Sapling #18

[lwon Dis2I]

What does it mean when the atoms lie in the same plane?

The problem is below:

Select the correct statement about the relative positions of the hydrogen atoms in the three structures.

The hydrogen atoms of H2CCH2 and H2CCCH2 lie in the same plane.

The hydrogen atoms of H2CCCH2 and H2CCCCH2 lie in the same plane.

The hydrogen atoms of H2CCH2 and H2CCCCH2 lie in the same plane.

[Rylee Mangan 1K]

When atoms lie in the same plane they are parallel to each other. Atoms with even number of atoms are coplanar(lying in the same plane). An even number of atoms are parallel and odd number of atoms means perpendicular. For this example, the hydrogens in H2CCH2 and H2CCCCH2 lie in the same plane because they are parallel.

[Natalie Do 3F]

If you look at each of the three molecules, they have a really similar and linear shape to each other. The only difference is the number of carbons double bonded to each other.

[Annabella_Amato_1I]

Is this something you can only determine by drawing out the shape of the molecule? Determining whether or not the hydrogens are on the same plane I mean.

[Adam_ElSayed_3B]

There is a difference between how the hydrogens are placed on a 3D model depending on whether there are an even or odd number of carbons

[Megan Lu 3D]

Hi! For all atoms to exist on the same plane, we would be essentially be able to connect them all on a 2-D plane (ex: they all could lie on the same sheet of paper). To answer the Sapling problem, we would need to consider whether there are an even or odd number of atoms. When there is an even number, the atoms will be coplanar (they lie on the same plane); when there is an odd number, the atoms will not be coplanar.

H2CCH2 and H2CCCCH2 each have an even number of carbons (2 and 4, respectively), so the hydrogen atoms will be coplanar. Hope this helps!

[David Jen 1J]

I also was very confused with this problem, is there any way it has to do with the number of double bonds as well?

[Rohit Srinivas 2D]

I believe this is figured out by looking at pi bonding. whenever you have an even number there are enough pi bonds to lock the carbon into a single plane. This is because the pi bond does not allow for rotation. Every pi bond is formed at a 90 degree Angle to the other, so even numbers would go back to 180 and odd numbers wouldn't.

[Sameer Chowdhury 3C]

Basically it is asking if the hydrogens on both ends of the molecule are all on say the x axis. Or is one end on the x plane and the other two hydrogens are on the y or z planes.

[Brandon Pham 1H]

I like to think of it as like the x and y axis of a coordinate plane.

[FionaHunter21]

I believe this is figured out by looking at pi bonding. whenever you have an even number there are enough pi bonds to lock the carbon into a single plane. This is because the pi bond does not allow for rotation. Every pi bond is formed at a 90 degree Angle to the other, so even numbers would go back to 180 and odd numbers wouldn't.

Thank you for this! I was reading everything and still confused but this made it really clear and make sense.