Part 6: MECHANISM

The following diagram shows the solution to the mechanistic question. Note that all the information applies to a single reaction sequence that has been completely described verbally.  There is no need for extra reagents or extra steps etc. The curly arrows are drawn specifically to match the text in the question. The biggest problem students have is making sure they understand the language of chemistry. Most students have trouble because they can't draw the structures from the IUPAC names (that means they don't know their nomenclature well enough). Read the words carefully, and then make the curly arrows tell that same story. There is NO need for extra steps. Remember curly arrows go from electron rich to poor and to balance the formal charges at each step - errors on formal charges were common.

a. work in progress

b. Sodium bicarbonate, NaHCO₃ or sodium carbonate, Na₂CO₃, or pyridine would be good choices. Note that the question requires pKa < 12 so HO- or RO- aren't acceptable answers.

c. Benzoic acid, methyl iodide and triethyl amine.

d. Phenol, methyl iodide and an alkoxide (e.g. NaOH, NaOCH₃ or NaOCH₂CH₃). Note that you need a stronger base that an a simple amine because the phenol is not as acidic as the carboxylic acid (see below).

e. Phenol is less acidic than a carboxylic acid. Both conjugate bases are stabilised by resonance, but in the carboxylic acid, the resonance allows the -ve charge to be delocalised to a second electronagative oxygen atom while in the phenol, the delocalisation is to carbons atoms. The oxygen better stablises the -ve charge due to its electronegativity.

Common errors: