Intra-molecular rearrangement

The reaction occurs with technical material only, and, once formulated, the nitrosamine content is not altered as a function of time at ambient formulation temperatures. This intra-molecular rearrangement requires careful attenticn to conditions in the formulation of dinitroaniline herbicides. 

Flash vacuum thermolysis of 6-chloro-3-diazoindazole (2b) resulted, upon loss of nitrogen, in the formation of carbene 102, which could intra-molecularly rearrange to the nitrene 103, or to the azabenzocyclopropene 104, or to azacycloheptatrienylidene 105 (Scheme 29). The only isolable product was 106, formed by dimerization of the nitrene 103 (78CB2258). 

Perfluoralkyl-alkenes like 1-perfluorooctyl-5-methylhex-2-en (usually abbreviated as RMN3, [24]) can be regarded in the same way. In addition to the saturated analogues, it has to be ensured by the molecular structure that no inter- or intra-molecular rearrangements take place, generating acid by-products. 

Isocyanides, when heated in the gas phase or in nonpolar solvents, undergo a 1,2-intra-molecular rearrangement to nitriles RNC — RCN.31 1 In polar solvents the mechanism is different.3111... 

Acetanilide and its homologues undergo intra-molecular rearrangement when reduced, and the corresponding amines are formed —1... 

Scheme 2.1.9 An examples of twofold intra-molecular rearrangement monitored by Sn, 6 and N NMR ...

N-Acetylation of isatin with acetic anhydride yields N-aeetylation whieh undergoes intra molecular rearrangement with alkali to the quinoline eompound 2-hydroxyeinehoninie acid under the name Pfitzinger Reaction. The diamino group is now introdueed under eontrolled condition at room temperature so as to avoid reaction with relatively less reactive 2-ehloro substituent. 

Armor and Taube also found (33) that if N-labelled N2O is used, the resulting N2 complex slowly isomerizes to give a random distribution of in the linearly coordinated N2 molecule. Since the rate of isomerization is rather faster than the rate of dissociation of N2 from the complex, they postulate an intra-molecular rearrangement involving a sideways-on TT-bonded transition state... 

Scheme 3(a). Absence of an intra-molecular rearrangement in protonated iso-butane. 

A splendid illustration of the use of 500 MHz NMR is provided by the water suppressed time course of porphyrin biosynthesis where porphobilinogen (PEG), the substrate for uro gens I and m and Vitamin 3 2 is transformed into the apparent product uro gen I which turns out to be a chemical artifact. Thus, during incubation of PEG with the enzyme, PEG deaminase ([D] Fig. 1 Mj. 33,000) the product released from the enzyme is pre-uro gen, or hydroxymethyl bilane (HME), whose characteristic spectrum (Fig. 1) (t 2 = 180 sec/30 C) can be seen transiently when the reaction is carried out at 4 C [12a,b]. The NMR method also uniquely defines HME as the substrate for the second enzyme, uro gen ni cosynthetase. In the absence of the latter enzyme, the cyclization of the head-to-tail tetrapyrrole HME takes place spontaneously. The deep-seated intra-molecular rearrangement of HME to uro gen El can now be studied by this technique. 

The format of this chapter has been altered slightly from that of previous years in response to changes in the research activity in various areas of work, e.g. a section on (T-bonded hydrocarbon ligands has now been included. The decision to continue to include some papers concerned with inter- and intra-molecular rearrangements is somewhat arbitrary since they could equally well have been discussed in Chapter 6. However, it seems more appropriate to bias the coverage in that chapter towards studies involving fluxional molecules although some overlap may be noticed occasionally. 

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