Isomerism: Optical (CIE A Level Chemistry)

This question is about the chemistry of limonene.

Limonene is commonly found in the rinds of citrus fruits such as grapefruit, lemon, lime and oranges. It is a naturally occurring hydrocarbon with the molecular formula C₁₀H₁₆.

Limonene exists as a pair of enantiomers:

• One enantiomer is responsible for a strong orange smell
• The other enantiomer is responsible for a lemon smell.

Draw 3D representations of the two enantiomers of limonene.

Suggest why receptors in the human nose can distinguish between the orange and lemon enantiomers of limonene.

Limonene can undergo full hydrogenation to form menthane as shown.

For the complete hydrogenation of an impure sample of 3.00 g of limonene at room temperature and pressure, 870 cm³ of hydrogen was required. 

Calculate the percentage purity of limonene.

(1 mol of hydrogen occupies 24.0 dm³ at room temperature and pressure)

percentage purity = ........................ %

The final step of the multi-step synthetic conversion of limonene to menthol is shown.

 

State the reagent for this reaction and the type of reaction.

Leucine is an optically active amino acid with the molecular formula (CH₃)₂CHCH₂CH(NH₂)COOH. 

Draw the displayed formula of leucine.

Leucine exists as stereoisomers. 

The two optical isomers of leucine taste different. One isomer has a bitter taste, the other is sweet.

Draw the three-dimensional arrangement of the two optical isomers.

Give the IUPAC name of leucine.