D. Muriel Hall

Steric effects of methoxy-groups in 2,2′-bridged biphenyls. Part I

The preparation of (–)-6,7-dihydro-1,11-dimethoxy-5H-dibenz[c,e]azepine-6-spiro-1′-piperidinium iodide starting from (+)-6,6′-dimethoxydiphenic acid is described. Its optical stability has been determined approximately. Methyl 6-methoxydiphenate has been prepared and used for the synthesis of monomethoxydibenzazepinium salts.

X-Ray crystal structures of 2,2′-bridged biphenyls with heterocyclic bridging rings: contraction in ring size on reduction

X-Ray crystal structure analysis confirms that two of the four tetrabenzo [b,d,h,j][1,6]diazacyclododecines previously investigated have 12-membered rings; there is a strong presumption that the other two have a similar structure. Three of the four compounds undergo (dimethylamino)borane reduction to the tetrahydro derivatives in a process shown by X-Ray analysis and/or n.m.r. spectroscopy to involve C–N bond breaking and ring contraction from 12- to seven-membered rings. The fourth compound is shown by X-ray analysis to retain its (presumed) 12-membered ring structure when the tetrahydro derivative is produced by catalytic hydrogenation.

2,2′-Bridged biphenyls with 12-membered heterocyclic bridging rings. Part 1. Tetrabenzo[b,d,h,j][1,6]diazacyclododecines

Four tetrabenzo[b,d,h,j][1,6]diazacyclododecines and their tetrahydro-derivatives have been prepared. 1H N.m.r. and u.v. spectroscopy are used to determine the geometry of the tetrabenzodiazadodecines. It is concluded that they have the EE configuration, with dihedral angles in the biphenyl moieties of 55–60° and with angles of twist about the ArC–CHN and ArN–NCH single bonds of 10–20 and 80–70° respectively. N.m.r. spectra in the presence of chiral lanthanide shift reagents show that at least two of the compounds are chiral.

Detection of enantiomers in dissymmetric biaryls with chiral shift reagents

Abstract Methoxycarbonyl groups in racemic biphenyls show separation of the methyl proton magnetic resonance signals in the presence of large amounts of chiral shift reagents.

Nuclear magnetic resonance spectra of azomethines. Part I. Benzylideneanilines

N.m.r. spectra of 28 azomethines of the type Ar1CHNAr2 have been measured in deuteriochloroform. Susbtituent and steric effects on the chemical shift of the aldimine proton are discussed. ortho-Substitution in the aldehyde ring has a deshielding effect on this proton whereas ortho-substitution in the amine ring is shielding. The CHN group causes a downfield shift of ca. 0.60 p.p.m. for aromatic protons ortho to the carbon.

X-Ray structural studies of stereoisomeric bi(14H-dibenzo[4,5:6,7][1,3]diazepino[2,1-a]isoindol-14-ylidene)s obtained from the reaction of 2,2′-diaminobiphenyl with o-phthalaldehyde

Reaction of 2,2′-diaminobiphenyl with o-phthalaldehyde yielded a number of products including two bi-(14H-dibenzo[4,5:6,7][1,3]diazepino[2,1-a]isoindol-14-ylidene)s, (A) and (B); each was converted on heating into a third isomer (D). The crystal structure of (A), and that of (D), as the solvated trifluoroacetate salt, were determined; (A), previously thought to be the trans-isomer, is in fact the cis-(R,R)/(S,S)-isomer (1a), a racemic compound, and (D) is the meso trans-(R,S)isomer (2b). Compound (B) is considered to be the racemic trans-(R,R)/(S,S)-isomer (2a). The crystal structures of (A) and (D) and the 13C n.m.r. and u.v. spectra of all three isomers are discussed.

The 9,10-dihydrophenanthrene structure as a source of liquid crystals: mesogenic behaviour and spectroscopic properties of 2-benzylideneamino-9,10-dihydrophenanthrenes

13 Azomethines have been prepared from 2-amino-9,10-dihydrophenanthrene by reaction with aromatic aldehydes. Those with p-alkoxy, p-cyano or p-phenyl substituents in the aldehydic ring have a nematic mesophase. U.v. spectra, 1 H and 13C n.m.r. spectra, and mass spectra of the series are discussed. Mass spectra show that ortho-substituents in the aldehydic ring substantially modify the fragmentation pattern.

Nuclear magnetic resonance studies of heterocyclic bridged biphenyls

Condensation reactions (a) between 1,2-diamines and biphenyl-2,2′-dicarbaldehyde or 9,10-phenanthraquinone and (b) between 2,2′-diaminobiphenyl and 1,2-diketones give polycyclic products with 5-, 6-, 7- and 8-membered heterocyclic rings, the n.m.r. spectra of which are discussed. Temperature-dependent signals for the methylene protons in the 15H-dibenzo[c,e]benzimidazo[1,2-a]azepines (2) and (3) show that these compounds are conformationally labile. The dibenzo[a,c]phenazines (4) and (5) and dibenzo[f,h]quinoxaline (6) show large downfield shifts (δca. 9·5) for some aromatic protons.

Steric effects of a nitro group on the optical stabilities of 2,2′-bridged and unbridged biphenyls

Quaternary azepinium salts have been prepared from 4- and 6-nitro-2,2′-bisbromomethylbiphenyl. No optical activity was observed among the compounds with the p-nitro group, but suitable salts derived from the o-nitro-compound showed mutarotation in solution at room temperature. Racemisation data for the azepinium picrate from a 6-nitrobiphenyl, in acetone, show that it has an unusually high Arrhenius parameter A. The energy barrier to racemisation is discussed in relation to that in similar bridged compounds, and some apparent discrepancies between polarimetric results and those obtained by n.m.r. spectroscopy are pointed out. A related unbridged bisquaternary salt has been prepared and obtained optically active. It is optically stable up to ca. 90°, but the very low specific rotation has so far prevented quantitative study of its racemisation.