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Which of the following statements is correct regarding camphor which is illustrated below? (image: Wikipedia)
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Correct Answer: D. Camphor has two stereogenic centers and exists as a pair of enantiomers.
Position 1 and 4 as labeled in the diagram below (Ref: csi.chemie.tu-darmstadt.de) are the only 2 chiral (stereogenic) carbons in camphor since they are attached to 4 different substituents, each. Notice that because of the carbonyl group being closer to position 1, and because of the methyl substituent at position 1, the molecule is NOT symmetric when looking at it from above. Because a line of symmetry cannot be drawn, thus the molecule is NOT meso, and thus it has 2 non superposable (= non superimposable) mirror images (= enantiomers).
Additional learning points: Note that the maximum number of stereoisomers is given by 2 to the power of n, where n is equal to the number of chiral carbons. So the maximum for camphor, having 2 chiral carbons, would be 2 squared which is 4. However, camphor yields only two stereoisomers because the relative configuration of both centers is constrained in the bicyclic ring system (i.e. 2 closed rings in one system).
Also, note this Mnemonic: MeSo = Mirror of Symmetry.
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