Substituent Cross-Interaction Effects on the Electronic Character of the CN Bridging Group in Substituted Benzylidene Anilines − Models for Molecular Cores of Mesogenic Compounds. A13C NMR Study and Comparison with Theoretical Results
- 17 March 2006
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 71 (8), 3141-3148
- https://doi.org/10.1021/jo0600508
Abstract
13C NMR chemical shifts δC(CN) were measured in CDCl3 for a wide set of mesogenic molecule model compounds, viz. the substituted benzylidene anilines p-XC6H4CHNC6H4p-Y (X = NO2, CN, CF3, F, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, F, Cl, H, Me, MeO, or NMe2). The substituent dependence of δC(CN) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on δC(CN): electron-withdrawing substituents cause shielding, while electron-donating ones behave oppositely, the inductive effects clearly predominating over the resonance effects. In contrast, the aniline substituents Y exert normal effects: electron-withdrawing substituents cause deshielding, while electron-donating ones cause shielding of the CN carbon, the strengths of the inductive and resonance effects being closely similar. Additionally, the presence of a specific cross-interaction between X and Y could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the CN group to the electronic effects of the benzylidene or aniline ring substituents. Electron-withdrawing substituents on the aniline ring decrease the sensitivity of δC(CN) to the substitution on the benzylidine ring, while electron-donating substituents have the opposite effect. In contrast, electron-withdrawing substituents on the benzylidene ring increase the sensitivity of δC(CN) to the substituent on the aniline ring, while electron-donating substituents act in the opposite way. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects). The present NMR characteristics are discussed as regards the computational literature data. Valuable information has been obtained on the effects of the substituents on the molecular core of the mesogenic model compounds.Keywords
This publication has 37 references indexed in Scilit:
- Synthetic protocols, molecular polarity, and 13C NMR correlations for 1-aryl- and 1-diarylmethylidene-1H-cyclopropa[b]naphthalenesOrganic & Biomolecular Chemistry, 2004
- Ab initio study of phenyl benzoate: structure, conformational analysis, dipole moment, IR and Raman vibrational spectraJournal of Molecular Modeling, 2003
- Remote Substituent Effects on N−X (X = H, F, Cl, CH3, Li) Bond Dissociation Energies in Para-Substituted AnilinesThe Journal of Organic Chemistry, 2002
- BRIDGE EFFECT OF THE C&dbnd;N BOND AND LONG DISTANCE ELECTRONIC EFFECTS OF ELECTRON-DONOR (D) SUBSTITUENTS ON N-(4-D-BENZYLIDENE)-4-NITROANILINES AND N-(4-NITROBENZYLIDENE)-4-D-ANILINESpectroscopy Letters, 2002
- An analysis of substituent effects on 1H and 13C NMR parameters of substituted furans. Linear free energy relationships and PM3 semiempirical calculationsJournal of the Chemical Society, Perkin Transactions 2, 1998
- Interpretation of substituent‐induced chemical shifts in 13C NMR spectra of 2‐substituted norbornadienes. Influence of homoconjugationMagnetic Resonance in Chemistry, 1995
- Liquid crystals of 4-octyloxy-N-(benzylidene)aniline derivatives bearing trifluoromethyl or trifluoromethoxy end groupsLiquid Crystals, 1995
- A survey of Hammett substituent constants and resonance and field parametersChemical Reviews, 1991
- Multiple Substituent Effects on 13C Chemical Shifts of N-Benzylideneanilines. Evidence for Substituent–Substituent Interactions and Their Implications of Conformational Changes with SubstituentsBulletin of the Chemical Society of Japan, 1985
- Long range substituent‐induced chemical shifts in the 13C NMR spectra of N‐benzylidenebenzylaminesMagnetic Resonance in Chemistry, 1978