[Sprinkles11]

Hi there! I need *delete me* I understand IUPAC naming for structures, however I am not sure what the best way is to tackle this structure with R and S naming? Is there any tips to answering this one properly? I understand how to prioritize the 4 separate molecules/compounds attached to the center, but.....any tips? I choose A first, but I know the answer is B. Thank you! 

1.   What is the IUPAC name for the structure below?
 
A)   (R)-3-chloro-6-ethyloctane
B)   (S)-3-chloro-6-ethyloctane
C)   (S)-6-chloro-3-ethyloctane
D)   (R)-6-chloro-3-ethyloctane
E)   None of the choices are correct.

[rucik5]

Hi.
Well, if you know the rules behind prioritizing the substituents on a chiral carbon you just need sort out whether it is R or S.

Check this: http://en.wikipedia.org/wiki/Cahn–Ingold–Prelog_priority_rules#Stereocenters:_R.2FS

If you're still a bit confused, here's a good explanation too (point 3.): http://www.stolaf.edu/depts/chemistry/courses/toolkits/247/rvss.htm

Hope it helps!

[puneet]

The IUPAC name of the compound is (S)-3-chloro-6ethyloctane
the S nature of the chiral centre was obtained by the Cahn-Ingold Rule that if the chiral center has the lowest priority group in the backside of the plane and the rest of the groups follow the anticlock-wise priority, the compound is S .

[fledarmus]

You have four groups attached to C3 - a hydrogen, a chlorine, an ethyl group, and an ethyl-pentyl group. How did you prioritize them, and why did you assign this priority?

[puneet]

The priority is given on the basis of higher atomic mass, and if the masses of the groups attached to the chiral centre are same then the atomic number is preferred.
Cl will get the first priority due to its higher atomic mass,
for second and third priority, we have to check the ethyl and ethyl pentyl group, the linkage of the carbon atom on ethyl group is C-C-H, and for the ethyl pentyl groupit is C-C-C, hence the ethyl pentyl group has an atom of higher atomic number (C) as compared to that of ethyl group (H), hence the ethyl pentyl group is of second priority and ethyl group is of third priority
hydrogen being lightest in atomic mass, gets the least priority