Functional groups, recognition

Although the feasibility of direct probe MS for the analysis of additives in complex polymeric matrices has been demonstrated (Section 6.4), application is limited, difficult and requires above-average mass-spectroscopic expertise. Direct desorption in the MS probe is usually limited to screening of volatile components. Direct multicomponent spectroscopic analysis has other hurdles to overcome (UV/VIS lack of spectral discrimination IR/R functional-group recognition only, with no discriminative power for additives with similar functionalities NIRS unsuitable for R D problems NMR sensitivity). 

Before the development and widespread application of spectroscopic methods for the elucidation of structure, confirmation of the class type of an unknown organic compound was completed by the preparation of two or more crystalline functional derivatives. If the compounds had been previously reported in the literature, agreement between the published physical constants of the derivatives with those prepared by the worker was accepted as proof of identity. In many cases, and particularly in natural product chemistry, functional group recognition led to oxidative, reductive, or hydrolytic breakdown into smaller carbon-containing fragments. These were, if necessary, separated, characterised and identified by derivative preparation. The reassembly of the jig-saw of fragments inferred by the identity of the fission products, then led to postulated structures. 

The dimer and the catemer motifs are patterns commonly observed for carboxylic acids [16] as well as for amides (Fig. la) [17]. A dimer is formed whenever hetero-functional group recognition between a carboxylic acid and an amide is available (Fig. lb). This finding has been well documented and used in connection with carboxylic acid receptors [18]. Desiraju has also identified synthons based on the same geometry but with different hydrogen bonding... 

Ito. T. Biihlmaim. P. Umezawa. Y. Polypyrrole-modified tips for functional group recognition in scanning tunneling microscopy. Anal. Chem. 1999. 71. 1699-1705. 

Hollingsworth. M.D. Cyr. N. Solid-state NMR studies of functional group recognition in channel inelusion com- 62. pound formation. Mol. Ciy st. Liq. Cryst. 1990. 187, 135. 

Chen, H., Cotte-Rodrfguez, I., Cooks, R.G. (2006) c -Diol Functional Group Recognition by Reactive Desorption Electrospray Ionization (DESI). Chem. Commun. 597-599. 

On completion of the functional group recognition the first class of objects, i.e., acyclic chains bearing heteroatoms and linked with chemical functionality, are fully selected from the input structure, hierarchically ordered or ranked, and preliminarily identified to an extent enabling their naming. Further phases of the naming cycle must identify the other two classes of objects, i.e., ring systems and chains,... 

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