What are the chiral centres in this molecule?

[fataliz]

Hi, i find that i have some problems identifying chiral centers fast in a ring structures. i have to look very far down the chains to determine, is there a quick fix for this?

For example look at the molecule below.

am i right for these chiral centers? this was one of 4 options for a multiple choice, to ask which molecule has a (S) chiralcenter. so besides this there are 3 others to look at. i can't imagine having to spend so much time just to determine the chiral centers for just 1 of the options, and still having to go throught whether there is a (S) amongst this. where have i gone wrong?

thanks in advance!

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[Cawolf]

5 cannot be chiral because it is planar.

Are you asking which is chiral, or which is s?

 

[EParker37]

If a chiral center is located in a ring system such as this, you can nearly always assume that the groups where other rings are attached are going to allow it to be a chiral center, as in most cases, there will not be an exactly even number of identical groups attached to either side.

@Cawolf is spot on for the rest.

 

[sazerac]

Carbon 3 shows stereochemistry. The order of the substituents for 3 would be north, sw, se, south. That's counterclockwise, but the lowest priority methyl is coming at you, so reverse it and you get (R), right?

Been a while since I've done these.

 

[Cawolf]

@sazerac

I wasn't thinking when I said you couldn't define stereochemistry. I forgot that the hydrogens would be assumed pointing away.

 

[fataliz]

hi all thanks. was too sleepy when i typed this. my nad, number 5 shouldnt be a chiral center, that i know. thanks.

To be clearer, the question is asking which of the following 4 molecules contain a (S) stereo isomer?
So subsequently when i reached this option, i was stumped a little identifying the chiral centers and wanted to check if i identified it correctly.

1) The answer sheet states that D only contains (R) stereoisomer. is it a mistake?

2) i understand that you are suppose to order the substituents. my query is, what happens when you hit a junction? which 'path' do you take there after?
For example, if you look at Carbon 3. say you wanna order the substituents. Carbon 4 is on top. but after that there are 2 paths, which do you consider for the ordering purposes. to the left or right?

 

[fataliz]

Carbon 3 shows stereochemistry. The order of the substituents for 3 would be north, sw, se, south. That's counterclockwise, but the lowest priority methyl is coming at you, so reverse it and you get (R), right?

Been a while since I've done these.

hi, so how did you determine the order so quickly? if you had to countdown the carbons one by one, when you took the SW path and hit the junction, which path comes next?

 

[the_fella]

5 cannot be chiral because it is planar.

Are you asking which is chiral, or which is s?

I thought it's not chiral because it doesn't have bonds to four different things. One bond to each carbon, and then two to the oxygen, which makes it achiral. Idk.

 

[Cawolf]

@the_fella That is a reasonable way to answer the question, but it doesn't really touch on what chirality actually is.

Chirality describes a spatial arrangement that produces non-superimposable mirror images. If something is planar, the mirror image will always be an indentical copy due to symmetry.