Aliphatic compounds, electrophilic reactions

Self-Assessment Exercises 79a. Nucleophilic substitution corresponds to a substitution (either Sxjl or S[.j2) for aliphatic compounds. Electrophilic aromatic substitution is typical for aromatic compounds (an atom is replaced by an electrophile) 79b. An addition reaction is the opposite of an elimination reaction. In an addition reaction, two or more atoms (molecules) combine to form a larger one. 79c. S[,jl reaction involves the formation of carbocation. Sf.j2 reaction, on the other hand, is a one-step process in which bond breaking and bond making occur simultaneously at a carbon atom with a suitable leaving group. 79d. El reactions are unimolecular elimination reactions that proceed via carbocation intermediates. E2 reactions are bimolecular, one-step reactions that require an antiperiplanar conformation at the time of rr-bond formation and /3-bond breaking and do not involve carbocations. 

Volume 8 Volume 9 Volume 10 Volume 12 Volume 13 Proton Transfer Addition and Elimination Reactions of Aliphatic Compounds Ester Formation and Hydrolysis and Related Reactions Electrophilic Substitution at a Saturated Carbon Atom Reactions of Aromatic Compounds Section 5. POLYMERISATION REACTIONS (3 volumes)... 

ZnBr2 also is an effective catalyst for the carbonyl insertion (Equation (75)).290 The Zn-catalyzed reaction is applicable to various aldehydes and ketones including aliphatic compounds. In sharp contrast to the Cu-catalyzed reaction, the carbonyl insertion occurs on the less substituted side with high regioselectivity. ZnBr2 most likely serves as electrophilic activation of carbonyl compounds. 

There are various reasons that may lie behind this development. First, for almost 100 years, electrophilic substitutions were a domain of aromatic chemistry and, at least before Huisgen s review (1955) on the reactivity of diazoalkanes, the large majority of organic chemists did not spend much time on the question that, apparently, there are no similarities between aromatic and aliphatic diazo compounds. Second, it is obvious — even today — that electrophilic substitution reactions of aliphatic diazo compounds are more complex and, therefore, less predictable than the substitution of sp -hybridized C-atoms in aromatic and aliphatic compounds by arenediazonium ions. 

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