Identifying asymmetric carbons?

Question

my teacher said today that the 4 different atoms or molecules attached to an asymmetric carbon should be looked at further when identifying asymmetric carbons, meaning you have to look at everything that is bonded to the atom which is bonded to the Carbon. I still don't understand how to find asymmetric carbons,

especially between glucose and galactose.

Answer 1

If the carbon atom has NO PLANE (mirror-image) OF SYMMETRY, then it is ASYMMETRIC. Just imagine a mirror through each and see if the is a mirror-image form; check in 3-D. Molecules may have symmetry while individual atoms are not completely symetrical (3-D view); CH2Cl2 does; CHClFBr does not. How about F2ClCCClF2? How many different atoms (8 or 4)?

Answer 2

your teacher means you have to look at the entire group attaced to the Carbon in question.

Say you had

CH3 - CH2 - CHCl-CH3

You want to see if the third carbon is asymetric,

If you look only at the ATOM it is directly attached to. It is attached to

1 H,

1 Cl

2 C

If you did it this way then you would say it in not asymetric, because there are 2 Carbon attached.

However, this particular Carbon is asymmetric, what you have to do is think of everything on the other side of the bond as a group. If you do this you get

1 H

1 Cl

1 CH3 group

1 CH2CH3 group

It is easy here to see that it definately has 4 different things attached to it.

Hope this makes sense

EDIT::::::::::::::::::::::::::::::;;;

Your top carbon should look like this: H-C=O

Igrore the little dots, I'm trying to get the bonds in the right place

H-C=O

. . I

H-C-OH

. . I

H-C-OH

. . I

H-C-OH

. . I

H-C-OH

. . I

. .H

So, the middle carbon has 4  bonds so it is bonding to 4 other groups. Write out everything in each group on the other end of each of these 4 bonds.

-H

-OH

-CHOH-CHO

-CHOH-CH2OH

Each group is different, so it is assymetric

Answer 3

well, draw the pic of the molecule.

then consider one C atom. then look upward direction which group(in total) is attached there. Let it be U.

Now look Downwards(D), and Left(L) and Right(R).

if L not=R not=U not=D then the carbon atom is asymmetric. If any 2 or more of the 4 matches(are identical) then the C atom is not asymmetric.