Most acidic hydrogen

Amines or ammonia replace activated halogens on the ting, but competing pyridyne [7129-66-0] (46) formation is observed for attack at 3- and 4-halo substituents, eg, in 3-bromopyridine [626-55-1] (39). The most acidic hydrogen in 3-halopyridines (except 3-fluoropyridine) has been shown to be the one in the 4-position. Hence, the 3,4-pyridyne is usually postulated to be an intermediate instead of a 2,3-pyridyne. Product distribution (40% (33) and 20% (34)) tends to support the 3,4-pyridyne also. 

First, attempt to identify the most acidic hydrogen in the starting material, based on hybridization or on the nature of neighboring atoms. Explain your rationale. Next, examine the electrostatic potential map for starting material alkyne). Which hydrogen appears to be most electron poor Is this the one that you predicted What makes this hydrogen more electron poor than the others ... 

Identify the most acidic hydrogens in each of the following compounds, and tank the compounds in order of increasing acidity ... 

For a given a hydrogen atom to be acidic, the C-H bond must be parallel to the p orbitals of the C=0 bond (that is, perpendicular to the plane of the adjacent carbonyl group). Identify the most acidic hydrogen atom in the conformation shown for the following structure. Is it axial or equatorial ... 

The principal product from l//,2//,4//-heptafluorocyclopentanes 17A and 17B is in each case the cyclopentene 18A and 18B, respectively, arising from elimination of the most acidic hydrogen. However, the minor product 48 arises from a syn elimination from cyclopentane 17A while it is produced in a larger proportion from 17B via anti elimination, giving some evidence that the latter process is slightly more favorable even in these cyclopcntane systems. 

The organo-lithium reagent can be made by exchange of Li for a halide or by deprotonation. With di-iodide 24, one iodine may be exchanged with one equivalent of BuLi and the aldehyde 25 is the product.6 The aromatic heterocycle isothiazole 26 has its most acidic hydrogen (marked) next to sulfur and it gives one aldehyde 27 in good yield.7... 

Which is the most acidic hydrogen in this compound ... 

Which is the most acidic hydrogen in each of these compounds a) H2NCH2CH2OH b) CH3CH2OH c) CH3SH... 

The most acidic hydrogen of 2,4-pentanedione is on the carbon between the two C=0 groups. If this hydrogen is removed, the new unshared electron pair of the conjugate base is delocalized onto both of the oxygens. The additional resonance stabilization causes this compound to be an even stronger acid. Its pKa is 9 it is a stronger acid than water. 

Explain which are the most acidic hydrogens in these compounds ... 

The key to working problems of this type is the same as it has been in previous chapters. First identify the nucleophile and the electrophile. In these particular reactions the nucleophile is generated by removal of the most acidic hydrogen (one on the carbon a to the carbonyl or cyano group) to generate an enolate or related anion. This is the nucleophile in an SN2 reaction. 

Again the best approach is to identity the site where the nucleophilic enolate anion forms, the a-carbon with the most acidic hydrogen. This carbon becomes bonded to the carbonyl carbon of the ester electrophile in the final product. 

Identify the electrophile and the nucleophile. The base (NaOEt) removes the most acidic hydrogen, the one on the carbon between the carbonyl groups of ethyl acetoac-etate, to generate the enolate anion. This nucleophile then attacks ai the /3-carbon of the Michael acceptor ... 

The base removes the most acidic hydrogen, and the resulting enolate anion undergoes a conjugate addition with the Michael acceptor ... 

Replacement of hydrogen in an aromatic ring by lithium is an electrophilic substitution, entry of lithium taking place in the second and fast step of the reaction the reaction mechanism parallels that for base-catalyzed hydrogen exchange. Since the most acidic hydrogen is replaced,... 

Acidic hydrogens are bold. The most acidic hydrogens are the two between the carbonyl groups in (b) and the hydroxyl hydrogen in (c). The hydrogens in (c) that are bonded to the methyl group are acidic (draw resonance forms to prove it). 

Similar behavior of the computation methods is found for nonidentity Sn2 reactions. The optimized geometries of the entrance and exit ion-dipole complexes (IDl and ID2) and TSs for Reaction 6.3-6.5 are shown in Figure 6.4. The entrance ion-dipole complex for Reaction 6.4 is nnnsual among the reactions discussed here. The ion-dipole complexes are characterized by the electrostatic interaction of the nncleophile with the most acidic hydrogen(s). In all of the other examples, the nncleophile associates with the methyl protons, bnt in 4-IDl, the most acidic proton is the alcohol hydrogen, so fluoride forms a hydrogen bond to it. For all three reactions, the TS displays the normal 8 2 features, namely, backside attack of the nucleophile accompanied by Walden inversion. They differ in how symmetric the... 

Identify the most acidic hydrogens in each of the following molecules... 

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