Hi, this is a sterechemistry problem. If you have a fisher projection problem with Ch3 at the top, Cl on the left, ethyl group on the right, and a CH double bonded to a CH2 (CH=CH2)on the bottom, it is an S nomenclature correct?

I figured out that Cl is 1st priority, and CH3 is 4th priority....but can you explain to me why the ethyl group is of higher priority than the CH=CH2?

To determine the priority between the ethyl group and the CH=CH2 group in the Fischer projection, you need to use the Cahn-Ingold-Prelog priority rules. These rules help determine the priority of substituents based on the atomic number of the directly bonded atoms.

The Cahn-Ingold-Prelog priority rules compare the atomic numbers of the substituents connected to the stereogenic (chiral) carbon atom. The higher the atomic number, the higher the priority of the substituent.

In this case, let's compare the substituents attached to the stereogenic carbon atom:

1. Cl (chlorine)
2. CH2 (ethyl group)
3. CH (double-bonded to CH2)
4. CH3 (methyl group)

According to the Cahn-Ingold-Prelog priority rules, the atomic number of chlorine (Cl) is higher than carbon (C), and carbon is higher than hydrogen (H). Therefore, Cl is the highest priority substituent.

Next, you compare the ethyl group (CH2CH3) with the CH=CH2 group. Both the ethyl group and CH=CH2 group contain carbon atoms bonded to hydrogen atoms. Since the atomic number of carbon is the same in both cases, we have to look at the atoms directly attached to the carbon.

In the case of the ethyl group (CH2CH3), one carbon atom is bonded to three hydrogen atoms (3 H's), while the other carbon atom is bonded to two hydrogen atoms (2 H's). Whereas in the CH=CH2 group, the carbon atom is bonded to only one hydrogen atom (1 H). Again, according to the priority rules, the carbon atom bonded to three hydrogen atoms has a higher priority than the carbon atom bonded to two hydrogen atoms, which in turn has a higher priority than the carbon atom bonded to one hydrogen atom.

Therefore, in the Fischer projection given, the ethyl group (CH2CH3) has a higher priority than the CH=CH2 group.

To summarize, the priority order for the substituents in the Fischer projection example is: Cl > CH2CH3 > CH=CH2 > CH3. Therefore, this compound follows the S nomenclature.