DFT study of the substituent cross-interaction effects on the conformation of substituted N-benzylideneanilines – Models of liquid crystal forming compounds: Use of 13C NMR chemical shift of the CN Carbon as a tool to predict the conformation of the molecule

Comparison of the substituent effects on the (13) C NMR with the (1) H NMR chemical shifts of CH=N in substituted benzylideneanilines

Fifty-two samples of substituted benzylideneanilines XPhCH=NPhYs (XBAYs) were synthesized, and their NMR spectra were determined in this paper. Together with the NMR data of other 77 samples of XBAYs quoted from literatures, the (1) H NMR chemical shifts (δH (CH=N)) and (13) C NMR chemical shifts (δC (CH=N)) of the CH=N bridging group were investigated for total of 129 samples of XBAYs. The result shows that the δH (CH=N) and δC (CH=N) have no distinctive linear relationship, which is contrary to the theoretical thought that declared the δH (CH=N) values would increase as the δC (CH=N) values increase. With the in-depth analysis, we found that the effects of σF and σR of X/Y group on the δH (CH=N) and the δC (CH=N) are opposite; the effects of the substituent specific cross-interaction effect between X and Y (Δσ(2) ) on the δH (CH=N) and the δC (CH=N) are different; the contributions of parameters in the regression equations of the δH (CH=N) and the δC (CH=N) [Eqns and 7), respectively] also have an obvious difference.

Substituent effects on the UV spectra of extended benzylidene anilines p-X-PhCH=NPhCH=CHPh-p-Y

Benzylidene anilines with p-substituted styryl groups substituted on the aniline ring, p-X-PhCH=NPhCH=CHPh-p-Y (X=NMe2, OMe, Me, H, Cl, F, CN, or NO2; Y=NMe2, OMe, Me, H, Cl, or CN) have been studied photochemically in ethanol. The substituent effects in the title compounds are more similar to p-X-PhCH=NPh-p-Y than p-X-PhCH=CHPh-p-Y. The introduction of styryl group to XBAY leads to a more planar geometry and a red shift of the maximum absorption wavelength. This can be described as a "styryl conjugation effect". Furthermore, a quantitative model has been established to correlate the UV maximum absorption wavenumbers of the title compounds and substituent parameters. The results help understand the substituent effects of conjugated compounds consisting of both benzylidene aniline and stilbene moieties.

Temperature-dependent Raman study of the smectic to nematic phase transition and vibrational analysis using density functional theory of the liquid crystalline system 4-decyloxy benzoic acid

Room-temperature Raman spectra of the thermotropic liquid crystalline system, 4-decyloxy benzoic acid (4DBA) have been recorded and the experimentally observed bands are assigned by density functional theory (DFT) for the first time. The C-O and C-C stretching and C-H in-plane bending modes of the phenyl ring and C=O stretching modes of the -COOH group are the marker bands for the smectic (S) --> nematic (N) and nematic (N) --> isotropic (I) transitions for this system. The temperature-dependent Raman spectra for these bands in the heating cycle clearly characterize the S-->N and the N-->I transition over a range <1 degree C, which is much better than the earlier range of 23 degrees C for S-->N and 26 degrees C for the N-->I transition. The approximately 773, approximately 807, approximately 881, and approximately 1146 cm(-1) bands disappear, whereas a band at approximately 830 cm(-1) appears at the S-->N transition. The relative intensity of the approximately 1257 and approximately 1280 cm(-1) bands distinguishes the three phases, namely smectic, nematic, and isotropic, in 4DBA. The variation of line width and peak wavenumber of the approximately 1128 and approximately 1168 cm(-1) bands also clearly shows the two transitions. The molecular reorientation at the transition and the effect of local fields present in the liquid crystalline mesophases are also briefly discussed on the basis of changes in intensity, linewidth and peak wavenumber with temperature.