Lawrence D. Colebrook

Restricted Internal Rotation in 1-Arylhydantoins, 3-Arylhydantoins, and 3-Aryl-2-Thiohydantoins: Reversal of the Effective Sizes of Methyl and Chlorine

In 1-arylhydantoins an o-methyl group is effectively larger than an o-chloro substituent in restricting rotation about the aryl-C—N bond, whereas in 3-arylhydantoins and 3-aryl-2-thiohydantoins the reverse order of sizes is observed. This difference is attributed to repulsion between the chlorine atom and a carbonyl oxygen atom in the torsional transition state of the 3-aryl compounds.

Synthesis of a novel 1,4-bridged calix[8]arene “Host” cavity

A conformationally stable, acridone-based linker (1) was synthesized and attached to p-tert-butylcalix[8]arene (2) to form the novel 1,4-bridged calix[8]arene derivative 3. The structural assignment of 3 was based on its MS and high-field NMR data and supported by molecular modeling calculations.

Conformational preferences in some aryl substituted heterocyclic compounds exhibiting restricted internal rotation about C–N bonds

X-Ray studies of the thermodynamically less stable (in solution) diastereoisomeric rotational isomer of 3-(2-bromophenyl)-5-methyl-2-thiohydantion (II) show that the bromine atom is transoid to the 5-methyl group.

Estimation of the spin–lattice relaxation time constants of low molecular weight solutes in dilute complex aqueous solutions: application to urinary metabolites

Proton spin–lattice relaxation rate constants (T1 values) of some selected urinary metabolites were analysed extensively by two different least‐squares minimization procedures, based on the simplex and the Marquardt–Levenberg algorithms. Comparative multiplicate analysis under different experimental conditions using laboratory solutions of some of the urinary metabolites was employed in addition to direct measurements on human urine samples. The T1 values estimated for most of the metabolites by the two methods agreed to within 10–15%.