Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Are these compounds chiral ? Draw diagrams to justify your answer.
(1) 
(2) 
(3) 
(4) 
(5) 
Options:
Answer:
Solution:
Ans. Compounds (2), (4) and (5) are chiral; (1) and (3) are not.
Sol. Purpose of the problem : reinforcement of the very important criterion for chirality.
Only one thing matters - does the molecule have a plane of symmetry ? We need to redraw some of them to see if they do. Do not look for chiral centres (carbon atoms with four different groups) - just look for a plane of symmetry (POS).
(1) NOT chiral. The molecule has a plane of symmetry passing through the C(OH)2 carbon and the opposite C-C bond; the two halves (each carrying CO2H) are mirror images.
(2) CHIRAL. This is a spiro compound: the two rings are joined at a tetrahedral carbon atom and are orthogonal, so there is no plane of symmetry.
(3) NOT chiral. The adamantanol cage has a plane of symmetry running vertically through the C-OH bond and the opposite bond.
(4) CHIRAL. A bit of a trick: it has to be redrawn to check, and then you notice that the two naphthalene rings are joined at different positions (one through its 1-position, the other through its 2-position). The only possible plane of symmetry is not a plane of symmetry, so the molecule is chiral.
(5) CHIRAL. The CO2H group is on a tetrahedral centre, so the ring itself is not a plane of symmetry; the exocyclic alkene puts the phenyl group on one side and a hydrogen on the other, so the plane at right angles to the ring is not a plane of symmetry either.
