Difference between cis- structure and trans- structure..

[LyahFitzpatrick 2E]

I understand that cis- coordinate covalent structures have identical ligands adjacent to each other, while trans- structures have identical ligands across from each other, but how does this affect the function or shape of the molecule, if at all?

[Melinda Luo 2G]

Hi there!

Cis and trans structures affect molecules in various ways. For example, oxalate has both a cis and trans structure wherein that the double-bonded oxygens are either next to each other or opposite each other, respectively. In oxalate, having a cis structure helps the molecule form rings since the single-bonded oxygens are next to each other, and therefore can bind easily to other polar atoms/molecules. If we were to try and form a ring using a trans structure of oxalate, then it would be much more difficult since the trans structure is usually more efficient for molecules that often form long chains.

Hope this helps!

[Anthony Tam]

I think the only specific example of this that you have to remember for this class is the cisplatin and transplatin example we covered in class. Because in cisplatin the two chlorines are on the same side, it is able to form a stronger bond with the DNA (it will form two coordinate bonds whereas transplatin will form 1), stopping cell division.

[Tony Chen 1F]

Another example (outside scope of this class) is cis and trans fat. Trans fat has two H atoms attached to the double bond in the opposite side of the carbon chain, whereas for cis fat the H atoms are on the same side. This slight difference gives trans fat a straight structure which means that it can stack onto each other, making it solid at room temperature. So the difference between cis and trans structure also has an effect on how the state of the molecule (solid, liquid, gas) at different temperatures.

[Trisha Badjatia 2L]

I believe it also changes the polarity of the molecule. If identical ligands are across from each other, the polarity cancels out.

[Ana Luiza S]

Cis ligands can more easily bind as bi (or poly) dentate ligands as the electron pair donor atoms have the correct orientation for polydentate binding. You can see this example with the ligand cisplatin which is used as a cancer treatment. For the trans variation of this ligand, the atoms acting as a Lewis base are on opposite sides of the square planar molecule and so they cannot bind in the bidentate ligand form.