Pauline A. Clarke and Norbert F. Hepflnger Rensselaer Polvtechnic Institute Troy, New York, 12181
II
b Model
The use of three dimensional models to illustrate ternary chemical data, e. g., phase diagrams,' is widely known. However, the preparation of easily constructed models for the presentation of the relatively large hydroxyl proton shifts observed in the course of nuclear magnetic resonance studies for ternary (CCL) solutions of hydrogen bonding donor-acceptor pairs has received little attention. The appearance of deviations from a smooth curve for plots of acceptor mole fraction versus chemical shift separation of the donor resonances (Fig. I),in studies of binary and ternary hydrogen bonding systems using nmr techniques,? gave an indication of the presence of complex formation. Although curvature deviations can he noted on binary donor-acceptor dilution graphs, it is difficult to relate the maxima apparent in these curves to plots of CCL dilution of each binary data point (Fig: 2). A three dimensional model (Fig. 3) allows a comparison of both binary and ternaw dilution data, revealing the relationship Getween the maxima apparent on eac6 two dimensional graph. Seen in the xy plane of Figure 3 are the binary and ternary curves for dilution of the donor with acceptor (mole fraction of acceptor versus
br Ternary
Mution Studies
chemical shift separation of the -CHB and -OH peaks of methanol (the donor)). I n the yz plane of Figure 3 are shown the CC4 dilution curves of each binary donoraccept,or data point, ml CCL versus chemical shift separation of the alcohol peaks. Observation of the three dimensional model reveals the presence of several maxima not obvious from either Figure 1or 2.
PERETTI, E. A., J. CHEM. EDUC., 43 (5), 253 (1966). WEPFINGE~, N. F.,AND CLARKE, P. A., J . 078. Chem., 34, 2572 (1969).
Figure 1. A plot of mole fraction of acceptor versus chemical rhift reparation of the donor resonances for binary and ternary dilutions of donorocseptor pain.
lot
Fieuro 2. CCln.
A hvo dimensional
Figure 3.
A three dimensional model for ternary difution studies.
of donor-acceptor pair dilution with
Volume 48, Number 3, March 1971 / 193
The model developed for the present system is made of clear plastic sheets. The side walls and base are ' / p in. while each donor-acceptor dilution curve (xy plane) was drawn to scale on a '/]a-in. plastic sheet. The curves in the yz plane were "drawn" using black thread. Completion of this 9 X 8 X 13-in. model involved positioning each sheet to correspond to scale
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Journal o f Chemical Education
using small '/,in. plastic blocks. Although this model illustrates a hydrogen bonding dilution system, application of this idea to other ternary dilution studies is possible. The use of plastic sheets instead of wires allows a rigid surface which can safely be handled by students.
