“…The Δ E min values for these amines (for each, Δ E min = E min of the transition state − E min of the ground state) represent approximately the strain of the transition state relative to the ground state. For 1a − 8a the Δ E min values correlate well with the experimental Δ G ⧧ values ,,,,,, for these amines and are in all cases 76−101% of these experimental barriers (see Table ). Thus, the relative strain between the transition and ground states of polycyclic tertiary amines is the main factor in determining the rate of nitrogen inversion for these compounds.…”
Section: Discussionsupporting
confidence: 70%
“…For instance, the E sid vs Δ G ⧧ plot is linear (see Figure ; a = 0.19 and b = 10.5) for methyl isopropylamines 11b,c,f (these compounds were chosen in order to confine the data to one source 15 ). Furthermore, we used the barriers, measured by Nelsen , for N -methyl- and N -ethylamines 3a,b , to attain Δ G ⧧ / E sid dependence for 9-alkyl-9-azabicyclo[3.3.1]nonanes and found that this plot (B in Figure ; a = 0.69 and b = 27.6) is nearly parallel to the plot for azanorbornanes. 2 A linear dependence of the height of the N-inversion barriers (at 220 K) on the relative strain for 7-alkyl-7-azabicyclo[2.2.1]heptanes 1a − d , f (A: Δ G ⧧ = −0.84 E sid + 51.4), 9-alkyl-9-azabicyclo[3.3.1]nonanes 3a , b (B: Δ G ⧧ = −0.69 E sid + 27.6), and alkylmethylisopropylamines 11b , c , f (C: Δ G ⧧ = −0.19 E sid + 10.5).…”
The nitrogen inversion barriers for N-isopropyl-, N-butyl-, N-isobutyl-, and N-tert-butyl-7-azabicyclo-[2.2.1]heptanes were measured using dynamic NMR line shape analysis. These barriers as well as those for different bicyclic and tricyclic tertiary amines were analyzed Via the molecular mechanics method (MM3 force field). A new MM3 steric energy-based parameter, including the energy of substitution-induced disturbances (E sid ), is proposed for the estimation of relative strain among related compounds with one variable substituent. A linear relationship was found between N-inversion barriers and this parameter for 7-azabicyclo[2.2.1]heptanes with a -unbranched N-substituent, which allows an accurate prediction of the barrier values for these amines. For all polycyclic systems studied, the change of strain in the transition state relative to the ground state of the amine, simulated by MM3, makes up 76-106% of the experimental value of the corresponding N-inversion barrier. Among these amines some azabicycles ("bicyclic effect" systems) display the largest deviation (∼25%) from the experimental barrier value. From the point of view of the classical model, this deviation may be attributed to a bicyclic effect which would have an orbital origin.
“…The Δ E min values for these amines (for each, Δ E min = E min of the transition state − E min of the ground state) represent approximately the strain of the transition state relative to the ground state. For 1a − 8a the Δ E min values correlate well with the experimental Δ G ⧧ values ,,,,,, for these amines and are in all cases 76−101% of these experimental barriers (see Table ). Thus, the relative strain between the transition and ground states of polycyclic tertiary amines is the main factor in determining the rate of nitrogen inversion for these compounds.…”
Section: Discussionsupporting
confidence: 70%
“…For instance, the E sid vs Δ G ⧧ plot is linear (see Figure ; a = 0.19 and b = 10.5) for methyl isopropylamines 11b,c,f (these compounds were chosen in order to confine the data to one source 15 ). Furthermore, we used the barriers, measured by Nelsen , for N -methyl- and N -ethylamines 3a,b , to attain Δ G ⧧ / E sid dependence for 9-alkyl-9-azabicyclo[3.3.1]nonanes and found that this plot (B in Figure ; a = 0.69 and b = 27.6) is nearly parallel to the plot for azanorbornanes. 2 A linear dependence of the height of the N-inversion barriers (at 220 K) on the relative strain for 7-alkyl-7-azabicyclo[2.2.1]heptanes 1a − d , f (A: Δ G ⧧ = −0.84 E sid + 51.4), 9-alkyl-9-azabicyclo[3.3.1]nonanes 3a , b (B: Δ G ⧧ = −0.69 E sid + 27.6), and alkylmethylisopropylamines 11b , c , f (C: Δ G ⧧ = −0.19 E sid + 10.5).…”
The nitrogen inversion barriers for N-isopropyl-, N-butyl-, N-isobutyl-, and N-tert-butyl-7-azabicyclo-[2.2.1]heptanes were measured using dynamic NMR line shape analysis. These barriers as well as those for different bicyclic and tricyclic tertiary amines were analyzed Via the molecular mechanics method (MM3 force field). A new MM3 steric energy-based parameter, including the energy of substitution-induced disturbances (E sid ), is proposed for the estimation of relative strain among related compounds with one variable substituent. A linear relationship was found between N-inversion barriers and this parameter for 7-azabicyclo[2.2.1]heptanes with a -unbranched N-substituent, which allows an accurate prediction of the barrier values for these amines. For all polycyclic systems studied, the change of strain in the transition state relative to the ground state of the amine, simulated by MM3, makes up 76-106% of the experimental value of the corresponding N-inversion barrier. Among these amines some azabicycles ("bicyclic effect" systems) display the largest deviation (∼25%) from the experimental barrier value. From the point of view of the classical model, this deviation may be attributed to a bicyclic effect which would have an orbital origin.
“…After 40 min, more initiator and thiol (3 mol% of each) were added and heating was continued for a further 2 h. The solvent was removed by evaporation under reduced pressure and the residue was subjected to flash chromatography on silica gel (hexane eluent) to give 2-methyladamantane 2a (131 mg, 87%), mp 146-147 °C (lit. 6 mp 146-148 °C).…”
The deoxygenation of tertiary alcohols can be accomplished by heating their MOM ethers in the presence of a peroxide initiator and a thiol catalyst: the proposed radical-chain mechanism is supported by EPR spectroscopic studies.
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