Electrophilic Addition Reaction
Electrophilic addition is a type of chemical reaction in which an electrophile (an electron-deficient species) reacts with a nucleophile (an electron-rich species) to form a new molecule. This reaction is commonly observed in organic chemistry, particularly in the addition of unsaturated hydrocarbons like alkenes and alkynes. The process involves the breaking of pi bonds and the formation of new sigma bonds.
3 Key excerpts on "Electrophilic Addition Reaction"
eBook - ePub- J Fisher, J.R.P. Arnold, Julie Fisher, John Arnold(Authors)
- 2020(Publication Date)
- Taylor & Francis(Publisher)
...There are two general classes of addition reaction that may be considered, nucleophilic and electrophilic addition (Section I1). For either type of addition reaction to occur one or more units of unsaturation must be present in the molecule being added to. Consequently, addition reactions are only possible with, for example, alkenes, alkynes, aldehydes, and ketones. Addition reactions are not generally feasible with aromatic compounds as they would result in the loss of aromaticity, a stabilizing force (Section K1). An example of an Electrophilic Addition Reaction is offered by the production of alcohols from alkenes; In a similar manner mono- or dihalogenated compounds may be formed; The reactions are termed electrophilic as the carbon-carbon double bond is electron rich and therefore attractive to the electrophile (OH 2 or BrH) (Section I1). Following the addition of an atom or group to one end of the multiple bond, a positive charge is set up at the other end making this susceptible to nucleophilic attack. Nucleophilic addition is common with carbonyl compounds (Section J2) in which the carbonyl carbon is electrophilic and the carbonyl oxygen nucleophilic. Carbon is a better electrophile than oxygen is a nucleophile, and therefore nucleophilic addition is the favored reaction. An example of nucleophilic addition is provided by the production of a cyanohydrin from a ketone and hydrogen cyanide; Substitution reactions Substitution reactions are said to have occurred when an atom or group on a molecule is replaced by an atom or group on another. As with addition reactions these may be both nucleophilic and electrophilic; the former being characteristic of alkyl halides, carboxylic acids, and derivatives thereof, the latter characteristic of aromatic compounds. Nucleophilic substitution reactions involving alkyl halides are generally subdivided in terms of the molecularity of the rate determining step for the reaction (Section P3)...
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...The reaction is useful in the protection or purification of alkenes or as a means of synthesizing alkynes. The halogen molecule is polarized as it approaches the alkene double bond thus generating the required electrophilic center. The intermediate formed is called a bromonium ion intermediate in the case of bromine and is stabilized since it is possible to share or delocalize the positive charge between three atoms. If the reaction is carried out in water, water can act as a nucleophile and intercept the reaction intermediate to form a halohydrin where a halogen atom is added to one end of the double bond and a hydroxyl group is added to the other. Alkenes to alcohols Alkenes can be converted to alcohols by treatment with aqueous acid (e.g. sulfuric acid). Milder conditions can be used with mercuric acetate to produce an organomercury intermediate which is reduced with sodium borohydride. Alkenes to ethers A similar reaction to the mercuric acetate/sodium borohydride synthesis of alcohols allows the conversion of alkenes to ethers. In this case, mercuric trifluoracetate is used. Alkenes to arylalkanes Alkenes can be reacted with aromatic rings to give arylalkanes. The reaction is known as a Friedel–Crafts alkylation of the aromatic ring but can also be viewed as another example of an electrophilic addition to an alkene. Related topics (E4) Organic structures (H4) Electrophilic addition to unsymmetrical alkenes (H5) Carbocation stabilization (H7) Hydroboration of alkenes (I3) Electrophilic substitutions of benzene Reactions Many of the reactions which alkenes undergo take place by a mechanism known as electrophilic addition (Figure 1). In these reactions, the π bond of the double bond has been used to form a bond to an incoming electrophile and is no longer present in the product. Furthermore, a new substituent has been added to each of the carbon atoms. Figure 1...
eBook - ePubBiochemistry
An Organic Chemistry Approach
- Michael B. Smith(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...The fundamentals of both acyl addition and of acyl substitution reactions will be presented for carbonyl electrophilic centers and the reactions of these electrophilic centers with nucleophiles. 3.1 Nucleophiles and Bimolecular Substitution (the S N 2 Reaction) The S N 2 reaction is one of the seminal reactions in a typical undergraduate organic chemistry course. The reaction of 1-bromo-3-methylbutane with sodium iodide (NaI) using acetone as a solvent gave 1-iodo-3-methylbutane, in 66% yield. 1 In terms of the structural changes, the iodide ion substitutes for the bromine, producing bromide ion (Br –). Iodide reacted as a nucleophile in the reaction at C δ+ of the alkyl bromide, breaking the C—Br bond and transferring the electrons in that bond to bromine. In molecules that contain the C—Br bond, or indeed a C—C bond, where X is a heteroatom-containing group, the carbon will have a δ + dipole. In other words, the carbon atom is electrophilic, and the substrate that reacts with the nucleophile is called an electrophile. The reaction of a nucleophile with an aliphatic electrophile is formally called nucleophilic aliphatic substitution, illustrated in Figure 3.1. The displaced atom or group (e.g., chloride), departs (leaves) to become an independent ion. Displacement of chlorine leads to the chloride ion (Cl –), but the bromide ion, iodide ion, or a sulfonate anion also correlates to X, which is referred to as a leaving group. In many biochemical reactions, the leaving group is a phosphate, —O–PO 2 –O—. 1 Furniss, B.S.; Hannaford, A.J.; Smith, P.W.G.; Tatchell, A.R. (eds.), Vogel’s Textbook of Practical Organic Chemistry, 5th ed. Longman, Essex, UK, 1994, Exp. 5.62, p. 572. FIGURE 3.1 Nucleophilic attack at a sp 3 carbon bearing a leaving group. A leaving group does not spontaneously “fly off” or “leave,” it is displaced by the nucleophile after collision with the electrophilic carbon atom...
