Arrow Notations, Electrophile and Nucleophiles
Before you explore the specific mechanism, there are some important terms you need to understand which are shown in the links provided below:
1. (a) Follow this link for helpful advice on how to draw curly arrows when describing organic reaction mechanisms. Curly Arrows
2. (a) Definitions of electrophile and nucleophile.
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Electrophile: An electron deficient atom, ion or molecule that has an affinity for an electron pair, and will bond to a base or nucleophile. It is something which is attracted to electron-rich regions in other molecules or ions. Because it is attracted to a negative region, an electrophile must be something which carries either a full positive charge, or has a slight positive charge on it somewhere. Eg. of electrophiles: cations such as H+ and NO+, HCl, alkyl halides(CH3Cl),acyl halides, and carbonyl compounds, Cl2 and Br2, and some lewis acids such as BH3 , AlCl3 and carbocations (or called carbonium ions). Nucleophile: An atom, ion or molecule that has an electron pair that may be donated in bonding to an electrophile (or Lewis acid). It is a species (an ion or a molecule) which is strongly attracted to a region of positive charge in something else. Nucleophiles are either fully negative ions, or else have a strongly delta negative charge somewhere on a molecule. Common nucleophiles are hydroxide ions, cyanide ions, water, ammonia |
The importance of electrophile / nucleophile terminology comes from the fact that many organic reactions involve at some stage the bonding of a nucleophile to an electrophile, a process that generally leads to a stable intermediate or product.
(b) Electrophile and Nucleophile (The video below gives an interesting explanation of the two terms. )
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Organic Chemistry Nucleophile and Electrophile.flv Size : 4.325 Kb Type : flv |
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Organic Chemistry Lewis Acids.flv Size : 1.574 Kb Type : flv |