3.15

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004253593
Posts: 218
Joined: Fri Sep 20, 2013 3:00 am

3.15

Postby 004253593 » Wed Mar 05, 2014 9:22 pm

1,1, bromochlorocyclohexane has a preference for 1 conformation, draw it and draw it undergoing a ring flip

how do you know which preference it has?
is it a chair????

irisc23
Posts: 237
Joined: Sat Nov 23, 2013 3:00 am

Re: 3.15

Postby irisc23 » Wed Mar 05, 2014 9:29 pm

Yes, it is a chair. However, you should also put the bromine (atom with the highest atomic number) on the equatorial. This is done by positioning bromine so that it points horizontally, and chlorine so that it points up (assuming that carbon 1 is like the back of the chair and is pointed upwards). This reduces steric strain. When a cyclohexane undergoes a ring flip, all of the axial atoms become equatorial and vice versa. So when it undergoes the ring flip, you will switch the conformation so that bromine now points down (carbon 1 has now taken the position of the "footrest" of the chair and the axial atoms attached would therefore point down), and the chlorine will be equatorial (pointing horizontally).

Just a recommendation: try doing this with the modeling kit that came with the textbook we bought. In my opinion, it really helps to visualize these things in three dimensions so that I can see what chair and boat look like, or how ring flips occur.
Attachments
1,1- bromchlorocyclohexane.png
1,1-bromochlorocyclohexane

y3chem
Posts: 174
Joined: Fri Sep 20, 2013 3:00 am

Re: 3.15

Postby y3chem » Wed Mar 05, 2014 9:32 pm

it is a chair structure, since boat conformation is most often less stable

y3chem
Posts: 174
Joined: Fri Sep 20, 2013 3:00 am

Re: 3.15

Postby y3chem » Wed Mar 05, 2014 9:41 pm

Br has higher priority because of its higher atomic number
we know that if the higher priority atom is on the vertical bonds of a chair (see pg 107 on course reader), the chair conformation of this compound is less stable, therefore you should have Br on the equatorial (like the previous post) and Cl, which as a lower atomic number, on in a vertical position.
The same thing applies when the ring flips

:)


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