Molecular migration

For books, see Mayo, P. de Rearrangements in Ground and Excited States, 3 vols. Academic Press NY, 1980 Stevens, T.S. Watts, W.E. Selected Molecular Rearrangements Van Nostrand-Reinhold Princeton, 1973. For a review of many of these rearrangements, see Collins, C.J. Eastham, J.F. in Patai The Chemistry of the Carbonyl Group, vol. 1 Wiley NY, 1966, p. 761. See also the series Mechanisms of Molecular Migrations. 

In an early study, Mauritz et al. investigated anion—cation interactions within Nation sulfonate membranes versus degree of hydration using FTIR/ ATR and solid state NMR (SSNMR) spectroscopies. An understanding of the dynamic ionic—hydrate molecular structures within and between the sulfonate clusters is essential for a fundamental understanding of the action of these membranes in ion transport. This information can be directly related to the equilibrium water swelling that, in turn, influences molecular migration. 

B. S. Thyagarajan, ed., Mechanisms of Molecular Migrations, Vols. 1—4, Wiley-Interscience, New York, 1968-... 

Figures 1,2, and 3 show stereoscopic views of their crystal packing. It is clearly seen that the exo-bicyclo [2.2.1] anhydride 1 has a hardly interlocked monolayer structure and so does the endo isomer 2 except for slight interpenetrations. These structural features facilitate molecular migrations upon chemical reaction, whereas the bicyclo[2.2.2] anhydride 3 exhibits strong interlocking, preventing molecular migrations.

The gas-solid neutralizations found more interest than the solid-solid variant. The quantitative reactions of gaseous ammonia with solid benzoic and related acids were interpreted by a concept of gas permeability of the crystal in order to explain anisotropic reaction fronts in single crystals [24]. Also, the ammonium salts of the aromatic or aliphatic mono- and dicarboxylic acids 16-21 (Scheme 3) formed the corresponding salts with 100% yield. The need for molecular migrations immediately upon reaction was not considered at that... 

Solid tertiary amines and imines may be quantitatively alkylated by gas-solid and solid-solid techniques. Methylation of quinuclidine (176) to give the methoiodide 177 is achieved waste-free by exposure of 176 to a stoichiometric amount of methyl iodide vapor (Scheme 23). Difficulties with the disintegration of the crystals of 177 from those of 176 (reaction step 3) are overcome by ultrasound treatment from a cleaning bath at 20 °C [22]. Numerous applications of this technique to tertiary amines can be envisaged. However, solid Troeger s base (with interlocked layers, i.e., no possibility for molecular migrations) is not alkylated by methyl iodide vapor unless an excess of the vapor is applied to induce intermediate (partial) liquefying of the solid [22]. 

The first solid-state linear dimerization was observed with N-vinylpyrrolidi-none. It was first quantitatively converted to its Markovnikov HBr addition product (by application of HBr gas at -40 °C), which upon warming to room temperature lost HBr and formed ( )-l,r-(3-methyl-l-propene-l,3-diyl)bis-(2-pyrrolidinone), but the yield was less than 100% [58]. Interestingly, such head-to-tail dimerizations of alkenes lead to shrinking and that may create reactivity even if the crystal lattice does not allow for molecular migrations due... 

A possible (so far unjustified) enhancement of the polymer concentration within pores due to molecular migration phenomena. The enhanced pore concentration may result in greater partitioning into the very small pores and in the increased retention volumes. 

J. J. Gajewski, mMechanisms of Molecular Migrations, B. Thyagarajan, Ed., John Wiley Sons, Inc., New York, 1971. 3, p. llff. 

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