Organic Chemistry for the Chemistry Olympiad — Practice

Question 1

Find the degrees of unsaturation of C6H6.

Accepted Answer

(2 x 6 + 2 - 6)/2 = 4.

Question 2

Is a nitro group ortho, para or meta directing in electrophilic aromatic substitution?

Accepted Answer

Meta directing, and deactivating.

Question 3

How many stereoisomers does 2,3-dibromobutane have?

Accepted Answer

Three: a pair of enantiomers (R,R) and (S,S), and the meso (R,S) form. Two stereocentres allow four, but the meso form is a duplicate.

Question 4

Describe the proton NMR of ethanol.

Accepted Answer

A triplet of 3H for CH3, a quartet of 2H for CH2 and a singlet of 1H for OH, from the n + 1 rule.

Question 5

Compare the stereochemical outcome of SN1 and SN2 at a chiral carbon.

Accepted Answer

SN2 gives inversion of configuration. SN1 gives racemisation because the planar carbocation is attacked from both faces.

Question 6

Explain why a carboxylic acid is far stronger than an alcohol.

Accepted Answer

The carboxylate ion delocalises its negative charge over two oxygens by resonance, stabilising the conjugate base. An alkoxide's charge is localised on one oxygen.

Question 7

A compound C3H6O shows a strong IR band near 1715 per cm and a single NMR singlet of 6H. Identify it.

Accepted Answer

Acetone, CH3COCH3. One degree of unsaturation fits the C=O at about 1700 per cm and all six hydrogens are equivalent.

Question 8

Which carbonyl compounds undergo the Cannizzaro reaction?

Accepted Answer

Aldehydes with no alpha hydrogens, in strong base.

Practice — Organic Chemistry for the Chemistry Olympiad

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