1.4- Diaminobutane, basicity

While all strain effects in monoamines are basicity weakening, it is possible to find cases in di- and polyamines where strain is relieved upon protonation, leading to increased basicity. This phenomenon is observed in 1,4-diaminobutane derivatives where an almost linear N... H—(N+) hydrogen bond in the mono-protonated derivatives leads to a stable, seven-membered ring structure. Thus, for example, the measured PA of l,6-diazabicyclo[4.4.4]tetradecane (73) is 228.3 kcalmol-1, about 11 kcalmol-1 higher than its monoamine analog 75, despite the similar, inwardly pyramidalized, nitrogen conformation of both neutral amines. 

Only a small number of structures containing seven-membered chelate rings are known (50, 51) Tris(1,4-diaminobutane)cobalt-(III) ion is a third member of a basic series of structures ... 

For the intramolecular catalysis in the aminolysis of N-acetyl-imidazole by diamines [68, 69] the catalytic group is in the same molecule as the nucleophile, and the problem of distinguishing between nucleophilic and general base catalysis does not arise. The rate law for the aminolysis of N-acetylimidazole by monoamines has both terms of first and of second order in amine, but in the aminolysis by ethylene diamine the term which is first order in amine is relatively more important. The rate constant for this reaction is 186 times greater than that for a monoamine of comparable basicity and a similar rate enhancement is found for the reaction with 1,3-diaminopropane. Rather smaller rate enhancements are found with 1,4-diaminobutane and 1,5-diaminopentane (see Table 4). Intramolecular catalysis is also found in the aminolysis of methyl formate... 

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