Lewis acid-base definition identifying

The spectra obtained from the chemisorption of methanol onto catalyst above 100°C indicated the progressive oxidation of methoxy species to formate via dioxymethylene/HCHO and finally to CO, CO2, and H2. Phenol adsorbed on the surface Lewis acid-base pair site and dissociated to phenolate anion and proton. The formation of phenolate anion and proton were discerned from the strong intense C-0 stretching vibration and the disappearence of phenolic 0-H stretching vibration, respectively. Importantly, there were series of definite low intensity bands between 2050 and 1780 cm" that were identified as the out-of-plane aromatic C-H bending vibrations [79, 84-85]. These bending vibrations are possible only if the phenyl ring of phenol is perpendicular to the catalyst surface. 

For each of the following reactions identify the acid and the base. Also indicate which acid-base definition (Lewis, solvent system, Brpnsted) applies. In some cases, more than one definition may apply. 

You have reviewed the Bronsted-Lowry definition of acids and bases and the meanings of pH and pTQ. You have learned to identify the most acidic hydrogen atoms in a molecule based on a comparison of pIQ values. You will see in many cases that Brensted—Lowry acid-base reactions either initiate or complete an organic reaction, or prepare an organic molecule for further reaction. The Lewis definition of acids and bases may have been new to you. However, you will see over and over again that Lewis acid—base reactions which involve either the donation of an electron pair to form a new covalent bond or the departure of an electron pair to break a covalent bond are central steps in many organic reactions. The vast majority of organic reactions you will study are either Bronsted-Lowry or Lewis acid—base reactions. 

If the acid-base reaction is written with the electron pairs and the arrows, as shown for water and HCl, the Lewis base definition is quite useful. The electron-rich molecule is the base, and the electron-rich atom donates two electrons. The molecule bearing the electron-deficient atom (hydrogen) is the acid. For reactions of organic molecules, it is essential to identify electron-rich and electron-poor components of molecules, to understand the electron flow, and to understand how to predict the products. That process begins with making the transition to thinking in terms of Lewis bases/Lewis acids rather than Br0nsted-Lowry acids and bases. 

In practice, it s much simpler to use the Arrhenius or Bronsted-Lowry definition of acid and base, but you ll need to use the Lewis definition when hydrogen ions aren t being exchanged. You can pick and choose among the definitions when you re asked to identify the acid and base in a reaction. 

Draw Lewis structures (electron-dot formulas) for all the substances in the reaction equation, identify each reactant as a Br0nsted acid or base, and then propose a definition for an acid and a base based on the ability of the substance to accept or donate a pair of electrons to form a covalent bond. 

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