Double-Substitution Reactions

Double Substitution or Double-Replacement Reactions. Double substitution or double-replacement reactions (also called double-decomposition or metathesis reactions) involve two ionic compounds, most often in aqueous solution. In this type of reaction, the cations simply swap anions. The reaction proceeds if a solid or a covalent compound is formed from ions in solution. All gases at room temperature are covalent. Some reactions of ionic sohds plus ions in solution also occur. Otherwise no reaction takes place. 

Hydroboration is highly regioselective and stereospecific. The boron becomes bonded primarily to the less-substituted carbon atom of the alkene. A combination of steric and electronic effects works to favor this orientation. Borane is an electrophilic reagent. The reaction with substituted styrenes exhibits a weakly negative p value (-0.5).156 Compared with bromination (p+ = -4.3),157 this is a small substituent effect, but it does favor addition of the electrophilic boron at the less-substituted end of the double bond. In contrast to the case of addition of protic acids to alkenes, it is the boron, not the hydrogen, that is the more electrophilic atom. This electronic effect is reinforced by steric factors. Hydroboration is usually done under conditions in which the borane eventually reacts with three alkene molecules to give a trialkylborane. The... 

To simplify the discussion, we will classify simple chemical reactions into five types Type 1 combination reactions Type 2 decomposition reactions Type 3 substitution reactions Type 4 double-substitution reactions Type 5 combustion reactions... 

If a double-substitution reaction took place, NaNO, and KCl would be produced. However, both of these are soluble and ionic hence, there is no driving force and therefore no reaction. 

As substrates, pyrrolotetrazoles 12 and 13 have been used in a variety of electrophilic substitutions. It has been observed that with the exception of bromination, monosubstitution (acetylation, benzoylation, carbamoylation, formylation, azo coupling, nitrosation, and reaction with dimethyl acetylenedicarboxylate (DMAD)) occurs preferentially at C-5, if the 5- and 7-positions are both available. Upon bromination, double substitution occurs at C-5 and C-7 with the same substrates. It has further been observed that substitution at C-7 occurs only if C-5 is occupied <2001J(P1)729>. 

This obstacle can be overcome by moving electron withdrawing substituents away from the double bond and increasing the reactivity of double bond by positioning it in a strained ring. This is achieved using bicyclic monomers. The monomers are readily obtained from the Diels-Alder reactions of substituted olefins with cyclopentadiene. This route is effective also for fluorinated monomers. These types of monomers undergo a ROMP with a variety of one component and two-component initiator systems. 

The coupling reaction of allylsilane with the w-thiomethoxyacetal is catalyzed by TMSOTf51. TiCLj-mediated reaction of a-bromoallylsilane 7 with 1,1-diethoxyethane leads to homoallylic ether 12 stereoselectively in excellent yield (equation 9)40. Under similar reaction conditions, double substitution of allylsilane to diketals 13 affords 14 in high diastereoselectivity (equation 10)52. 

The desymmetrization of dicarbonate 206 was initiated by the addition of one equivalent of N-(3-butenyl) nosylamide 207 under palladium catalysis in the presence of Trost s chiral diphosphine ligand 205. When the first allylic substitution was completed, the reaction was warmed and the resulting intermediate 208 was treated in situ with one equivalent of a second nosylamide 209. Product 210 resulting from this double substitution reaction was submitted to a tandem intramolecular ROM/RCM to furnish key precursor 211, which was engaged in the final cyc-lization step by the reduction of the double bonds, followed by the HCl-promoted domino deprotection of the acetal and aminal formation. 

To create target inhibitors with more flexible side chains and reduced molecular weights we attached protected aminopentane tethers to both hydroxy groups of scaffold 1, via double substitution reaction, leading to the formation of ether... 

Fukui functions and local softnesses and their application in typical organic reactions (electrophilic substitutions on aromatic systems, nucleophilic additions to activated carbon-carbon double and triple bonds) [34-39]. 

Starting from the same reagents, one can also effect a double substitution on the aromatic ring (Figure 1.24, left). However, the mechanism is completely different (Figure 5.13 and following figures). This substitution takes place under reaction conditions in which no radical intermediates are formed. (Further discussion of this process will be presented in Section 5.2.1.)... 

This is a second-order reaction because methoxide ion is a strong base as well as a strong nucleophile. It attacks the alkyl halide faster than the halide can ionize to give a first-order reaction. No substitution product (methyl tert-butyl ether) is observed, however. The SN2 mechanism is blocked because the tertiary alkyl halide is too hindered. The observed product is 2-methylpropene, resulting from elimination of HBr and formation of a double bond. 

A certain double substitution reaction produced silver chloride and potassium scetate. What were the reactants ... 

Can a double substitution reaction occur between two compounds containing one bn in common ... 

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