Basicity nucleophilicity difference

To summarize in contrast to the observed nucleophilic attack of strongly basic nucleophiles on the sulfonyl and sulfoxy sulfur of the three-membered ring sulfones and sulfoxides, the acyclic sulfone and sulfoxide groups are attacked by nucleophiles only with difficulty Although the precise reason for this difference is as yet not clear, it is most probably associated with the geometry, electronic structure, bonding and strain energy of the cyclic compounds. 

The behavior of the different amines depends on at least four factors basicity, nucleophilicity, steric hindrance and solvation. In the literature (16), 126 aliphatic and aromatic amines have been classified by a statistical analysis of the data for the following parameters molar mass (mm), refractive index (nD), density (d), boiling point (bp), molar volume, and pKa. On such a premise, a Cartesian co-ordinate graph places the amines in four quadrants (16). In our preliminary tests, amines representative of each quadrant have been investigated, and chosen by consideration of their toxicity, commercial availability and price (Table 1). 

The equilibrium of nucleophilic displacements favors the side with the weaker Bronsted base the stronger Bronsted base displaces the weaker Bronsted base. The rate of the displacement reaction on the C of a given substrate depends on the nucleophilicity of the attacking base. Basicity and nucleophilicity differ as shown ... 

Simple orbital interaction theory is only partially informative in distinguishing the relative basicities (nucleophilicities) of carbonyl groups in different bonding environments,... 

The demonstration that the mechanism of catalysis may change to general base catalysis for weakly basic nucleophiles further complicates the interpretation of such plots. The most useful generalizations that can be extracted from the data for aryl acetates are illustrated in Fig. 18. This is a plot of data for the reactions of oxyanions with three esters, phenyl, 4-nitrophenyl, and 2,4-dinitrophenyl acetates under the same conditions. Only nucleophiles showing normal reactivity are included points for hydro, de ion and a-effect nucleophiles have been excluded. The data are those of Jencks and Gilchrist283, who published a slightly different version of this plot. 

Now- we can understand this difference between nucleophilicity and basicity. Nucleophilicity measures how fast things happen, which is called kinetics. Basicity measures stability and the position of equilibrium, which is called thermodynamics. Throughout your course, you will see many reactions where the product is determined by kinetic concepts, and you will also see many reactions where the product is determined by thermodynamic concepts. In fact, there will even be times, where these two factors are competing with each other and you will need to make a choice of which factor wins kinetics or thermodynamics. 

Basically, two different routes are conceivable for their asymmetric construction 1) nucleophilic substitution reaction with a fluoride anion and 2) electrophilic addition of fluoronium cations to activated or masked carbanions. First attempts on enantioselective nucleophilic fluorination date back to the pioneering work of Hann and Sampson [3]. In an ambitious dehydroxylation/fluorination sequence the authors reacted a racemic a-trimethylsiloxy ester with a half molar equivalent of an enantiomerically pure proline-derived aminofluorosulphurane in hope to achieve a kinetic resolution. Unfortunately, the fluorinated product was obtained without significant enantiomeric excess. 

SN1 versus S There are two different mechanisms involved in the nucleophilic substitution of alkyl halides. When polar aprotic solvents are used, the SN2 mechanism is preferred. Primary alkyl halides react more quickly than secondary alkyl halides, with tertiary alkyl halides hardly reacting at all. Under protic solvent conditions with non-basic nucleophiles (e.g. dissolving the alkyl halide in water or alcohol), the SN1 mechanism is preferred and the order of reactivity is reversed. Tertiary alkyl halides are more reactive than secondary alkyl halides and primary alkyl halides do not react at all. 

Throughout this book, and in association with the various reactions presented, various reagents were presented that, due to their specific properties, react in very specific ways. These reagents differ in their basicity, nucleophilicity, and preferred sites of reaction. Table 8.1 summarizes the various properties of the reagent classes presented. 

The ketones and aldehydes have basically two different sites where a reaction with a nucleophile can take place the carbon of the carbonyl group and the hydrogen atom bonded to the a carbon.1,4 If a nucleophile reacts with the carbon of the carbonyl group several products can be formed.1,4 For instance, if the nucleophile is a hydride anion, a reduction of the double bond occurs.52 If a base reacts with the hydrogen atom bonded to the a carbon, the result is an enolate anion.53 Figure 17 summarizes these possibilities. 

Skoog and Jencks initially investigated the rates of transfer of the phosphoryl group from phosphorylated 3-methoxypyridine to a variety of substituted pyri-dines and amines that differ in pK and concluded that free metaphosphate anion is not involved as an intermediate (50). The basis for this experiment is the expectation that if metaphosphate anion is a true intermediate, a change in the rate-determining step should occur as the basicity of the acceptor pyridine or amine is varied. When the acceptor is less basic (nucleophilic) than 3-... 

Sometimes basic conditions are specified, but there aren t any acidic protons. You might want to look for protons that are three bonds away from a leaving group X, e.g., H—C—C—X. If there are good nucleophiles present, then you may also need to look for electrophilic atoms. Don t forget that heteroatoms that have their octet and that bear a formal positive charge are not electrophilic Typical nucleophiles differ under basic and acidic conditions. 

A very important difference between elimination and substitution is their emphasis on nucleophilicity and basicity. Nucleophilicity is the affinity of a base for a carbon atom in a displacement reaction transition state. 

Ease of Use and User Friendliness. CAMEO was found to be easy to use. CAMEO S menu screens are well designed and easy to follow, and greatly facilitate use and operation of the program, particularly structure entry. To explore fully all potential reactions and the products of these reactions, however, the user must separately evaluate a given set of starting materials and reaction conditions under several if not all of the available reaction modules (i.e., Carbenoid, Radical, Heterocyclic, Basic/Nucleophilic, Acidic/Electrophilic, Electrophilic Aromatic, Oxidative/Reductive, and Pericyclic). Thus, the user can enter reactants and reaction conditions, and, depending upon which module is selected, CAMEO may predict different results. For example, CAMEO correctly predicted carbaryl as the product from the reaction of methyl isocyanate with 1-naphthol only if the Acidic/Electrophilic mechanistic module was selected no product was predicted when the Basic/Nucleophilic module was selected. 1-Naphthol is clearly the nucleophile in this reaction, and it seems that CAMEO should have recognized it as such. 

This observation is very significant. The fact that the nucleophile does not appear in the rate equation means that not only does its concentration not matter—its reactivity doesn t matter either We are wasting our time opening a tub of NaOH to add to this reaction—water will do just as well. All the oxygen nucleophiles in the table above react at the same rate with t-BuBr although they react at very different rates with Mel. Indeed, S l substitution reactions are generally best done with weaker, non-basic nucleophiles to avoid the competing elimination reactions discussed in Chapter 17. 

These values imply differences in the basicity, nucleophilicity and the reactivity of Co-O complexes, which is supported by some... 

R-Y-COCl plays the key role in phosgenation reactions that are of a stepwise nature the major part of these processes is COCl (chlorocarbonyl) transfer to R-Y-H generating chloroformates, carbamoyl chlorides, etc. R-Y-COCl is of limited (low) stability and this is the driving force behind its intermediacy in the synthesis of chlorides and isocyanates under elimination conditions (eliminating CO2 and/or HCl), and also determines the character of a reactive substrate in further nucleophilic substitutions to form symmetrical and unsymmetrical substituted carbonic acid derivatives carbonates, carbamates, ureas) or diaryl ketones. Commonly, chloro-formylation and isocyanate formation are independent of the nature of R. Obviously, the reactivity is very different due to the relative basic/nucleophilic ratio. For example, Ar-Cl cannot be prepared through a chloroformate intermediate nor by direct phosgenation, but the reaction does work well in the aliphatic series. 

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