[Nitin_Naudiyal]

Hi,

I have few doubts regarding the Tetrahedral geometry of C atom.
In the Book "Organic Chemistry - by Morrison and Boyd"
Chapter 4 - Stereochemistry
Sec 4.2 Isomer Number and Tetrahedral Carbon.

For an atom Y, only one substance of Formula CH₃Y has ever been found.
For and atom Y and for any atom Z, only one substance of formula CH₂YZ has been found.
Thus out of the three possible structure of Methane i.e. 1)Planar arrangement 2) pyramidal arrangement 3)tetrahedral arrangement.
Only the Tetrahedral one is consistent with this evidence

Please help me understand the paragraph.

[Hunter2]

If it would be planar you can draw 2 molecules  with CH₂YZ, A pyramid would have 5 edges, if its a square pyramid. The tetrahedral is a pyramid with a triangle on bottom and distance all the same, so only 1 CH₂YZ. Chirality you can find only if CAXYZ you have.

[Nitin_Naudiyal]

Any Reference to an Image that will help me understand it.
As i still didnot understand the concept.

[Hunter2]

If you have an atom and 4 substituents are set around it on the same level and the Formula is CH₂XY then you can draw two molecules. One like a cis and one like trans.
A Pyramid has 5 edges so it doesn't fit, and a Triangle Pyramid only fits as a tetrahedron, all substituents has same distance to the atom.
     
                   
       l               l
 - -   - -
       l               l
                   

[Nitin_Naudiyal]

if i have an atom with 4 substituent around it on the same level and the formula is CH₂XY
then if i just vary the position of X,Y , i can draw many structures.


Please Pardon me if the question sounds silly.

[sjb]

if i have an atom with 4 substituent around it on the same level and the formula is CH₂XY
then if i just vary the position of X,Y , i can draw many structures.


Please Pardon me if the question sounds silly.

Try making models? What is the (rough) bond X-C-Y bond angle?

[Dan]

if i have an atom with 4 substituent around it on the same level and the formula is CH₂XY
then if i just vary the position of X,Y , i can draw many structures.

This is exactly what the question is driving at. You have shown that there are two stereoisomers of square planar CH₂XY (the first and last structures in your picture are the same), cis and trans.

You can show that you would also expect stereoisomerism if CH₂XY was trigonal pyramidal.

Only for the tetrahedral arrangement would you predict no possible stereoisomers.

[Nitin_Naudiyal]

So, if i consider CH₂XY, in Planar Model it can have only two Models.
Shown in the Picture below.

And is the same valid for a Pyramidal Structure.
Please correct me if i am wrong.

Thank you for your help

[Dan]

Yes, I think so.