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Originally Posted by Kharakov
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Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C2 symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C2 jump rate is much faster than the tetrahedral jump rate. 2H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above.
For hydrated Zeolite A, the kinetic activation parameters (dH, dS) for the tetrahedral and C2 symmetry jumps are: dHtet = +17 kJ/mol, dStet = −109 J/(mol K), and dHc2= +19 kJ/mol, dSc2= −20 J/(mol K). For kanemite, dHtet = +23 kJ/mol, dStet = −69 J/(mol K), and dHc2= +23 kJ/mol, dSc2= −11 J/(mol K).
...C2 jumps???
Quote:
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Originally Posted by google:
"C2 jumps" NMR
A multinuclear nuclear magnetic resonance study of t-butylthiol
SANDRMAO OIBROEKAN' D RODERICKE. WASYL~SHEN
Depczrtnlerlt of Chernistry, Dc~lhortsie University, Hnlgczx, N.S., Ccznnda B3H 453
Received February 12, 1985
A multinuclear nuclear magnetic resonance study of t-butylthiol
or
http://article.pubs.nrc-cnrc.gc.ca/p...startPage=2926
In the rapid motion limit, the effect of jumps between sites of three-fold or greater symmetry is exactly the same as for rotational diffusion. Once this limit is reached, one cannot distinguish, for example, between 120" jumps or continuous rotation about a C3 axis. On the other hand, rapid jumps and diffusion about a C2 axis yield substantially different spectra (7-9, 11, 12). Theory predicts that 180" flips about a C2 axis in t-butyl compounds will result in an effective asymmetry parameter of 1....
The situation for more complex motion - e.g. a combination of C2 jumps and Cx jumps about different axes - is much more complex, and will not be dealt with here.
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Since neither rapid diffusion or fast C3 jumps predict [asymmetry], the highly asymmetric lineshapes observed in this phase imply that C2 jumps must be involved in the reorientation of the molecule.
Further discontinuous changes in the deuterium nmr line-shapes do not take place until 164 K (d.o. compound) or 166 K (SD isotopomer), corresponding to the solid 111 --> solid 11 phase transition. At 164 K, the ...spectrum... undergoes further narrowing to a featureless peak of - 1 kHz in width with low intensity shoulders. |
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Ack! What an interesting way to waste a couple of hours.
So the C2 orientation is the one between the tetrahedral (C3) orientation (through the center of the face rather than thru the corners of the cube).
The one which HBond notes predominates in some bonding situations.
Thanks HB, ...interesting as always....
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Kharakov, that was a fascinating link on the Zeolite/kanemite hydration studies.
Thanks mucho:
It's neat that they include the Entropy, dS (delta S), in their measurements of the kinetic activation energies for these different conformations of "orbitals." ...the tetrahedral is more stable by a few Joules (compare with the
kiloJoules for the OH bonds).
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Whatever the precise details are, IMHO it's obvious that the changing shape of water molecules in various conditions (including phase changes) affects its packing behaviour--and thus its volume.
...as to the hot water freezing faster "topic" I don't know, but the dissolved gases theory sounds plausible....
This would be a good Science Fair Project for some kids!
~
