16:40 I don't think that compound (1-bromo-1-chloro-4,4-dimethylcyclohexane) has a plane of symmetry; rather, that compound is achiral because, unlike the other 3 on that slide, it doesn't have any stereogenic centers! Also, if you were to replace either of the 2 methyl groups on carbon 4, the compound would still lack any chirality centers, but would exist in 2 diastereomers (cis or trans)
Both are true-neither of those carbons with wedges and dashes are stereocenters, but the compound also has the plane of symmetry indicated (even in its chair conformation, which is worth drawing out). As to whether carbon 4 would be a chirality center if one of the methyl groups were replaced, I'm not sure. I can tell you that "I was taught" that it would be considered as such, since the "right" and "left" halves of the ring are mirror images rather than identical. However, this is one of the reasons I rant about the term "chirality center"...in cases like this, it doesn't seem to me a useful concept. Thanks for watching!
Can those carbon atoms that lie on the plane of symmetry be chiral even though each has 4 different "things" attached to it?
16:40 I don't think that compound (1-bromo-1-chloro-4,4-dimethylcyclohexane) has a plane of symmetry; rather, that compound is achiral because, unlike the other 3 on that slide, it doesn't have any stereogenic centers!
Also, if you were to replace either of the 2 methyl groups on carbon 4, the compound would still lack any chirality centers, but would exist in 2 diastereomers (cis or trans)
Both are true-neither of those carbons with wedges and dashes are stereocenters, but the compound also has the plane of symmetry indicated (even in its chair conformation, which is worth drawing out).
As to whether carbon 4 would be a chirality center if one of the methyl groups were replaced, I'm not sure. I can tell you that "I was taught" that it would be considered as such, since the "right" and "left" halves of the ring are mirror images rather than identical. However, this is one of the reasons I rant about the term "chirality center"...in cases like this, it doesn't seem to me a useful concept.
Thanks for watching!