Product analysis, reaction intermediates and isotopic labelling

1 Product analysis, reaction intermediates and isotopic labelling 

a reaction has to be characterised, i.e. identities and yields of products must be determined, and these aspects are covered generally in Chapter 2. Once these are known, alternative possible paper mechanisms can be devised. Each may take the form of a sequence of linear chemical equations, or a composite reaction scheme replete, perhaps, with curly arrows . The next stage is to devise strategies for distinguishing between the alternatives with a view to identifying the correct one or, more realistically, eliminating the incorrect ones wherever possible, one seeks positive rather than negative evidence. 

Positive identification or other unequivocal evidence for the involvement of the intermediate confirms the stepwise route (see Chapter 9) however, failure to detect the intermediate (i.e. negative evidence) is seldom solid proof of its non-involvement - the intermediate may be just too short lived to be detected by the methodology employed. On the other hand, positive evidence of a concerted route can be problematical and some ingenious experimental strategies have been developed to address this issue, see Chapters 9 and 11 [5], 

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