The strength of aggregation in PdII, Nin, ZnII, and CdII metalloporphyrins is shown by n.m.r. spectroscopy to depend upon interaction of the metal ion with the porphyrin .rr-system; within a selected series of 2,4-disubstituted deuteroporphyrin-IX dimethyl esters complexed with a constant metal ion the aggregation is further enhanced by the presence of electron-withdrawing substituents on the porphyrin periphery.

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The effect of substituents on rotation about the phenyl-carbon bond in substituted toluenes is reported and discussed in terms of steric and electronic interactions.CONFORMATIONAL preferences about an sp3-sp2 bond have

A method for the Monte Carlo simulation, by digital computer, of the evolution of a colliding and coagulating population of suspended particles is described. Collision mechanisms studied both separately and in combination are: Brownian motion of the particles, and laminar and isotropic turbulent shearing motions of the suspending fluid. Steady-state distributions are obtained by adding unit-size particles at a constant rate and removing all particles once they reach a preset maximum volume. The resulting size distributions are found to agree with those obtained by dimensional analysis (Hunt 1982).

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