lewis_acid_and_bases - Lewis Acids Lewis Bases...

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Lewis Acids, Lewis Bases, Electrophiles, and Nucleophiles Chemical reactions originate from the flow of electrons from an electron source to an electron sink. An important skill that aids one in predicating the outcome of chemical reactions is the ability to identify which species can act as an electron source an which can act as an electron sink. By definition, a Lewis base is an electron pair donor, and thus acts as a source of electrons. A Lewis acid is electron pair acceptor, and thus acts as an electron sink. When a Lewis base donates a pair of electrons to a carbon atom, it is further described as a “nucleophile”, which means nucleus loving. The nucleus is the positive part of an atom, thus something that is electron rich would seek, or “love” the nucleus, hence the name nucleophile. Conversely, an electrophile is electron “loving” species because it is electron deficient. When a carbon atom accepts a pair of electrons, it is called an electrophile. Electron source = Lewis base Electron sink = Lewis acid Lewis Acids: I. Strong Lewis Acids A. Neutral compounds containing group III elements: BF 3 , BH 3 , AlCl 3 Group III elements cannot have a filled octet without having a formal charge of –1. Thus, neutral boron and aluminum compounds have an empty p-orbital that can accept a pair of electrons. B. Carbocations: CH 3 + , (CH 3 ) 3 C + , etc. Similar to the group III elements involved in three covalent bonds, carbocations also have an empty p-orbital. Since they are in group IV, having just three bonds (an no lone pair electrons) results in a formal charge of +1 on the carbon (in addition to the empty orbital).
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lewis_acid_and_bases - Lewis Acids Lewis Bases...

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