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Monday, December 21, 2015

NMR of the Christmas Tree

One of my fondest memories as a child is the colorful lights and especially the smell of a decorated Christmas tree.  The hot incandescent lights used years ago would heat up the tree evaporating the fragrant compounds in the needles producing the very memorable and wonderful smell of Christmas.  Although modern artificial Christmas trees and cool LED lights have made the holiday season safer with respect to fires, they have taken much of the magic out of Christmas.  Among many other compounds, it is pinene, bornyl acetate and citronellol that contribute to the Christmas smell of evergreen needles.
We can use NMR spectroscopy to look for these compounds and perhaps recover a bit of the Christmas magic.  The bottom panel of the figure below shows the 13C CPMAS spectrum of spruce needles.  One can easily identify the signals from cellulose in the CPMAS spectrum of the needles while some of the smaller peaks can be attributed to fragrant compounds.  Many of the fragrant compounds in the needles are likely to be in a liquid-like state and not cross polarize very well.  These will either be absent or under-represented in the CPMAS spectrum.  The top panel of the figure shows the 1H - 13C HSQC spectrum of a benzene-d6 extract prepared from crushed spruce needles.  The top and left-side projections are the high resolution 1H and 13C NMR spectra, respectively.  This sample is expected to contain all of the benzene soluble compounds.  The spectrum is free of cellulose resonances and shows a mixture of fragrant compounds.
These data don't recover the childhood magic of Christmas but they do bring a little bit of joy to this NMR spectroscopist.

Merry Christmas