P. Murray-Rust

Geometrical substituent parameters for benzene derivatives: inductive and resonance effects☆

Abstract A full set of geometrical parameters describing the effect of 21 substituents on the internal angles of the benzene ring has been derived by linear regression from many structural results. The parameters are shown to reflect the inductive and resonance effects of the substituents.

Iodine⋯X(O, N, S) intermolecular contacts: models of thyroid hormoneprotein binding interactions using information from the cambridge crystallographic data files

Abstract Automated methods were used to search the Cambridge Crystallographic Data Files for all compounds containing CI bonds that had CI⋯X(O, N, S) contact distances less than 3.55 A for O and for N, and less than 4.0 A for S. Analysis of these data from 86 crystal structures showed that the distribution of nucleophile (O, N, S) contacts to iodine is non-spherical with the highest density and the shortest contacts (e.g., I⋯O = 2.96 A) and CI ⋯ X angle, φ = 180°. These data suggest that, where possible, that donor group is arranged so that one of its lone pairs is directed toward the iodine atom. Because the thyroid hormones are the only active iodine-containing compounds, CI⋯X interactions were considered as possible contributros to enhanced protein binding affinity. In the crystal structure of the thyroxine—prealbumin complex there is a close contact between the proximal outer-ring iodine of thyroxine and the carbonyl oxygen of Ala-109A in the prealbumin backbone. The geometry of this interaction (I⋯O, 2.96 A, CI⋯O, 161°) is within the distribution of the iodine—oxygen interactions observed in this analysis, and suggests that this model can explain (in part) the unique role of iodine in the binding of the thyroid hormones to their specific binding proteins.

1,2-oxazine chemistry—II : The crystal and molecular structure of N-(p-carboxybenzyl)-tetrahydro-1,2-oxazine

Abstract The crystal structure of the title compound has been determined from X-ray diffractometer data by direct methods, and refined by full matrix least squares techniques to R = 0·057 for 1231 reflections. The crystals are monoclinic, space group C2/C, cell dimensions a = 1665, b = 987, c = 1443 pm, β = 107·37° and Z = 8. The conformation of the tetrahydro-1,2-oxazine ring is a chair with the N-substituent equatorial. There is evidence of significantly greater torsional angles around the N and O atoms than around the ring C atoms, showing the ring to be more puckered than cyclohexane. The hydrogen bond is between the acid group on one molecule and the ring nitrogen on its neighbour.

The structures of anhydrobonellin and bonellin, the physiologically active pigment from the marine echiuroid

The structure of anhydrobonellin (II) has been proposed by spectroscopic techniques and confirmed by single crystal X-ray diffraction. The relationship of (II) to bonellin is clear and thus the structure of bonellin is certain.

A novel thermal rearrangement of the 2-thiabicyclo[3,1,0]hex-3-ene system. The crystal and molecular structure of ethyl-2,4-dichloro-5-hydroxy-6-methylbenzoate

Abstract Thermal rearrangement of 1,3-dichloro-6-ethoxycarbonyl-2-thiabicyclo[3, 1, 0]hex-3-ene does not follow the anticipated course, but leads instead to ethyl-2,4-dichloro-5-hydroxy-6-methylbenzoate, whose structure has been confirmed by an X-ray crystal structure determination.

Conversion of clavulanic acid into thiadeoxa nuclear analogues

Abstract 1,4-Addition of sulphur nucleophiles to the diene ( 12 ) derived via the pen-2-em ( 5 ) from clavulanic acid provides the thiadeoxa analogues ( 14 – 15 ). X-ray analysis of the ester ( 14 ) shows the thermodynamically stable isomers to have the same relative stereochemistry as clavulanic acid.

A biogenetically significant cyclization of humulene-4,5-epoxide

Abstract Rearrangement of humulene-4,5-epoxide with boron trifluoride etherate leads to the formation of two tricyclic alcohols the structures of which are closely related to that of africanol; the X -ray structure of the p -bromobenzoate of one of the alcohols is reported.

Application of DNMR, group theory and molecular mechanics in the elucidation of the inversion process in the flexible molecule perhydrotetra-azapyrene

Abstract The inversion process in cis-10b,10c-perhydro-1H,6H-3a,5a,8a,10a-tetraazapyrene (1) has been investigated by 1H and 13C NMR. The free energy of activation is found to be 14.95 ± 0.2 kcal mole−1 at 45°. Application of group theoretical techniques led to a graph representing the essential symmetry properties of the potential energy surface for conformational change. The energies of intermediates on this graph were then estimated using molecular mechanics calculations. This combined approach suggests that the total inversion proceeds via a conformation of C2v symmetry with two non-chair piperazine rings, calculated to be 6.8 kcal mole−1 less stable than the ground state conformation (C2 symmetry).

1-Phenyl-2,3-diazacycl[3,2,2]azine, a new 10-π electron system. Involvement of 3,5-didehydroimidazo[1,5-a]pyridine?

Abstract 3-Ethylthioimidazo[1,5-a]pyridine reacts with butyl lithium followed by benzonitrile to give the new 10-π electron system, 1-phenyl-2,3-diazacycl[3,2,2]azine, possibly via 3,5-didehydroimidazo[1,5-a] pyridine.

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol and the conformation of bicyclo[3.3.3]undecane (manxane)

Abstract The crystal structure of bicyclo [3.3.3]undecane-1,5-diol has been determined. It is monoclinic, P2 1 / c , a = 12.99(2), b = 14.16(2), c = 12.50(1)A,β = 112.42(2)°, with two independent molecules in the asymmetric unit. One of these is disordered, but the other has almost exact C 3h symmetry and its conformation and precise molecular geometry agree well with previous calculations by molecular mechanics. The molecule shows considerable angle strain, having bridge angles in the range 118–121°