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I would like to ask if the 3D spacing arrangement of atoms in chemical bond configurations are always unique, please?

For example, glycine consists of the set of atoms HHNCHHCOOH. Does there exist a different stable 3D arrangement of this collection of atoms, other than:

enter image description here

What causes this arrangement to be unique? If we throw in and react the ingredients in a different order, such as HHHHHNCCOO, will they all still end up as the same unique shape of regular glycine?

Thank you.

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    $\begingroup$ It is complicated. If we throw in the same atoms in different order, most likely we'll get a bunch of different molecules. $\endgroup$ Feb 25 at 14:58
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    $\begingroup$ There are plenty of other possibilities, like $\ce{H2N-CHOH-CHO}$, or $\ce{HO-NH-CH2-CHO}$, or $\ce{H2N-CO-CH2OH}$, or $\ce{HO-NH-CH=CHOH}$ or $\ce{H2N-CO-CH3}$, etc. $\endgroup$
    – Maurice
    Feb 25 at 15:16
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    $\begingroup$ The word you are looking for is isomerism: it is the phenomenon that given number of atoms can form different stable molecules. Depending on how they are different, there are different types of isomerism. $\endgroup$
    – Greg
    Feb 25 at 15:33
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    – Tragamor
    Feb 25 at 23:30
  • $\begingroup$ sigmaaldrich.com/GB/en/product/aldrich/159034 $\endgroup$
    – Tragamor
    Feb 25 at 23:35

2 Answers 2

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From a given number of atoms, you can usually construct multiple molecules (isomers), so we shall just concentrate on the case where the bond connectivity is the same.

The terms you are looking for are conformation and configuration. The latter is most usually related to double bonds and E/Z isomerism. If we take but-2-ene, for example, it can exist in 2 forms, E and Z. Both are stable and have the same atom connectivity. However, they cannot interconvert between each other - the activation energy is too high.

Two conformations of the same molecule, however, can interconvert between each other (at least at room temperature) and they are both stable (i.e., potential energy minima). A classic case of a molecule is butane, whose conformations can be seen in the picture below.

enter image description here

The anti- and gauche- conformations are both 'butane' and both are stable (even though the anti- is more stable), but have a different 3D arrangement of atoms.

As a sidenote, these can be distinguished at a low enough temperature, at which they cannot interconvert.

Another famous molecule with various conformations is cyclohaxane, with the two stable ones being the chair and the much less common twist-boat.

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The arrangement doesn't have to be unique.

For instance, using your notation, propanol is HHHHHHHHCCCO, but it exists in two forms:

Propan-1-ol:

Propanol molecule with OH atached to an end C.

and Propan-2-ol:

Isopropanol molecule with OH attached in to the middle C.

The difference is where the OH is attached, to an end-C or the middle-C.

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