Explain the concept 'hierarchy of controls'. 2. (6 pt) A safety-conscious student decided to apply the concept of 'substitution for the preparation of Grigard reagent. He replaced diethyl ether with MTBE but unfortunately the reaction didn't work. a. Why is MTBE safer than diethyl ether? b. What is the reason that the reaction didn't work? Think what is the role of ether in this reaction and the differences between the two ethers. Would tetrahydrofuran work? 3. (4 pt) Why the carbocation is colored? Draw a scheme to demonstrate your explanation.