Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

A 1960s PhD. If In Doubt, Measure Something.

At this point I had difficulties, but since I had made some new amines in order to measure their acid-base equilibrium constants, I did just that. Then, I measured some rate constants for the reaction of the amines with dinitrochlorobenzene. I then had two Hammett lines, but none with mesomeric withdrawing substituents because the para cyano substituent had also refused to make the amine. Part of the reason was because the very aggressive conditions needed to stop urea formation also tended to hydrolyse the cyano group. I was now back to the Hammett rho factor. We knew the rho value for anilines and benzylamines, so we could estimate that for 2-phenylethylamines. The cyclopropyl group enhanced the rho value by about 30% over the ethyl group, which was consistent with my concept of conductance and two routes. This indicated (to me, anyway) an absence of conjugation, but it was hardly a definitive result. Meanwhile, those wretched styrenes had still not put in an appearance, but of course without the mesomeric withdrawing groups it probably did not matter. I had a rho value, and it appeared that it would be impossible to get such amines consistent with having mesomeric withdrawing substituents. (I have no doubt that a more skilled synthetic chemist may have had more success here, but not with the para nitro derivative. I found it interesting that somebody tried to make this a decade later, and reported the same trouble.)
 
What now? Suddenly, supervisor put in a cameo appearance. (The 9 month sabbatical had extended to over 16 months, by my calculations.) He had an idea: take the acids, which I had already made and measure the rates of reaction with diphenyldiazomethane. Nobody measured rates of reaction of acids with this material, so get data, pad out the thesis! I was a bit skeptical about this comment, but then again, getting a PhD did have a certain attraction, so off I went. Since apparently nobody had bothered to carry out this with any other acids, I also had to measure the reaction rates with benzoic acids, so I could make some estimate of what the rho values should be, and of course to get an idea of how much mesomeric effect could be expected from substituents. The benzoic acids were available, so this meant plenty of measurements. If nothing else, thesis padding would ensue!
 
The reaction of the acids with diphenyldiazomethane depends on the acidity, so I expected this to merely reproduce existing   data on the phenylcyclopropanecarboxylic acids, but suddenly I realized that supervisor had made a key advance. The reactions were carried out in toluene, and this amplified the differences in acidity. The net result was that all the rho values were much bigger than anybody else had managed to get, and this meant that experimental errors did not have such significance with respect to sigma values. The rho value for the cyclopropane ring was again roughly where I expected it, but now I had some mesomeric donors, the para methoxy and the para fluoro substituent, and furthermore, the para nitro and para cyano substituted acids were available to anchor the line at a greater distance from the rest of the substituents.
 
Joy to the world! These results were quite unambiguous: the para substitution offered no mesomeric donating properties. I had a conclusion! Thank you, supervisor! Unfortunately, this brought a major problem: the scientific community was coming to the conclusion that cyclopropane conjugated with adjacent unsaturation, and here was me with results saying it did not. The reason for the conclusion that it did were:
(a) Hammett rho values for 2-phenylcyclopropyl-X were about 30% higher than those for 2-phenylethyl-X
(b) Cyclopropyl stabilized adjacent positive charge
(c) Cyclopropyl adjacent to a chromophore such as a benzene ring gave a bathochromic shift to UV signals.
(d) MO theory, and in particular CNDO/2 computations, said it conjugated.
(e) Dipole moments of molecules such as cyclopropyl chloride were about 0.3 Debye less than, say, isopropyl chloride.
All was not bad, because there were also data that indicated that cyclopropane did not conjugate. There were also some almost confusing options, thus the fact that the C-Cl bond in cyclopropyl chloride was slightly shorter than alkyl chlorides could be explained in terms of changed hybridization, but what did that mean in relation to conjugation? So, I had a further problem: I had to write up. No problem with much of the thesis, until the conclusions, where I had to deal with (a) to (e). My choices were simple: I had to show that my results were wrong (most undesirable because that was guaranteed failure, and anyway, I backed them) or irrelevant (again, undesirable, as why had I chosen this project?) or I had to find an alternative explanation for (a) to (e). Welcome to the start of an unusual career! I was happy that I had (a) under control, but . . . To add to my problems, supervisor disappeared again, apparently seeking a better paying job in North America.
 
How many of other PhD students had to take on an essentially emerging scientific consensus amongst those who had influence, essentially on their own? The problem was, how to do it?
Posted by Ian Miller on Nov 23, 2012 6:01 AM Europe/London

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