The structure of the compound γ-ionone is shown.
Including γ-ionone, how many stereoisomers exist with this molecular formula?
Correct Answer: \( \boxed{\mathrm{C}} \)
The molecule contains:
Therefore, the total number of stereoisomers is:
\(\mathrm{2\times2=4}\)
Therefore, the correct answer is (C).
The structure of disodium cromoglycate is shown.
How many chiral centres are there in this molecule?
Correct Answer: \( \boxed{\mathrm{A}} \)
A chiral centre is a carbon atom bonded to four different groups.
The central carbon is bonded to two identical \(\mathrm{-CH_2O-}\) groups, so it is not chiral.
All other carbon atoms are either part of aromatic rings or carbonyl groups and cannot be chiral centres.
Therefore, the molecule contains no chiral centres, so the correct answer is (A).
Some properties of compound X are listed.
What are the possible identities of X?
Correct Answer: \( \boxed{\mathrm{B}} \)
For complete combustion of a compound \(\mathrm{C_xH_yO_z}\),
\(\mathrm{O_2\ required}=x+\dfrac{y}{4}-\dfrac{z}{2}\)
The required oxygen is \(8.5\,\mathrm{mol}\), which matches compounds with the molecular formula \(\mathrm{C_6H_{12}O}\):
\(6+\dfrac{12}{4}-\dfrac{1}{2}=8.5\)
Compound 2 is a tertiary alcohol and compound 4 is a ketone. Neither is oxidised by hot acidified \(\mathrm{KMnO_4}\).
Compound 1 is a primary alcohol and compound 3 is a tertiary alcohol with a different molecular formula, so they do not satisfy both conditions.
Therefore, the possible identities of X are 2 and 4, so the correct answer is (B).
