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

Jun 9, 2015

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 $\text{C-3}$ and $\text{C-4}$, $\text{Cl}$ atoms at $\text{C-2}$ and $\text{C-5}$, a benzyl group at $\text{C-3}$, and a methyl group at $\text{C-4}$.

Determine the priorities of the groups on $\text{C-3}$.

• Benzyl. The atoms directly attached to the methylene carbon atom are ($\text{C,H,H}$).
• 1-Chloroethyl. The atoms directly attached to $\text{C-1}$ are ($\text{Cl,C,H}$).

1-Chloroethyl has higher priority than benzyl because $\textcolor{\lim e}{\text{Cl}}$ has a higher atomic number than $\text{C}$.

Determine the priorities of the groups on $\text{C-4}$

• 1-Chloroethyl. The atoms directly attached to $\text{C-1}$ are ($\text{Cl,C,H}$).
• Methyl. The atoms directly attached to the methyl carbon atom are ($\text{H,H,H}$).
1-Chloroethyl has higher priority than methyl because $\textcolor{\lim e}{\text{Cl}}$ has a higher atomic number than $\text{H}$.

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

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