Which cannot be used in a Claisen condensation?

In the presence of strong acids, which of the oxygen atoms on the carboxyl group is preferentially protonated and why?

Which of the following two amides will react more readily with a nucleophile? Why?

Bonus question Identify the compound (C4H6O2) that gives the following 1H NMR spectrum.

Bonus question Reaction of butanenitrile with CH3MgBr  followed by treatment with aqueous  acid, forms G compound. G has a molecular ion in its mass spectrum at m/z= 86 and a base peak at m/z= 43. G exhibits a strong absorption in its IR spectrum  at 1721 cm-1 and has the 1H NMR spectrum given below. What is the IUPAC name of the structure that represents  G compound?  

Predict the product when cyclohexanone reacts with aqueous sodium hydroxide at 100°C.   

What is the cyclic product formed in the intramolecular Aldol condensation when the following compound is treated with aqueous NaOH?

Predict the product(s) for the following reaction.    

What is the product of the following reaction?  

Which of the following structures is the major contributor to the resonance hybrid of the phenoxide anion?