[alphaomega]

Hello all.

I'm studying for an upcoming Orgo exam and in a previous test they had the attached question.  Unfortunately, I can't find a similiar example in either my book or the internet, hopefully I can get some help here.

I'm not sure how assigning priorities works when you go around a ring and you can choose where to go next instead of following a line.  More specifically, I'm not sure how to prioritize like h where you can go up to H3C then over to another C and connect with the other arm.  I'm not sure if that makes sense but I'm sure someone here has encountered a similiar problem in the past and can advise me on the correct naming procedure.

Thanks for the help.

[Dan]

I expect that in the case of h, priority of quaternary centre > tertiary centre > secondary centre.

[alphaomega]

Good call.

But I don't think that that same idea can be applied to f.

Again, thanks for the help.

[Dan]

It can in part.

For centre f, the O.... group is obviously highest, then you have a C double bonded to O taking next priority, then you have a quaternary C(with no adjacent heteroatoms), and a tertiary C (with no adjacent heteroatoms).

[alphaomega]

Thanks again.  I think that with that basing I only have one more question.  I'm not sure how to name the circled Carbon (sorry to keep asking but I think after this I can extrapolate the answer to any other question I'm likely to encounter on this exam.

[Dan]

Ok, you have:

H
N
C (adjacent O, As)
C (adjacent S, As)

You should be able to put those in order of priority easily.

[swati]

  Please can someone check my answer for the first ques
a : Z
b : ?
c : R
d : S
e : S
f  : R
g : S
h : S

Also I don't understand how b is a chiral centre ?

[FeLiXe]

swati: I got the same result

"b" definitely has four different carbon substituents

the one with F ranks first
the one with =C and -C second
the one with -C third
and the methyl fourth

therefore it's S

[swati]

Thank You FeLiXe 

the one with =C and -C second

I forgot the -C attached to it , so I thought that it has 2 same groups and thus it is not a chiral centre.

[FeLiXe]

sure

thanks for writing my name right, so it looks like elements