Interaction of an organic molecule's reaction center with unconjugated electrons
In organic chemistry, neighbouring group participation (NGP, also known as anchimeric assistance) has been defined by the International Union of Pure and Applied Chemistry (IUPAC) as the interaction of a reaction centre with a lone pair of electrons in an atom or the electrons present in a sigma or pi bond contained within the parent molecule but not conjugated with the reaction centre.[1][1][2][3] When NGP is in operation it is normal for the reaction rate to be increased. It is also possible for the stereochemistry of the reaction to be abnormal (or unexpected) when compared with a normal reaction. While it is possible for neighbouring groups to influence many reactions in organic chemistry (e.g. the reaction of a diene such as 1,3-cyclohexadiene with maleic anhydride normally gives the endo isomer because of a secondary effect {overlap of the carbonyl group π orbitals with the transition state in the Diels-Alder reaction}) this page is limited to neighbouring group effects seen with carbocations and SN2 reactions.
^de Rooij, J. F.; Wille-Hazeleger, G.; Burgers, P. M.; van Boom, J. H. (1979). "Neighbouring group participation in the unblocking of phosphotriesters of nucleic acids". Nucleic Acids Research. 6 (6): 2237–2259. doi:10.1093/nar/6.6.2237. PMC 327848. PMID 461188.
^Stalford, Susanne A.; Kilner, Colin A.; Leach, Andrew G.; Turnbull, W. Bruce (2009-12-07). "Neighbouring group participation vs. addition to oxacarbenium ions: studies on the synthesis of mycobacterial oligosaccharides". Organic & Biomolecular Chemistry. 7 (23). Royal Society of Chemistry: 4842–4852. doi:10.1039/B914417J. PMID 19907773.
^Bowden, Keith (1993-01-01). "Neighbouring Group Participation by Carbonyl Groups in Ester Hydrolysis". In Bethell, D. (ed.). Advances in Physical Organic Chemistry Volume 28. Advances in Physical Organic Chemistry. Vol. 28. Academic Press, ScienceDirect. pp. 171–206. doi:10.1016/S0065-3160(08)60182-3. ISBN 9780120335282. Retrieved 2019-12-17.
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