density the results of the previous section would predict that only three T values would be found for any member of the series. Such is indeed the case (3). Again since the measured T depends on the electron density the eqns. (Q),( l o ) ,and (11) would indicate that the r value for a given type of proton would change with a change in n . Indeed T appears (3) to depend on 1 / n and the linear relation rr = (k, k t ) l / n has been adopted to fit the experimental results. The r values are then described by
+
Combination of the appropriate equations for p and T [e.g. (9) with (12)] yield the direct relation between chemical shift and electron density. For the protons attached to carbon atoms in the chain the relations are
while for the methyl protons the relation is n = +27
pi
+&
(16)
That approximately the same sensitivity of T to p (11.4 and 1 1 6 ) is obtained for both protons in eqn. (15) is t o be expected for the protons are bonded directly to the carbons by a single u bond. On the other band the methyl protons are located two u bonds away from the terminal carbon and hence their T values will be less sensitive (2 8 ) to the ~r-electrondensity. The values obtained here for the proportionality constants are quite close (11.5 versus 10 7 and 2.8 versus 3.27 or 4.25) to those obtained by more sophisticated procedures Exercises for the Undergraduate
All the calculations of the foregoing can be carried out readily by the undergraduate. The procedure for
the uv results is simple and in any case the methods, or very similar ones, are well documented elsewhere ( I , % . However for the nmr correlation many values of pi must be calculated and the student might well be presented with a table of electron densities, essentially Table 2 with a few blanks, and asked to fill in the missing values by carrying out the appropriate manipulations with the molecular orbital wave functions [eqn. ( 8 ) ] . The values of pr may then be plotted against 1/n, the limiting straight lines found and finally the sensitivity of r to p obtained. Although these calculations in themselves constitute a reasonably satisfactory introduction to nv and nmr data and their derivation from energy levels and wave functions, the exercise can be extended by considering the analogous and more familiar cyanine dyes. For example the ions n = 0 , 1 , 2 of the series
are not readily dissolved in standard solvents; however for the ion n = 0 in DMSO a weak spectrum was obtained which showed an nmr transition at r - 4.4. The Amax for the same system is 480 mp. By assuming this system can be treated in the same way as the polyenylic system, the experimental Amax for cyanine dye n = 0 can be used to find the penetration p, this value of p used in eqn. ( 8 ) to obtain the p for n = 1 or 2 and finally the eqn. (15) used to give T for n = 1 or 2. Literature Cited (1) GERKIN,R. E., J. CHEM.EDUC.,42, 490 (1965). (2) SHOEMAKER, and GARLAND,"Ex eriments in Physical Chemistry'' (2nd Ed.), ~ c ~ r a w - l fBook i l Co., New York, N. Y., 1962. (3) SOUENSEN, T. S., J . Am. Chem. Sac., 87, 5080 '(1964). (4) OSEEN,R. B., FLEWWELLING, R. B., A N D LAIDLAW, W. G., J . Am. Chem. Sic., 90, 4209 (1968).
The Use of Rare Earths in Color TV 111 1964 the demand for yttrium and europium oxides for manufacture of the red phosphor for color T V tubes hecame acute.. . . The rare earth industry expanded production to the limit and then successfnlly developed new processes and built new facilities to meet the feverish demand for the phosphor chemicals. What appeared to be conservative estimates of the market were based on a potential use of 12-15 g of phosphor per TV tube. Industry forecasts for color T V tube production were a t least 7 million tubes in 1967 with further growth projected to 10 million tubes in 1969. This market information translated into an immediate demand for approximately 140,000 pounds of yttrium oxide and 10,000 pounds of europium oxide, gradually growing to 200,000 pounds and 14,000 pounds, respectively, in 1969. . . .With strong urging from the color TV tube and phosphor manufacturers, the rare earth industry succeeded in expanding production capacity t o well over 400,000 pounds of yttrium oxide and 24,000 pounds of europium oxide. Unfortunately, in February 1967, the bottom dropped out of the market. All deliveriesof yttrium and europium were cancelled or postponed.. . .However, after about six months of waiting, the rare earth industry was chagrined when it learned that the TV tube makers had meanwhile developed more efficient methods of applying phosphor to color TV tithes As a result of the improvement in efficiencythe amount of phosphor was reduced from 15 g to 5 g or less per tube. The amounts of yttrium and europium were reduced proportionately.. , . The complexity of the market, was increased when RCA announced its development of a new brighter red europium-activated yttrium oxysulfide phosphor. Also, today there is some indication that yttrium may be replaced to
of attention from scientists and engineers.
. . .Taken from "Research and the Hare Earth Business" by Joseph C. Schumaker, American Potash&Chemical Corporation, given at the 157th Meeting of the American Chemical Society, Minneapolis, 1969. Volume 46, Number 6, June 1969
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