Home / AS & A Level Chemistry 13.3 Shapes of organic molecules Exam Style Practice Questions Paper 1
Two statements about a molecule of methanal are given.
1 It is planar.
2 It contains three \(\sigma\) bonds.
Which statements are correct?
Correct Answer: \( \boxed{\mathrm{A}} \)
Methanal, \(\mathrm{HCHO}\), has an sp\(^2\)-hybridised carbon atom, giving a trigonal planar arrangement around the carbon atom.
It contains two \(\mathrm{C-H}\) single bonds and one \(\mathrm{C=O}\) double bond.
A double bond consists of one \(\sigma\) bond and one \(\pi\) bond, so methanal contains:
Therefore, methanal has three \(\sigma\) bonds and is planar.
Therefore, the correct answer is (A).
The skeletal formulae of two compounds are shown.
Which statements about progesterone and testosterone are correct?
Correct Answer: \( \boxed{\mathrm{D}} \)
Both progesterone and testosterone contain a ketone (\(\mathrm{C=O}\)) functional group.
The carbon-carbon double bond is within the fused ring system, so it does not give rise to geometrical (E/Z) isomerism.
Testosterone contains an alcohol (\(\mathrm{-OH}\)) group, whereas progesterone contains an additional ketone group. Therefore, they do not have the same molecular formula.
The two compounds have the same steroid carbon skeleton and the same number of chiral carbon atoms.
Therefore, the correct answer is (D).
Quinone is an unsaturated molecule.
Which statement about quinone is correct?
Correct Answer: \( \boxed{\mathrm{D}} \)
Quinone consists of a conjugated six-membered ring in which all ring atoms are \(\mathrm{sp^2}\)-hybridised.
Therefore, the molecule is planar.
Although each carbonyl (\(\mathrm{C=O}\)) bond is polar, the molecule is highly symmetrical. The dipole moments of the two carbonyl groups are equal and opposite, so they cancel each other.
Hence, quinone has no overall dipole moment.
Therefore, the correct answer is (D).