CHAPTER 2: Question 3

 

2D explanations

To determine the stereochemsitry of the alkene, the substituents on each end of the double bond are compared starting with the atoms directly attached to the alkene. At the top of the alkene (as drawn below), the first atoms attached to the alkene are a carbon and a hydrogen atom (shown in red). The first of the CIP rules states that the atom of highest atomic number has precedence (i.e. the C atom), so the ester substituent has the higher priority. Exactly the same two groups are attached to the bottom of the alkene, and the two groups of highest priority (the two esters) are on the same side of the double bond so this is the Z-isomer of the alkene.

The conformation of the diene refers to the orientation of the groups around the central single bond shown in red in the diagram below. Since the two identical substituents (the =CH2) groups are on the same side of the single bond, the conformation is s-cis.

The orientation of the substituents on the cyclohexane ring of the product (i.e. the two ester groups and the two hydrogen atoms) is that they are cis to one another, since the two ester groups are both on the same face of the six membered ring and the two hydrogen atoms are both on the same face of the six membered ring.

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