UPDATE: to address tormuse’s comments below.
This discussion came out of a comment I made about the usage of ‘cis’ to refer to people whose gender identity is more matching with their gender assigned at birth*.
“The chemist in me is glad that this word is being used in this way. :)”
And DM replied, asking about the ‘difference between Cis–trans isomerism and chirality’.
Not knowing if this was a serious question, and not wanting to derail a trans- issue conversation with chemical pedantry, I’m putting my answer in this blog post:
Don’t know if this is a serious question, but I’ll bite. Cis/Trans isomerism (generally) has to do with two Carbons connected by a double bond, with different things at R1/R2/R3/R4.:
R1 R3 \ / C=C / \ R2 R4 R1 R4 \ / C=C / \ R2 R3
These two molecules have the same chemical composition, but because the C=C bond is rigid and does not rotate, they can have different chemical properties.
Chirality is a little bit more difficult to explain using 2-D ASCII Art, but basically:
R1 \ r4--C--R3 / R2
(With r4 at the back, behind the C, with R1/R2/R3 sticking out slightly from the page. #limitationsof2d)
R1 \ r4--C--R2 / R3
Which is a non-superimposable mirror image in 3-D. Even if R1/R2/R3 rotate around the r4 axis, they two molecules will never have exactly the same chemical characteristics (cf. Thalidomide)
*I’m sure I’m using some of these words incorrectly or imprecisely. Please comment to correct me!