Liversidge Research Lecture, delivered before the Royal Society of New South Wales, 14 October, 1992. Reproduced by permission of the Royal Society of New South Wales from J. Proc. Roy. Soc. N.S.W., 1993, 126, 1354-143. Over the last 10 years our group has carried out two parallel experimental investigations in physical-organic chemistry. first one dealt with the development of a new experimental parameter for the determination of the π-bond order of the carbon-carbon double bond and the utilisation of this new parameter in the determination of the ground-state electronic structures of some unsaturated systems. The second investigation dealt with the limitations of a previously proposed (Bott, Field and Sternhell, 1980) semi-quantitative treatment for predicting the severity (energy penalty) of repulsive non-bonded interactions from purely structural parameters.

The sections in this article are 1 NMR Physics 2 NMR Instrumentation and Techniques 3 Interpretation of NMR Spectra 4 Biographical Sketch

Methyl-silicon bond cleavage of tetramethylsilane occurs with aryllead(IV) tricarboxylates in trifluoroacetic acid to produce aryl(methyl)lead(IV) bistrifluoroacetates in high yield. An extension of the study to tetraalkylstannanes has shown that alkyl-tin cleavage by lead(IV) carboxylates proceeds even in chloroform, while a detailed study of the reactions of lead tetraacetate with tetraalkylstannanes indicated the reaction to be an electrophilic cleavage rather than one involving an electron transfer mechanism.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectrophilic Substitution in Naphthalene: Kinetic vs Thermodynamic ControlLeslie D. Field , Sever Sternhell , and Howard V. Wilton View Author Information The University of Sydney, Division of Organic Chemistry, Sydney, N.S.W. 2006, AUSTRALIACite this: J. Chem. Educ. 1999, 76, 9, 1246Publication Date (Web):September 1, 1999Publication History Received3 August 2009Published online1 September 1999Published inissue 1 September 1999https://pubs.acs.org/doi/10.1021/ed076p1246https://doi.org/10.1021/ed076p1246research-articleACS PublicationsRequest reuse permissionsArticle Views1361Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Aromatic compounds,Hydrocarbons,Kinetics,Nuclear magnetic resonance spectroscopy,Thermodynamics Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTHighly Efficient Chirality Inducers Based on Steroid-Derived 2,6,9-Trioxabicyclo[3.3.1]nonanesJenny J. Park, Sever Sternhell, and Simone C. VonwillerView Author Information School of Chemistry, University of Sydney, NSW, 2006, Australia Cite this: J. Org. Chem. 1998, 63, 19, 6749–6751Publication Date (Web):September 2, 1998Publication History Received30 March 1998Published online2 September 1998Published inissue 1 September 1998https://pubs.acs.org/doi/10.1021/jo980572qhttps://doi.org/10.1021/jo980572qbrief-reportACS PublicationsCopyright © 1998 American Chemical SocietyRequest reuse permissionsArticle Views104Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Chirality,Molecular structure,Oligomers,Power,Substituents Get e-Alerts

Treatment of naphthalene and biphenyl with alumina and hydrogen in a vibratory mill for about 5h at ambient temperature gives up to 75 % and 15 % of tetralin and phenylcyclohexane respectively. This suggests that the previously reported(1) disproportionation of naphthalene and biphenyl to give tetralin and phenylcyclohexane by analogous treatment under nitrogen proceeds at least partially by a step involving molecular hydrogen. However, these observations are not general because identical mechanical treatment of trans-stilbene under hydrogen gave less bibenzyl than under nitrogen. (C) 1997 Elsevier Science Ltd. All rights reserved.

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTHighly Efficient Chirality Inductors Based on (5RS,8RS)-trans-5,6,6a,7,8,12b- Hexahydrobenzo[c]phenanthrene-5,8-diolJulie Cheung, Leslie D. Field, and Sever SternhellView Author Information Department of Organic Chemistry, University of Sydney, Sydney NSW, Australia 2006Cite this: J. Org. Chem. 1997, 62, 20, 7044–7046Publication Date (Web):October 3, 1997Publication History Received10 March 1997Published online3 October 1997Published inissue 1 October 1997https://doi.org/10.1021/jo9704319Copyright © 1997 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1117Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (112 KB) Get e-AlertsSUBJECTS:Chemical structure,Genetics,Molecular structure,Power,Solution chemistry Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTHighly Efficient Chirality Inductors Based on (5RS,8RS)-trans-5,6,6a,7,8,12b- Hexahydrobenzo[c]phenanthrene-5,8-diolJulie Cheung, Leslie D. Field, and Sever SternhellView Author Information Department of Organic Chemistry, University of Sydney, Sydney NSW, Australia 2006Cite this: J. Org. Chem. 1997, 62, 20, 7044–7046Publication Date (Web):October 3, 1997Publication History Received10 March 1997Published online3 October 1997Published inissue 1 October 1997https://doi.org/10.1021/jo9704319Copyright © 1997 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1117Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (112 KB) Get e-AlertsSUBJECTS:Chemical structure,Genetics,Molecular structure,Power,Solution chemistry Get e-Alerts

Reduction of trans-5,5,6a,7,8,12b-hexahydro-1,12-dimethylbenzo[c]phenanthrene-5,8-dione (1, R(1) = R(4) = H, R(2) = R(3) = CH(3)) with lithium aluminum hydride yielded stereoselectively (5RS,8RS)-trans-5,6,6a,7,8,12b-hexahydro-1,12-dimethylbenzo[c]phenanthrene-5,8-diols 2, X = H. These diols proved to be configurationally stable chiral molecular templates capable of straightforward modification by attachment of molecular elements of different length and kind. The structures of the diacetate 2, X = COCH(3), and (5R,8R)-(-)-trans-5,6,6a,7,8,12b-hexahydro-1,12-dimethylbenzo[c]phenanthrene-5,8-diyl di-p-bromobenzoate (2a, X = p-BrC(6)H(4)CO), as well as the absolute configuration of the latter were obtained by X-ray crystallography.

Aromatic hydrocarbons (biphenyl, naphthalene, anthracene and phenanthrene) were subjected to ball milling (SPEX® 8000) with approximately ten-fold weight of inorganic materials (alumina or silica). After about 24 h all of the hydrocarbons were converted largely to carbon (graphite), but at intermediate stages disproportionation products (tetralin, phenylcyclohexane, bicyclohexyl, 9,10-dihydroanthracene, 1,2,3,4-tetrahydroanthracene, 1,2,3,4,4a,9,9a,10-octahydroanthracene, 1,2,3,4,5,6,7,8-octahydroanthracene, 9,10-dihydrophenanthrene, 1,2,3,4-tetrahydrophenanthrene, 1,2,3,4,4a,9,9a,10-octahydrophenanthrene, 1,2,3,4,5,6,7,8-octahydrophenanthrene) were also obtained in significant yields.

To assess the utility of a new, rapid, economical procedure that may prove valuable in cervical screening, Fourier transform infrared (ir) spectroscopy was performed on 25 cervicovaginal lavage specimens from women referred for colposcopy on the basis of a cytological abnormality detected on their Pap smear and whose lavage specimen was positive for human papillomavirus. Of the 18 classed as CIN I or less by histopathology, 11 showed band frequencies that deviated only slightly from spectra that characterize normal cervical cells and 3 of 5 "atypia" specimens had spectra identical to normal. Two of 3 classed as CIN II had spectra only slightly more abnormal to these 11. In the case of 2 graded as CIN I, several bands were similarly altered in the direction of the pattern seen for 4 CIN III specimens. A further CIN I sample gave a spectrum that was even further shifted toward the latter and the remaining CIN I sample had a pattern that matched the 4 CIN IIIs. The most obvious change in each of the CIN IIIs was an additional peak at 972 cm-1 and this has been suggested as a key indicator for malignancy. One of the 3 CIN IIs had this peak. Other characteristic spectral changes were seen as well in the CIN III samples. High-risk HPV18 was present in 3 of the CIN III samples, as well as in one specimen classed as atypia, but having an abnormal ir spectrum. Low-risk HPV 6 or 11 was seen along in samples with a normal or slightly abnormal ir spectrum, but never in those that showed an ir pattern that was abnormal. The current study has therefore shown complete concordance between ir spectral findings and histopathology result in the case of CIN III specimens, but less precise matching for other grades of CIN. The spectral differences revealed by ir spectroscopy are likely to characterize molecular abnormalities in cervical cells during progression to cancer and may therefore have potential in assisting with clinical decision making. More studies will, however, be required to establish the place of this technique in cervical screening.

Two lipophilic tetradentate ligands, 5,5′-di-t-butyl- and 5,5′-dihexyl-2,2′-bipyrimidine, were prepared via either Ullmann or nickel(0)-promoted reactions in low but useful yields. Approaches towards the synthesis of lipophilic ligands based on 2,2′-biimidazole, namely 4,4′,5,5′-tetrabutyl-2,2′-biimidazole (from decane-4,5-dione) and various 4,4′,5,5′-tetra( arylamino )- 2,2′-biimidazoles (from 4,4′,5,5′-tetrabromo-2,2′-biimidazole and arylamines), and a 2,2′- bibenzimidazole , 5,5′,6,6?-tetra( octyloxy )-2,2′-bibenzimidazole (from N,N′- bis [4,5-di( octyloxy )-2-nitrophenyl] oxamide ), were uniformly unsuccessful for preparing the 2,2′-biheteroaryl compounds.

The previously established 1H n.m.r. method of probing bond order1 has been used to show that electron-donating (+R) substituents at C2 of pyridine cause significant ground-state polarization of the heteroaromatic system. This has led to a new and independent method of estimating the substituent resonance parameter (σR ).

4J(Me - C-C - II) = 4J(OB), the spin-spin coupling constant over four formal bonds between methyl protons and a proton bonded to an sp2 carbon, previously established 9-17 as a probe for bond order, was determined for 6-methyl-1,4-dihydro-1,4-methanonaphthalene (1) and for a number of reference compounds 2-5. Self-consistent field (SCF) calculations at the 3-21G level for 1-4 predict partial bond fixation in the benzene ring for all molecules in the sense predicted by interpretation of previously-reported photoelectron spectra of closely-related molecules. 31,32 The benzene moiety pi-bond orders were calculated from pseudominimal basis sets obtained by contraction of the double-zeta basis. Two types of bond order, one obtained with a nonorthogonal and the other with a Lowdin-orthogonalized pseudominimal basis, are reported. It is found that, as for planar compounds, there is a linear relationship between either type of bond order and 4J(OB) However, the correlation coefficients are considerably smaller, owing partly to the small size of the sample and partly to the fact that the range of values is much smaller than in comparisons for planar molecules, 9-11 so that the importance of contributions of terms other than the Fermi contact term and deviations from the McConnell ''average energy'' approximation 44 may be significant. The partial bond fixation is attributed to the effects of sigma-through-bond coupling to the attached framework, and, in the case of 1 and 2, additional coupling to the sigma-linked pi-bonding orbital of the ethylenic group. This constitutes independent NMR evidence for orbital interaction between sigma-linked pi-orbitals.

The allylic interproton spin-spin coupling constant, 4J(CH3C = CH) (4J(Me,H)), which has previously been established as a sensitive probe of bond order, was measured in a range of free-base porphyrins and metallo-2-methylporphyrins. The measured room temperature 4J(Me,H) values in a range of substituted porphyrins ((1.02-1.45) +/- 0.03 Hz) were correlated to the pi-bond order of the four beta-beta pyrrolic linkages of the porphyrins. In 2-methyl-5,10,15,20-tetraphenylporphyrin (2) (average 4J(Me,H) 1.19 +/- 0.03 Hz), the bond order across the two beta-beta' pyrrolic bonds involved in the aromatic delocalization pathway in each of the isolated tautomers, 2a and 2b, is considerably higher than the bond order in toluene and pyrrole and corresponds to a Pauling bond order of ca. 0.76 or a self-consistent field (SCF) bond order of ca. 0.66. The bond order across the two beta-beta' pyrrolic bonds not involved in the delocalization pathway is similar to that found in "pure" double bonds, and these bonds may be regarded as essentially fully localized carbon-carbon double bonds. The room-temperature 4J(Me,H) values in methylnitroporphyrins 5-10 ranged from 1.12 to 1.45 Hz and reflect the relative tautomer populations. Ground-state structural information about bond delocalization between the beta- and beta'-pyrrolic positions of metalloporphyrins was similarly obtained from measurement of the 4J(Me,H) values for a series of 2-methylporphyrins (15-18) (M = Mg, Zn, Pd, Ni). The 4J(Me,H) values lie in the range 1.14-1.21 Hz, i.e., a Pauling bond order of ca. 0.76 which clearly rules out the possibility of a 16-atom dianion structure with localized double bonds at the four beta-beta' pyrrolic positions as has been previously been proposed for a magnesium(II) porphyrin (Spangler, D.; Maggiora, G. M.; Shipman, L. L.; Christoffersen, R. E. J. Am. Chem. Soc. 1977, 99, 7470). Bond orders were determined on two free-base methylnitroporphyrins and their corresponding zinc(II) chelates. In the free-base methylnitroporphyrins 8 and 9, the nitro group causes bond fixation such that one 18-pi tautomer predominates over the other tautomeric form. In contrast, no such bond fixation was detected in the zinc chelates, 19 and 20, respectively. These findings indicate that the bond order at all beta-beta' pyrrolic positions in metalloporphyrins is intermediate between that of aromatic and localized bonds.

The previously established n.m.r. method for estimating mobile bond orders was applied to the investigation of ground-state polarization of benzene derivatives with ortho or para pairs of +R/-R substituents, naphthalene and five heteroaromatic systems (furan, thiophen, pyrrole, quinoline and pyrazole). Evidence for significant ground-state polarization which is solvent-independent was found in a number of these systems, especially benzene, pyrrole and pyrazole.

A study of the position of tautomeric equilibrium in deuteroporphyrin IX methyl ester (3) and monosubstituted derivatives 4-7 using variable-temperature studies on the N,N-dideuteriated derivatives 8-12 is reported. The kinetic isotope effect on the prototropic exchange process is sufficiently large to allow the convenient observation of the individual tautomers by H-1 NMR spectroscopy. As in the case of 2-substituted 5,10,15,20-tetraphenylporphyrins 1, the position of the tautomeric equilibrium in deuteroporphyrin derivatives is dependent on the substituent pattern on the porphyrin outer periphery. For the isomeric acetylporphyrins, 8-acetyldeuteroporphyrin IX dimethyl ester (9) and 3-acetyldeuteroporphyrin IX dimethyl ester (10), the acetyl group is the major influence in determining tautomer stability, i.e., both porphyrins are essentially one tautomer (> 85% at 298 K) in which the acetyl group is not involved in the aromatic delocalization pathway. The more stable tautomer (59% at 298 K) of 3-(1-hydroxyethyl)deuteroporphyrin IX dimethyl ester (11) is that in which the hydroxyethyl substituent is directly substituted on the aromatic pathway. The vinylporphyrin (12) exists predominantly (56% at 298 K) as the tautomer in which the vinyl group is substituted on the beta-beta pyrrolic bond remote from the aromatic delocalization pathway. Conjugation of the vinyl group in 12 and the carbonyl group in the acetylporphyrins 9 and 10 with the beta-beta pyrrolic double bond probably contributes to the overall stability of the major tautomer of these porphyrins. This work serves to further emphasize that all nonsymmetric free-base porphyrins are necessarily a mixture of two tautomers of different energies which should be taken into account in interpreting the physical and chemical properties of these systems.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

(I) C 16 H 14 O 2 cristallise dans P1 avec a=14,844, b=14,960, c=15,464 A, α=59,34, β=62,84, γ=62,00°, Z=8; affinement jusqu'a R=0,043. (II) C 12 H 12 O 2 cristallise dans C21C avec a=12,297, b=18,849, c=11,816 A, β=119,06°, Z=8; affinement jusqu'a R=0,034. Dans les deux composes, les atomes O 4 , des groupes methoxy sont tres proches. Ceci induit une deformation legere du naphtalene, mais importante du phenanthrene. Compare aux autres phenanthrenes disubstitues en 4,5, cet effet montre qu'il y a interaction entre le groupe methyl du methoxy et le compose tricyclique. Cependant, les longueurs des liaisons ne sont pas modifiees. Les distances O...O sont identiques dans les deux composes, ce qui est anormal pour le phenanthrene, mettant ainsi en evidence l'anisotropie des interactions O...O