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Free radical substitution

I've always struggled with understanding where to put the dot for the free radical substitution mechanisms especially for longer chains. Pls can someone help me understand why the dot is where it is and how would I be able to recognise this quickly in an exam
Thank you
Original post by Animal lover :))
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The reason that in the mark scheme the dot is drawn on the carbon in •CF3 is because that’s where the unpaired electron is. You can also write CF3• and most examiners would know what you would mean and will still give you all the marks allowed, but it’s rather dodgy notation and is best avoided in my opinion.

Carbon atoms need to form four bonds to obtain the full outer shell. In •CF3, the carbon only makes three bonds - one to each F, so it must have an unpaired electron on it.

With monatomic radicals, such as the bromine radical, both •Br and Br• are acceptable.
Original post by UtterlyUseless69
The reason that in the mark scheme the dot is drawn on the carbon in •CF3 is because that’s where the unpaired electron is. You can also write CF3• and most examiners would know what you would mean and will still give you all the marks allowed, but it’s rather dodgy notation and is best avoided in my opinion.
Carbon atoms need to form four bonds to obtain the full outer shell. In •CF3, the carbon only makes three bonds - one to each F, so it must have an unpaired electron on it.
With monatomic radicals, such as the bromine radical, both •Br and Br• are acceptable.

Makes sense, thank you!

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