know for sure where it goes, you can see on the next box it has to go to the sulphur atom.

Looking at the next box you can see that what was a neutral, double-bonded oxygen atom at the top of the molecule is now an anionic, single-bonded oxygen. This means that one of the bonds has broken and both electrons has gone to the oxygen. This also saves the sulphur from being bonded to more than 6 groups in the first step.

Looking at the third box, the methoxide has split off, so the electrons in the S-O bond have gone to the oxygen, and the electrons on the anionic oxygen have come back down to reform the double bond.

In the last step, the methoxide steals a hydrogen from the sulphonic acid, which can be shown as a curly arrow from the oxygen in the methoxide, and a curly arrow to show the breaking of the O-H bond.


I hope this helps (:
Original post by himdjkwndn234
How do I tackle the random organic mechanism reactions given in OCR A-Level chemistry Paper 3? because it is confusing to understand it, is there any tips or documents or like lists which OCR has provided in which random reactions they could assess us on in paper 3 which is outside the spec?

Hi! I did my a levels last year- I used chemguide a lot to try and get a better understanding (I found the questions really difficult also- I was with WJEC tho). Practice as many questions as you can. You likely know this anyway so sorry if this doesn't help 🙂 https://www.chemguide.co.uk/

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