(b) Compound Y is a naturally occurring vanilloid found in the oil of the ylang-ylang plant. It has a molecular formula $$ \mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}_{2} $$ and has stereoisomers. Draw and label the structures of the stercoisomers of compound Y . modificd 2013/11/3

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$$
\textbf{Compound Y: Isoeugenol}
$$

The molecular formula $$\mathrm{C}_{10}\mathrm{H}_{12}\mathrm{O}_{2}$$ and the “vanilloid” character (i.e. an aromatic ring bearing a hydroxyl and a methoxyl group) indicate that compound Y is the substituted phenol

$$
\text{4-(1-propenyl)-2-methoxyphenol}
$$

in which the propenyl side‐chain is attached at the para position relative to the hydroxyl group. (By convention the numbering is chosen so that the hydroxyl is at C1.) Thus the benzene ring has

• a hydroxyl group at C1,  
• a methoxyl group at C2,  
• and a propenyl group $$\ce{-CH=CHCH_3}$$ at C4.

The propenyl substituent has a carbon–carbon double bond that can exist in either of two configurational isomers (geometric isomers). In the structure, the double bond lies between the benzylic carbon (attached to the ring) and the next carbon. Its two isomers are designated as follows:

---

$$
\begin{array}{l}
\displaystyle E\text{-isoeugenol:}\quad \ce{\underset{(1)}{HO}-\text{Ar}-CH{=}\!\!CHCH_3} \[1mm]
\displaystyle Z\text{-isoeugenol:}\quad \ce{\underset{(1)}{HO}-\text{Ar}-CH{=}\!\!CHCH_3} 
\end{array}
$$

---

Here “Ar” stands for the benzene ring which is substituted with $$\ce{-OCH_3}$$ at C2. The difference between the two isomers is the relative position of the substituents around the $$\ce{C=C}$$ double bond in the side‐chain:

• In the $$\displaystyle E$$–isomer the aromatic (large) group and the methyl group are on opposite sides of the double bond.

• In the $$\displaystyle Z$$–isomer the aromatic group and the methyl group are on the same side of the double bond.

A skeletal diagram for each is shown below.

---

**$$E$$–isoeugenol**

$$
\begin{array}{ccccccc}
 & & \overset{\displaystyle OCH_3}{\vert} & & & & \
 & & \bullet & & & & \
HO & - & \underset{\text{benzene ring}}{\ce{C_6H_3}} & - & \,C(=) & CH & CH_3 \
 & & & & \ \rotatebox{180}{$$ \longleftrightarrow $$} & & \
 & & & & \text{(trans)} & & 
\end{array}
$$

In this depiction the double bond in the propenyl side chain is drawn so that the aromatic ring and the $$\ce{CH_3}$$ group lie on opposite sides.

---

**$$Z$$–isoeugenol**

$$
\begin{array}{ccccccc}
 & & \overset{\displaystyle OCH_3}{\vert} & & & & \
 & & \bullet & & & & \
HO & - & \underset{\text{benzene ring}}{\ce{C_6H_3}} & - & \,C(=) & CH & CH_3 \
 & & & & \ \rotatebox{180}{$$ \longleftrightarrow $$} & & \
 & & & & \text{(cis)} & & 
\end{array}
$$

Here the double bond is drawn so that the aromatic ring substituent and the methyl group are on the same side of the double bond.

---

Each diagram should be interpreted with the benzene ring drawn in the plane. To be precise, label the substituents on the ring as follows:

- C1: $$\ce{-OH}$$  
- C2: $$\ce{-OCH_3}$$  
- C4: $$\ce{-CH=CHCH_3}$$

Thus, the complete structures are:

$$
\begin{array}{rcl}
\textbf{$$E$$-isomer:} & \text{4-(1-propenyl)-2-methoxyphenol with trans-configuration about the } \ce{C=C} \text{ bond,} \
\[1mm]
\textbf{$$Z$$-isomer:} & \text{4-(1-propenyl)-2-methoxyphenol with cis-configuration about the } \ce{C=C} \text{ bond.}
\end{array}
$$

These are the two stereoisomers of compound Y.
The two stereoisomers of compound Y are: 1. **E-isoeugenol**: The aromatic group and the methyl group are on opposite sides of the double bond. 2. **Z-isoeugenol**: The aromatic group and the methyl group are on the same side of the double bond. These structures are: $$ \begin{array}{rcl} \textbf{E-isomer:} & \text{4-(1-propenyl)-2-methoxyphenol with trans-configuration,} \ \textbf{Z-isomer:} & \text{4-(1-propenyl)-2-methoxyphenol with cis-configuration.} \end{array} $$

(b) Compound Y is a naturally occurring vanilloid found in the oil of the ylang-ylang plant. It has a molecular formula \( \mathrm{C}_{10} \mathrm{H}_{12} \mathrm{O}_{2} \) and has stereoisomers. Draw and label the structures of the stercoisomers of compound Y . modificd 2013/11/3

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