Force fields carbocations

Basis Sets Correlation Consistent Sets Carbocation Force Fields Coupled-cluster Theory Enthalpies of Hydrogenation G2 Theory Heats of Formation Hyperconjugation NMR Chemical Shift Computation Structural Applications NMR Data Correlation with Chemical Structure Proton Affinities. 

Biological and Organic Molecules Anharmonic Molecular Force Fields Carbocation Force Fields Carbohydrate Force Fields CHARMM The Energy Function and Its Parameterization Force Fields A Brief Introduction Force Fields A General Discussion Force Fields CFF Force Fields MM3 GROMOS Force Field and OPLS Force Fields). The multitudinous issues related to achieving convergence will be discussed below. 

Carbocation Force Fields Carbocation Stabilities Comparison of Theory and Experiment Carbohydrate Force Fields Carbohydrates Conformational Analysis 1 Conformational Analysis 2 Conformational Analysis 3 Force Fields A Brief Introduction Force Fields A General Discussion Infrared Spectra Interpretation by the Characteristic Frequency Approach Natural Bond Orbital Methods Solvation Carbohydrates Transition States in Organic Chemistry Ab Initio. 

These structures were then used to generate the force fields and calculate the secondary /3-deuterium-d6 equilibrium isotope effects (EIEs) for the formation of the isopropyl carbocation (Table 30). Because the transition states for formation of the carbocation will be close to the structure of the carbocation, these KIEs should be excellent approximations of the maximum secondary /3-deuterium KIEs expected for the limiting SN1 solvolytic reaction. 

Since carbocations are structurally similar to ketones, they are discussed here. Schleyer s force field incorporates carbocation parameters, and Harris is exploring their application in conformational analysis (188). The calculated angles in a series of rigid polycyclic carbocations correlated well with ketone infrared frequencies (188a). The calculated relative stabilities among various conformers of tertiary cations of methylcyclohexane, methylcycloheptane, and methyl-cyclooctane do not contradict the limited MNR observations of these species at low temperature (188b). 

We present in Fig. 35 the structure (C symmetry) optimized at the MP2(full)/6-31G(d) level (this work). Recently, a large computational study has been published on benzyl and larger carbocations. It uses both the optimized force field MMP2 extended to carbocations and MP4sdq/6-31G(d)//MP2(full)/6-31G(d) calculations. It provides, inter alia, valuable estimates of standard heats of formation. In this case, the difference in stability between phenethyl and 4-methylbenzyl cations (1.7 by ab initio computations and 2.9 kcal mol by MMP2) is in good agreement with the experimental results in Ref. 51. Our own G2(MP2) results are presented in Table 9. 

Early Attempts to Parameterize Force Fields for Carbocations by Paul v, R. Schleyer and his School... 

Earlier force field programs parameterized for carbocations used separate atom types for cationic sp -carbons. This procedure is not necessary in this new method. Instead, cationic carbons are treated as normal sp -carbons. The new parameters are added to the sp -carbons depending on the r-electron densities of these atoms, calculated by the SCF routine of MMP2, and their chemical environments. 

The adamantyl cations are typical examples of localized carbocations with strong geometric distortions as a result of hyperconjugation. The chiral C2 structure of the 2-propyl cation is confirmed impressively by the force field method. 

Carbocation Stabilities Comparison of Theory and Experiment Force Fields A General Discussion Mixed Quantum-Classical Methods Molecular Mechanics Conjugated Systems. 

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