Nitrenes definition

When mesitylene-2-sulphonyl azide (3) is heated to 150 °C in n-dodecane, a Curtius-type rearrangement of the nitrene (4) occurs as discussed in Section 2.1 i to give 2,4,6-trimethylaniline and the hexa-methylazobenzene 14>. A similar result has now been observed by a careful analysis of the thermolysis products of durene-3-sulphonyl azide in w-dodecane at 150 °C. The amine is definitely formed but the azo-compound could barely be detected 13>. 

In conclusion, after having been a firm point for about twenty years, the intermediate formation of nitrene species is now a matter of debate. As mentioned in the introduction to this paragraph, the debate has been based more on indirect evidences and general feelings rather than on any unquestionable evidence. Such an evidence is still required before a definitive answer can be given to this problem. 

The proposal that low isotope effects may be associated with bent transition states was made before Westheimer s treatment of linear transition states became available [93]. Nonetheless experimental confirmation would clearly provide evidence in its support. In fact there are a number of reactions, most notably 1,2-hyride rearrangements and carbene and nitrene insertions, for which the consistent observation of small isotope effects can reasonably be ascribed to non-linear transition states [90]. On the other hand the mechanisms of the reactions have not always been entirely clear and it may perhaps be questioned whether a definite and general conclusion can yet be drawn. 

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