[Frank Ose]

Which of the following organic molecules (s) contains (s) carbon atoms that are placed in the same plane?

1- C6H5CH3
2-CH3C---C-CH3 (--- is triple bond)
3- CH3CH2CH3

Can anyone explain this question explicitly to me?

Any help would be appreciated.
Thanks in advance!

[Think2Much4UserNames]

Hi there,
you know the number of carbon atoms on the same plane by counting the longest chain of carbon atoms of a Lewis structure/model.

[Frank Ose]

So the answer is obviously 2 and 3?

Their C atoms are all linked together.

[Yggdrasil]

Usually carbon atoms will lie in the same plane if they are sp² hybridized since sp² hybridized atoms adopt trigonal planar geometries.  Molecules that adopt linear geometries also have coplanar carbons.

[Borek]

you know the number of carbon atoms on the same plane by counting the longest chain of carbon atoms of a Lewis structure/model.

Assuming this approach cyclohexane will have 6 coplanar carbons. It has 4 at best.

Assuming this approach 2-methylpropene will have 3 coplanar carbons. It has 4.

So obviously something is wrong.

[Astrokel]

Can you expand on your point borek because i don't get it. cyclohexane have 4 coplanar carbon atoms because of the chair conformation? I don't understand why 2-methylpropene has 4 coplanar carbons?

[Borek]

cyclohexane have 4 coplanar carbon atoms because of the chair conformation?

Doesn't matter if it is chair or boat, there are 4 coplanar atoms and two sticking out, either on the same side or not.

I don't understand why 2-methylpropene has 4 coplanar carbons?

Draw it. What is hybrydization of the central carbon?

[Astrokel]

hello,

what about half-chair conformation, where it has 5 coplanar carbon atoms? Or is it too unstable?

Draw it. What is hybrydization of the central carbon?

it's sp2 hybridised, i got it thanks, i am really bad at visualizing.

[Borek]

what about half-chair conformation, where it has 5 coplanar carbon atoms? Or is it too unstable?

Generally speaking only chair is stable and it dominates in normal temperatures.

There exist also relatively stable twisted conformation, but it looks to me like it even doesn't have 4 coplanar carbons (but I am not sure). Still - there are no 6 coplanar carbons no matter how hard you try

[Frank Ose]

It has been a long time since i last visited this thread.

Thanks for all the explanations, I'm assimilating them.