H. G. Ff. Roberts

Uncoupled Hartree–Fock Calculations of the Ring‐Current Contribution to the Magnetic Susceptibilities of Conjugated Molecules

Uncoupled Hartree–Fock perturbation theory is used to compute the ring‐current contributions to the magnetic susceptibilities of several conjugated hydrocarbons. In the usual form of the perturbation theory this leads to an origin dependent result, but when corrections are included this origin dependence is removed. The final results agree very well with those calculated using the more complicated coupled Hartree–Fock method, and, when empirical values are used for the local contributions to the susceptibility, the theoretical values for the components, the mean value, and the anisotropy of the susceptibility are in excellent agreement with experiment.

The calculation of chemical shifts in conjugated molecules

Within the context of pi-electron theory an expression for the proton chemical shifts in conjugated molecules is derived via a current density approach. Using London integral approximations the method is applied to benzene and naphthalene. Provided a particular form of the London Approximation is used, theoretical values in good agreement with experiment are obtained.

Improved chemical shift calculations in conjugated molecules

Abstract Calculations are presented of the ring current contribution to the chemical shifts in benzene, naphthalene and anthracene. Some of the usual simplifying assumptions are not made and numerical integration has to be performed. The results obtained are thereby greatly improved while remaining independent of choice of origin. A subsequent analysis of the bond contributions to the shifts highlights the inaccuracies involved in most previous calculations.

Ring-current contributions to the proton magnetic resonance of aromatic hydrocarbons with hexagonal geometry

Recent improvements in the theoretical determination of ring-current contributions to the proton shifts in aromatic molecules are discussed in a practical framework in the case of benzenoid hydrocarbons. Integral values are tabulated in a form which ensures that the method is simple to apply.

On the chemical shifts in conjugated systems

The calculation of the ring-current contribution to the proton chemical shifts in conjugated systems using uncoupled Hartree-Fock perturbation theory is improved by the inclusion of origin variation in the expression for the vector potential.

The calculation of chemical shifts in conjugated molecules: II. A semi-rigorous calculation of the pi-electron contribution to the magnetic properties of benzene

Calculations are presented of the non-local pi-electron (ring current) contribution to the magnetic anisotropy of benzene and to the chemical shift experienced by an attached proton. The usual London Approximation (to simplify the integral evaluation) is not made, and the method thereby permits of a more detailed analysis of this approximation than has hitherto been possible.

Uncoupled Hartree-Fock calculations of the ring current properties of some heterocyclics

It is shown that uncoupled Hartree-Fock perturbation theory may be successfully applied to the determination of the ring current properties of heterocyclics.

Orbital transformation and perturbation theory

Abstract The first order perturbative correction to a single determinant wave function is shown to be invariant in form to a unitary transformation of the molecular orbitals both for the case of (a) electron correlation treated as a perturbation and (b) external perturbations. The implications of this are briefly discussed.