[pressplay312]

Greetings,

I tried searching the internet and this board, and I've been stuck on this specific problem for the past hour.  Using the asymmetric carbon closer to you, how do you prioritize the groups?  H is #4, and the C double-bond is #1, but how do you determine #2 and #3?  The solutions manual says that asymmetric carbon is R, and I can infer #2 and #3 from that, but I don't understand how it was found.

Here's the compound:




Thanks a lot.

[discodermolide]

Greetings,

I tried searching the internet and this board, and I've been stuck on this specific problem for the past hour.  Using the asymmetric carbon closer to you, how do you prioritize the groups?  H is #4, and the C double-bond is #1, but how do you determine #2 and #3?  The solutions manual says that asymmetric carbon is R, and I can infer #2 and #3 from that, but I don't understand how it was found.

Here's the compound:






Thanks a lot.

It's name is (1R,4S)-bicyclo[2.2.1]hept-2-ene
Priority 1 you have correct, priority 2 is the chain going to the bridging carbon, priority 3 is the chain to the left of the H atom.  which gives  (R)  for the atom you show

[pressplay312]

But what is the thought process in giving the bridged carbon a higher priority than the side chain?  I'm following the directions in the book, to first check the atoms directly attached to the asymmetric C.  Since the bridge and the left side-chain carbon are the same, it says to move along the chain.  The bridge chain is:

C* --- CH2 --- CH

The side-chain is:

C* --- CH2 --- CH2 --- CH

How does the bridge get priority over the side chain?

[discodermolide]

But what is the thought process in giving the bridged carbon a higher priority than the side chain?  I'm following the directions in the book, to first check the atoms directly attached to the asymmetric C.  Since the bridge and the left side-chain carbon are the same, it says to move along the chain.  The bridge chain is:

C* --- CH2 --- CH

The side-chain is:

C* --- CH2 --- CH2 --- CH

How does the bridge get priority over the side chain?

They are not the same count the number of C atoms round to the double bond, via the bridge it is 3, via the chain 4
Look up the Cahn-Ingold-Prelog rules

[BluePill]

At the end of the bridge chain, it is also connected to two other C atoms. While the left side chain is only connected one C atom.

[fledarmus]

But what is the thought process in giving the bridged carbon a higher priority than the side chain?  I'm following the directions in the book, to first check the atoms directly attached to the asymmetric C.  Since the bridge and the left side-chain carbon are the same, it says to move along the chain.  The bridge chain is:

C* --- CH2 --- CH

The side-chain is:

C* --- CH2 --- CH2 --- CH

How does the bridge get priority over the side chain?

It isn't the bridge that gets priority, it is the second carbon along that chain. Go one step at a time -

The bridge chain is:

C* --- CH2

The side-chain is:

C* --- CH2

(Identical to this point)

The next carbon for the bridge is the other assymetric carbon, which is attached to one hydrogen and two oxygens. The next carbon for the side chain is another methylene, attached to two hydrogens and one carbon. The bridge has priority.

Looking at the first point of difference, the bridge chain is:
                         C                         
                       /
C* --- CH2 --- CH --- C

The side-chain is:

C* --- CH2 --- CH2 --- C

[pressplay312]

THANK YOU so much everyone.

THANK YOU!

[bolo]

Why do you need to give the name including configuration on all chiral carbons? There is no other option with a configuration for this alkene and simply bicyclo[2.2.1]hept-2-ene means the same structure.

[fledarmus]

Why do you need to give the name including configuration on all chiral carbons? There is no other option with a configuration for this alkene and simply bicyclo[2.2.1]hept-2-ene means the same structure.

The original question was how to prioritize the groups on the carbon, not how to name the structure.

That being said, you are right - this is a meso structure with a plane of symmetry down the middle, and the mirror images are identical.