Alkyl group substitution, hydrogen bonds

Another factor affecting the nucleophilicity of these ions is their solvation, particularly in protic solvents. A protic solvent is one that has acidic protons, usually in the form of O—H or N—H groups. These groups form hydrogen bonds to negatively charged nucleophiles. Protic solvents, especially alcohols, are convenient solvents for nucleophilic substitutions because the reagents (alkyl halides, nucleophiles, etc.) tend to be quite soluble. 

We have seen many reactions where nucleophiles attack unhindered alkyl halides and tosylates by the SN2 mechanism. An enolate ion can serve as the nucleophile, becoming alkylated in the process. Because the enolate has two nucleophilic sites (the oxygen and the a carbon), it can react at either of these sites. The reaction usually takes place primarily at the a carbon, forming a new C—C bond. In effect, this is a type of a substitution, with an alkyl group substituting for an a hydrogen. 

The hydrogen-bonding energy seemed to contribute to the retention on the graphitized carbon (Hypercarb ) column, but not to the retention on another carbon BioTechnologyResearch (BTR ) column. Therefore, only alkyl-group-substituted compounds were selected and their log k values were correlated with MI values. The correlation coefficient was 0.718 for log A ref- The log A ref values of benzene, toluene, o- grlene, m- ylene,p- g lene, o-te/t-butylphenol, 4-ethylphenol,... 

The alkylation desctibed in this article is the substitution of a hydrogen atom bonded to the carbon atom of a paraffin or aromatic ring by an alkyl group. The alkylations of nitrogen, oxygen, and sulfur are described in separate articles (see Amines Ethers). 

Olefin Complexes. Silver ion forms complexes with olefins and many aromatic compounds. As a general rule, the stabihty of olefin complexes decreases as alkyl groups are substituted for the hydrogen bonded to the ethylene carbon atoms (19). 

Replacement of some or all of the —CONH— hydrogens by alkyl or alkoxy-alkyl groups to reduce hydrogen bonding which results in softer, lower melting point and even rubber polymers (A-substitution). 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

Treatment of an alkyl halide with a strong base such as KOH yields an. alkene. To find the products in a specific case, locate the hydrogen atoms on each carbon next to the leaving group. Then generate the potential alkene products by removing HX in as many ways as possible. The major product will be the one that has the most highly substituted double bond—in tints case, 1-methylcyclohexene. 

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