Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Jules18 on December 09, 2009, 05:51:08 PM

Title: Which atoms lie in a common plane?
Post by: Jules18 on December 09, 2009, 05:51:08 PM

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fjournals.iucr.org%2Fe%2Fissues%2F2002%2F01%2F00%2Fom6071%2Fom6071scheme1.gif&hash=e255e11b8a9613d48282eac4cdaf94bfe1c8b866)

Which of the following groups of atoms lie in a common plane? (enter the letter label(s), unspaced--there may be more than one correct):

A. 5,6,7,10  B. 4,5,6,10  C. 7,8,9,10,11  D. 4,5,6,7,10

I entered A because they all seemed to be in the same ring.  But I really didn't know how to approach the question.
Is anyone here more familiar with organic chem than me? 
(pfff it's impossible not to be)

Title: Re: Which atoms lie in a common plane?
Post by: stewie griffin on December 09, 2009, 06:14:25 PM

So really this question is asking "which part of this molecule is flat". A normal sp³ carbon with 4 sigma bonds will be tetrahedral. Once we get some pi bonds (formed from either sp² carbons or sp carbons) we get some "flatness". Thus if you looks at the molecule, how many places are there that can be flat (ie where are there some pi bonds).
Furthermore, the carbons involved in the pi bond are in the same plane. Now here's a hint in case it's not clear...the carbons immediately connected to those carbons in the pi bond are also in the same plane. Once you go out to the second carbon though it's no longer in the same plane (ie carbon 3 is not in the same plane as carbon 5).
Based off of that, what would you answer now?

Title: Re: Which atoms lie in a common plane?
Post by: Jules18 on December 09, 2009, 07:02:36 PM

ok I see, so A B and D?

Title: Re: Which atoms lie in a common plane?
Post by: Jules18 on December 09, 2009, 07:03:47 PM

Also, it asks me for the number of hydrogens and the number of sigma bonds and I got 40 and 71 ... does anyone want to try it and see what they get?

it's a lot of adding tiny little numbers and I probably made a mistake somewhere . 

Title: Re: Which atoms lie in a common plane?
Post by: stewie griffin on December 09, 2009, 07:07:22 PM

Yes A,B, and D would be correct. As far as counting the number of sigma bonds and hydrogens... as long as you understand the general idea you'll be fine. I just don't really feel like counting all those  :)

Title: Re: Which atoms lie in a common plane?
Post by: dein fuhrer on September 11, 2020, 10:03:33 AM

Helped me a lot, cheers from Finland.  :)