Basicity relation with reactivity

Tanaka [198] made an attempt to determine the contribution of ring strain and basicity to the reactivity of cyclic ethers in copolymerization by means of Gibbs polymerization energy. He derived a relation between the relative reactivities of an m-membered ring with i substituents to that of an n-membered cyclic ether with j substituents. He included a linear combination of their basicity differences, A(pKb)m and of Gibbs energy, A(AG)m., in his relation (a, b, and c are constants)... 

A systematic evaluation of the electron donor strengths of different amino groups by using NMR related with UV-Vis, IR and Raman, microwave and photoelectron spectral data, dipole moments, basicity, reactivity, electron and X-ray diffraction data and the results of quantum chemical calculations has been reviewed by Gawinecki and coworkers25. 

Chemistry in three dimensions is known as stereochemistry At its most fundamental level stereochemistry deals with molecular structure at another level it is concerned with chemical reactivity Table 7 2 summarizes some basic definitions relating to molec ular structure and stereochemistry... 

The rate of reaction of a series of nucleophiles with a single substrate is related to the basicity when the nucleophilic atom is the same and the nucleophiles are closely related in chemical type. Thus, although the rates parallel the basicities of anilines (Tables VII and VIII) as a class and of pyridine bases (Tables VII and VIII) as a class, the less basic anilines are much more reactive. This difference in reactivity is based on a lower energy of activation as is the reactivity sequence piperidine > ammonia > aniline. Further relationships among the nucleophiles found in this work are morpholine vs. piperidine (Table III) methoxide vs. 4-nitrophenoxide (Table II) and alkoxides vs. piperidine (Tables II, III, and VIII). Hydrogen bonding in the transition state and acid catalysis increase the rates of reaction of anilines. Reaction rates of the pyridine bases are decreased by steric hindrance between their alpha hydrogens and the substituents or... 

Halopyridines undergo self-quaternization on standing while the less reactive 2-halo isomers do not. However, more is involved here than the relative reactivity at the ring-positions. The reaction rate will depend on the relative riucleophilicity of the attack-ing pyridine-nitrogens (4-chloropyridine is more basic) and on the much lower steric hindrance at the 4-position. Related to this self-quatemization are the reactions of pyridine and picolines as nucleophiles with 4-chloro- and 2-chloro-3-nitropyridines. The 4-isomer (289) is. again the more reactive by 10-30-fold (Table VII, p. 276). 

Each volume will be thematic, dealing with a specific and related subject that will cover fundamental, basic aspects including synthesis, isolation, purification, physical and chemical properties, stability and reactivity, reactions involving mechanisms, intra- and intermolecular transformations, intra- and intermolecular rearrangements, applications as medicinal agents, biological and biomedical studies, pharmacological aspects, applications in material science, and industrial and structural applications. 

The most important heuristics relate to reaction conditions, in particular, to acid-base catalysis. Depending on whether acidic or basic conditions are specified, the reactivity of certain bonds is changed. As an example, under basic conditions the breakability of H-X bonds is increased in comparison with other bonds. In fact, the relative acidities of all H-X bonds (X = any other element) can be rapidly calculated in EROS, and this allows further distinction within this class of bonds. 

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