Question

What is the structure of the molecule with the name (E)-3-benzyl-2,5-dichloro-4-methyl-3-hexene?

Answer 1

The structure of (E)-3-benzyl-2,5-dichloro-4-methylhex -3-ene is

Explanation:

The real problem here is determining the (E,Z) configuration of the molecule.

You draw a hexane chain with the double bond between `"C-3"` and `"C-4"`, `"Cl"` atoms at `"C-2"` and `"C-5"`, a benzyl group at `"C-3"`, and a methyl group at `"C-4"`.

Determine the priorities of the groups on `"C-3"`.

• Benzyl. The atoms directly attached to the methylene carbon atom are (`"C,H,H"`).
• 1-Chloroethyl. The atoms directly attached to `"C-1"` are (`"Cl,C,H"`).

1-Chloroethyl has higher priority than benzyl because `color(lime)"Cl"` has a higher atomic number than `"C"`.

Determine the priorities of the groups on `"C-4"`

• 1-Chloroethyl. The atoms directly attached to `"C-1"` are (`"Cl,C,H"`).
• Methyl. The atoms directly attached to the methyl carbon atom are (`"H,H,H"`).
  1-Chloroethyl has higher priority than methyl because `color(lime)"Cl"` has a higher atomic number than `"H"`.

In each case, the 1-chloroethyl group has the higher priority.

These groups must therefore be on opposite sides of the double bond (entgegen).