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In their article, Wigman, Hart, and Gombatz report that disposable polyethylene cards can replace
Nujol mulls and KBr pellets (1). We have found that a single NaCl plate can be used in place of the polyethylene card. The resulting spectra are the same but cost is minimized since NaCl plates can be used again and again. The disadvantage is that since the NaCl plate should be
cleaned off immediately with fresh CH2Cl2, more methylene chloride is used and there is nothing permanent to keep, as there is with KBr pellets and the disposable cards..
Experimental Procedure: The spectra below
are of trans-1,2-dibenzoylethylene, from Acros, Cat. #
11,285-250. Spectrum A is on a disposable polyethylene IR
card, Type 61, from 3M.
Spectrum B is on a single
undrilled NaCl plate from Perkin-Elmer, part 027 1182.
Spectra were recorded on a PE model 13210 IR
spectrophotometer. The methylene chloride solution was prepared
as in ref 1; this solution was evaporated in the hood from
a disposable card and NaCl plate at the same time.
The shift in transmittance at 2000
cm{1 where gratings change is more pronounced for the NaCl plate
and the baseline is less linear with the card, but in each
case the absorptions are clearly occurring at the same
wavelength. In our organic chemistry course, we use IR mainly to verify that the correct product has been produced. This single NaCl plate method is certainly adequate for this use and other qualitative determinations.
Literature Cited
- Wigman, L. S.; Hart, E. E.; Gombatz, C. J. Chem. Educ. 1996, 73, 677.
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