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So I was practicing for exams, and this is the specific question.enter image description here

I get that structure 2 is possible through polymerization and 3 doesn't fit to be the polymer of cyclohexene. I'm kinda consfused about 1 tho, I see that the double bonds have broken and joined with another cyclohexene, but I'm not sure about how that works. Like, is it similar to the addition of electrophiles..if so why isn't this seen with non-cyclic alkenes?

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    $\begingroup$ You're going to need an initiator of some kind. Probably a radical generator. That radical will begin a chain reaction that propagates by adding into the double bond to produce a new secondary radical. $\endgroup$
    – Zhe
    Commented Oct 31, 2016 at 20:40
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    $\begingroup$ 1 is essentially a cyclic form of 2 with $n = 1.5$. So theoreticly, it could form. $\endgroup$
    – Jan
    Commented Nov 2, 2016 at 1:42
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    $\begingroup$ $n = 0.75$ of course. Not sure where my brain was in November 2016 … $\endgroup$
    – Jan
    Commented Dec 26, 2017 at 15:29

2 Answers 2

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I'm fairly sure this question is merely testing one on their ability to count atoms. If the structure has a chemical formula of $\ce{(C6H10)_m}$ where $m \in \mathbb{Z}^+$, then it is – at least in principle – a possible polymerisation product of cyclohexene $\ce{C6H10}$. Whether it is formed in real life is a different question, but my belief is that that is not part of the question, so you're probably overthinking this if you're wondering about how exactly 1 is formed.

1 ($\ce{C18H30} \equiv \ce{(C6H10)3}$) and 2 ($\ce{(C24H40)_n} \equiv \ce{(C6H10)_{4n}}$) fulfill the above criterion, but 3 ($\ce{(C21H36)_n}$) does not.

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    $\begingroup$ I think OP went further from his answer - this isn't homework or overthinking, but curiosity about actual trimerisation reactions. $\endgroup$
    – Mithoron
    Commented Dec 30, 2017 at 1:03
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    $\begingroup$ It's overthinking for the purpose of answering that question, so I decided not to talk about it - however, if we don't restrict ourselves to that question, it's certainl ynot a bad thing to be curious. $\endgroup$
    – orthocresol
    Commented Dec 30, 2017 at 1:16
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This is a less mathematical, and thus slightly simpler, alternative to the user orthocresol's answer.

There's absolutely no need to get confused when coming to addition polymerisation questions. When I learnt about this reaction in my chemistry class this year, my chemistry taught us that a very simple way of handling the question is using this converting to "H form" strategy: Break the $ \pi $ bond and draw the substituents and the two carbons in the shape of the letter H, as shown in the image below. Notice that each of the two carbons have only formed three bonds and each can make another single bond to another atom.

enter image description here

Image source: https://getrevising.co.uk/https_proxy/747

enter image description here

For your question, the 'H form' of cyclohexene is shown above. Now, it is very easy to see that 1 is in fact possible because you are connecting three of these 'H units' in a circular fashion.

Actually, for this particular question, this conversion to the "H form" strategy may seem trivial but for alkenes where the substituents may be "ugly"-looking carbon chains, this strategy can be prove to be very useful.

I hope you find my answer insightful.

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