# Where is the mirror plane in 1-bromo-1-chloroethene?

I am studying point groups in inorganic chemistry and having a very difficult time understanding some of these concepts.

In my book, Inorganic Chemistry: Fifth Edition by Miessler, Fischer, & Tarr, I am presented with a table showing that $\ce{CHFClBr}$ is in the $C_1$ point group and has no symmetry other than the identity operation.

$\ce{H2C=CClBr}$ is in the $C_\mathrm s$ point group and its symmetry is listed as having only one mirror plane.

I'm having difficulty seeing this mirror plane. I would have listed this compound as being in the $C_1$ point group. Does this have something to do with the molecule being flat?

• The molecule is planar, so the mirror plane is the mirror plane of the molecule – orthocresol Oct 22 '17 at 21:39
• I would suggest to "play" a bit with different molecules and discover their the symmetry operations and point groups: symmetry.otterbein.edu/challenge/index.html. I also noticed that students with a background in FPS games use to comprehend symmetry operations and elements better:) – andselisk Oct 22 '17 at 22:09
• @andselisk Yeah, I'm way more than halfway through my homework and just now grasping it. Any reason behind the fps game thing? I play fps games and am wondering how it would help understand symmetry. – Melanie Shebel Oct 22 '17 at 23:47
• @MelanieShebel I would surmise that those people are more practiced at certain types of spatial reasoning skills. But there are other ways to develop those as well. – Zhe Oct 23 '17 at 0:02
• @MelanieShebel It's rather subjective, but I suspect that old-school non-linear labyrinth-type maps (such as good old Doom, Quake and System Shock) train spatial thinking and visual memory, and help to grasp flat screen representation of 3D entities faster because you are constantly under pressure and have to react/adapt swiftly. It also might just be my excuse for still playing those games as well, so don't take it seriously:) – andselisk Oct 23 '17 at 0:34