What does orthogonal mean for a pair of protecting groups?

• Both remove in the same single wash
• Each removes under conditions leaving the other untouched
• Neither group can ever be removed

Why do chemists mask carbonyls as acetals?

• To make them react faster with every reagent
• To protect them through harsh steps, then unmask with aqueous acid
• To turn them into better leaving groups for later substitution steps

A capped ether behaves exactly like a free hydroxyl toward strong reagents.

A deprotection uses strong base. What must you check first?

• Which other groups in the molecule would not survive it
• Whether the solvent is perfectly dry
• The color of the reaction mixture

Two hydroxyls must free at different points. One mask frees with hydrogen, the other with acid, and each recipe was checked to leave the other mask untouched. Which pair do you pick?

• Two identical acid labile masks stripped together in one wash
• Two identical masks stripped by hydrogen
• One mask stripped by hydrogen and one stripped by acid

A route runs neutral and mild non-aqueous acid steps, with aqueous base plus acidic workup available at the end. When does a methyl ester serve well as the masked acid?

• When you want a mask that no condition can ever open
• When every step of the route is strongly acidic and aqueous
• When the mask stands mild acid steps, then opens with base

A colleague proposes global deprotection to save three steps. The plan sacrifices one ester the target requires, and no restoration step is planned. How do you decide?

• Always refuse global steps on principle alone without ever counting
• Refuse: the target needs that ester and no restore is planned
• Always take the global wash since fewer steps always win

A route strips an acid labile ether while a needed acetal sits nearby. What is the risk?

• The acetal may also fall, since acid unmasks it too
• Acetals always survive any acid wash
• Ethers can never be removed selectively under any conditions