Bee alarm pheromone

Brodmann, J., Twele, R Francke, W Yi-bo, L Xi-qiang, S. and Ayasse, M. (2009). Report orchid mimics honey bee alarm pheromone in order to attract hornets for pollination. Current Biol., 19, 1368-1372. 

The problem with E.I. is that for many radical cations even 20 p,s is too long, and all the molecular ions have decomposed by the time they reach the detector. The fragments produced maybe useful in identifying the molecule, but even in the case of the bee alarm pheromone it would obviously be bet-ter to get a stronger and more convincing molecular ion as the weak (5%) peak at 114 might also be a fragment or even an impurity. 

For the bee alarm pheromone, the accurate mass turns out to be 114.1039. Table 3.4 compares possible atomic compositions, and the result is conclusive. The exact masses to three places of decimals fit the observed exact mass only for the composition C7H140. You may not think the fit is very good when you look at the two numbers, but notice the difference in the error expressed as parts per million. One answer stands out from the rest. Note that even two places of decimals would be enough to distinguish these four compositions. 

Table 3.4 Exact mass determination for the bee alarm pheromone ...

This is what happens when a proton couples to different groups of protons with different coupling constants. Many different coupling patterns are possible, many can be interpreted, but others cannot. However, machines with high field magnets make the interpretation easier. As a demonstration, let us turn back to the bee alarm pheromone that we met in Chapter 3. An old 90 MHz NMR spectrum of this compound looks like this. 

Ordinary mass spectra tell us the molecular weight (MW) of the molecule we could say that the bee alarm pheromone was MW 114. When we said it was C7H14O we could not really speak with confidence because 114 could also be many other things such as CgH g or CgHio02 or CgHi4N2. These different atomic compositions for the same molecular weight can nonetheless be distinguished... 

For the bee alarm pheromone, the accurate mass turns out to be 114.1039. Table... 

GH3)jGHGH2GH200GGH3, which is a bee alarm pheromone that signals danger to a honey bee. If this compound is warmed with aqueous sodium hydroxide, a slow reaction takes place to produce sodium ethanoate and 3-methylbutan-l-ol. The reaction is first order with respect to both 3-methylbutyl ethanoate and the aqueous hydroxide ion. Explain the term first order and give experimental details showing how this information could be obtained. [8]... 

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