Solvolysis of (Z)-5-Trimethylstannyl 2-Adamantyl p-Bromobenzenesulfonate: Mechanistic Implications of a Record-Breaking Secondary α-Deuterium Kinetic Isotope Effect for an S_N1 Substrate

Abstract

The secondary alpha-deuterium kinetic isotope effect (alpha-kie) for the solvolysis of (Z)-5-trimethylstannyl 2-adamantyl p-bromobenzenesulfonate in 97% w/w aqueous 2,2,2-trifluoroethanol (97T) at 25 degrees C has been measured (k(H)/k(D) = 1.33). The alpha-kie is abnormally high compared to the value of 1.23 for the corresponding limiting S(N)1 solvolysis of 2-adamantyl p-bromobenzenesulfonate, which proceeds via an extended ion-pair mechanism. A novel mechanism for the solvolysis of the tin compound is proposed that accommodates not only the high alpha-kie but also the absence of internal return.

Activation of C–O and C–F Bonds by Pincer–Iridium Complexes

“…This value may be decomposed as the product of (i) the equilibrium isotope effect (EIE) for the pre-equilibrium of free ether plus (PCP)Ir precursor (e.g., (PCP)Ir(TBV)H) with the aryloxymethyl hydride/deuteride, calculated to be 3.13; and (ii) the secondary KIE for α-aryloxide migration, calculated as 1.33. The EIE of 3.13 is slightly higher than typical C-H(D) addition EIEs [53,54]; this may be attributable to low Ir-H(D) bending frequencies in the addition product resulting from the shallow energy surface for deformation of the ligand arrangement in the equatorial plane of the five-coordinate d 6 bond) may seem high for a secondary KIE, but it is fully consistent with the KIE reported for related S N 1 reactions of organic species with oxygenate-leaving groups, for which values above 1.2 per H/D atom are common [56][57][58][59][60][61][62][63].…”

Efficacy of irrigation systems on penetration of sodium hypochlorite to working length and to simulated uninstrumented areas in oval shaped root canals

“…This irrigation system has been demonstrated to remove pulp debris (Nielsen & Craig Baumgartner 2007, Parente et al 2010, Adcock et al 2011) and achieve effective disinfection (Hockett et al 2008 in the apical third. On the contrary, the results obtained with positive pressure irrigation failed to demonstrate irrigation of the apical third, confirming the need for adding an alternative activation system (Adcock et al 2003, Carver et al 2007). Although some have reported better disinfection of the root canal using the SAF system (Siqueira et al 2010), the overall microbial reduction could have been related to the coronal and mid-root areas.…”

“…2010) in the apical third. On the contrary, the results obtained with positive pressure irrigation failed to demonstrate irrigation of the apical third, confirming the need for adding an alternative activation system (Adcock et al. 2003, Carver et al.…”

12 Reaction mechanisms : Part (ii) Polar reactions

“…The secondary a-deuterium kinetic isotope effect for the solvolysis of (Z)-5trimethylstannyl 2-adamantyl p-bromobenzenesulfonate 27 in 97% w/w aqueous 2,2,2 trifluoroethanol at 25 uC has been measured (k H /k D ~1.33). 14 The a-KIE is abnormally high compared to the value of 1.23 for the corresponding limiting S N 1 solvolysis of 2-adamantyl p-bromobenzenesulfonate 26, which proceeds via an extended ion-pair mechanism. A novel mechanism for the solvolysis of the tin compound is proposed that accommodates not only the high a-KIE but also the absence of internal return.…”