Multinuclear NMR Study of the Solution Structure and Reactivity of Tris(trimethylsilyl)methyllithium and its Iodine Ate Complex

Abstract

The extreme steric bulk of tris(trimethylsilyl)methyl derivatives (1-X) provides interesting structural and dynamic behavior for study. Dynamic NMR studies on 1-SePh and 1-I showed restricted rotation around the C-Si bonds of each trimethylsilyl groups. An extensive multinuclear NMR study of natural abundance and (6)Li and (13)C enriched 1-Li revealed three species in THF-containing solvents, a dimer 1T, and two monomers, the contact ion pair 1C, and solvent separated ion pair 1S. Observed barriers for interconversion of 1-Li aggregates were unusually high (DeltaG(double dagger) ca. 9 kcal/mol for exchange of 1S and 1C, DeltaG(double dagger)(41) = 16.4 kcal/mol for exchange of 1T with 1C and 1S), allowing for study of reactivity of each aggregate individually. We can show that 1S is at least 50 times as reactive as 1C and at least 5 x 10(10) times as reactive as 1T toward MeI. The large difference in reactivity allowed further study on the mechanism of the lithium-iodine exchange of 1-I with 1-Li and characterization of the intermediate iodine ate complex 4. Additional calibrations are presented for the sensitive yet chemically inert (13)C NMR chemical shift thermometer 1-H.

Unambiguous evaluation of the relative photolysis rates of nitro indolinyl protecting groups critical for brain network studies

“…Fig. 5 shows 1 H NMR photolysis of MNI-Glu, 2.04 mM, over time (from bottom to top) [15][16][17]. The initial protons (6, 5, 2, Me, i and j) disappear over time while new species (6 0 , 5 0 , 2 0 , Me 0 , i 0 , and j 0 ) appear.…”

Recent Advances in Stereodynamics and Conformational Analysis by Dynamic NMR and Theoretical Calculations

“…If the temperature has to be decreased well below -100°C, the samples have to be prepared in a more sophisticated way, with use of liquefied gases such as Me 2 O, [15] vinyl chloride, [16] propane, [17] propene, [18] Freons ® or mixtures of these (see Table 1). CHF 2 Cl/CHFCl 2 , 3:1 -182 [22] CHF 2 Cl/CHFCl 2 , 5:1 -190 [23] CHF 2 Cl/CHFCl 2 /CF 2 Cl 2 , 3:1:1 -170 [24] CHF 2 Cl/CHFCl 2 /CHF 3 , 5:1:1 -188 [25] CHF 2 Cl/CHFCl 2 /CHF 3 , 3:1:1 -182 [26] CCl 2 F 2 /CBrF 3 , 4:1 -157 [27] CF 2 Cl 2 /CBrF 3 , 2:1 -166 [28] CHFCl 2 /CCl 2 F 2 , 1:1 -165 [29] CHF 2 Cl/CHFCl 2 , 1:1 -174 [30] CHCl 2 F/CH 2 =CHCl, 6:1 -160 [31] Me 2 O/THF, 3:1 -140 [32] THF/Et 2 O, 3:2 -135 [32] CHF 2 Cl/CDFCl 2 , 3:1 -171 [33] CH 2 =CHCl/CS 2 , 4:1 -131 [34] CH 2 =CHCl/CS 2 , 3:2 -132 [34] CH 2 =CHCl/CHFCl 2 , 5:2 -152 [35] CD 2 Cl 2 /[D 8 ]toluene, 1:1 -120 [36] The use of hydrogen-containing solvents is often impractical because of their very strong signals, which can overlap with the signals of the dilute solute. Freons ® , in contrast, either do not show any signal in the proton spectra (CBrF 3 , CF 2 Cl 2 ), or only give a signal in the aromatic region of the spectrum (CHFCl 2 , CHF 2 Cl, CHF 3 ) and are also quite good solvents even at very low temperatures.…”

Analysis on biological importance of antiseptic drug, O-Benzyl hydroxylamine, by the application of spectroscopic and theoretical tools

“…The chemical reactivity mechanism of the chemical compound is formulated with respect to the chemical shift regulated in the core as well as ligand merged carbons and their related hydrogens [21]. Usually, the chemical reaction path can be identified through the core carbons due to the charge dislocation take place around the ligand groups are added to the appropriate places in the compound [22]. The chemical mechanism for generating the useful drug activity in the chemical species is setup by the adopting atoms or molecules with the base compound.…”