trans/cis

[hannahdaijo_4H]

Could someone help explain trans/cis molecules and what dictates which structure a molecule is? The book (7th edition) uses dichloroethene (C2H2Cl2) as an example of trans and cis molecules.

[Albert_Luu3K]

Hello,

The way I imagine trans/cis molecules is that there are two different lewis structures that the molecule would be. To differentiate, which lewis structure is correct and what the molecule they are asking for is, trans or cis is added to the front. Cis molecules like cis-dichloroethene are polar because the dipoles on either side do no cancel each other out. In cis molecules and in cis-dichloroethene for example, the Cl are on the same side of either C atom. Both sides would have dipoles pulling towards the Cl, so they do not cancel. In the trans-dichloroethene, the Cl are on opposite sides attached to their C atom, so even though both have high electronegaticity, they are on opposite sides which cancel each other out. Trans molecules would not be polar. Hope this kinda helps! Google is also a nice tool

[hannahdaijo_4H]

So the only way to identify whether a molecule is trans or cis is by the molecule's systematic name rather than merely by the molecular formula?

[Carlos De La Torre 2L]

yes because the formula for a cis/trans molecule is the exact same, the difference comes in how the atoms are positions which is where the cis/trans part comes in it tells you is the same elements are on the same side or on the opposite side

[Elle_Mendelson_2K]

another thing to note is that cis and trans usually are isomers meaning they have different properties. For example, one isomer can be polar while another can be non polar.