Editing Kinetic isotope effect (section)

==== Organometallic reaction mechanism elucidation examples ====
Colletto et al. developed a regioselective β-arylation of benzo[b]thiophenes at room temperature with aryl iodides as coupling partners and sought to understand the mechanism of this reaction by performing natural abundance KIE measurements via single pulse NMR.<ref name=":1">{{cite journal | vauthors = Colletto C, Islam S, Juliá-Hernández F, Larrosa I | title = Room-Temperature Direct β-Arylation of Thiophenes and Benzo[b]thiophenes and Kinetic Evidence for a Heck-type Pathway | journal = Journal of the American Chemical Society | volume = 138 | issue = 5 | pages = 1677–83 | date = February 2016 | pmid = 26788885 | pmc = 4774971 | doi = 10.1021/jacs.5b12242 | bibcode = 2016JAChS.138.1677C }}</ref>
[[File:Reaction scheme for the beta arylation of benzo b thiophenes.png|none|thumb|553x553px|Regioselective β-arylation of benzo[b]thiophenes. HFiP (usually HFIP) refers to [[hexafluoroisopropanol]], or CF<small>3</small>-CHOH-CF<sub>3</sub>]]

[[File:1H KIEs for beta arylation of benzo b thiophenes.png|none|thumb|200x200px|{{sup|2}}H KIEs measured at natural abundance]]

[[File:13C KIEs for beta arylation of benzo b thiophenes.png|none|thumb|200x200px|{{sup|13}}C KIEs measured at natural abundance]]

The observation of a primary {{sup|13}}C isotope effect at C3, an inverse {{sup|2}}H isotope effect, a secondary {{sup|13}}C isotope effect at C2, and the lack of a {{sup|2}}H isotope effect at C2; led Colletto ''et al.'' to suggest a Heck-type reaction mechanism for the regioselective {{math|β}}-arylation of benzo[b]thiophenes at room temperature with aryl iodides as coupling partners.<ref name=":1" />

Frost ''et al.'' sought to understand the effects of [[Lewis acid]] additives on the mechanism of enantioselective [[palladium]]-catalyzed C-N bond activation using natural abundance KIE measurements via single pulse NMR.<ref name=":2">{{cite journal | vauthors = Frost GB, Serratore NA, Ogilvie JM, Douglas CJ | title = Mechanistic Model for Enantioselective Intramolecular Alkene Cyanoamidation via Palladium-Catalyzed C-CN Bond Activation | journal = The Journal of Organic Chemistry | volume = 82 | issue = 7 | pages = 3721–3726 | date = April 2017 | pmid = 28294618 | doi = 10.1021/acs.joc.7b00196 | pmc = 5535300 }}</ref>
[[File:Enantioselective intramolecular alkene cyanoamidation reaction scheme.png|none|thumb|513x513px|Enantioselective intramolecular alkene cyanoamidation]]
[[File:13C KIEs for enantioselective intramolecular alkene cyanoamidation reaction scheme.png|none|thumb|542x542px|{{sup|13}}C KIEs for enantioselective intramolecular alkene cyanoamidation reaction (left no additive, right add BPh{{sub|3}})]]
The primary {{sup|13}}C KIE observed in the absence of BPh{{sub|3}} suggests a reaction mechanism with rate limiting cis oxidation into the C–CN bond of the [[cyanoformamide]]. The addition of BPh{{sub|3}} causes a relative decrease in the observed {{sup|13}}C KIE which led Frost et al. to suggest a change in the rate limiting step from cis oxidation to coordination of palladium to the cyanoformamide.<ref name=":2" />