Factor Analysis, Target Factor Testing and Model Designing of Aromatic Solvent Effect of the Formyl Proton Nuclear Magnetic Resonance Chemical Shift in Para substituted Benzaldehydes
Ghazwan F. Fadhil
DOI : 10.3844/ajassp.2010.24.32
American Journal of Applied Sciences
Volume 7, Issue 1
Problem statement: The variations of formyl proton Chemical Shifts (CS) of p-substituted benzaldehydes in aromatic solvents were investigated. The validity of several physical solvent and empirical solvent scales was examined. Also, to predict dipolarity-polarizability (π*) solvent scale for some aromatic solvents. Model designing was also achieved to rationalize the aromatic solvent effect on the formyl proton CS. Approach: The previously recorded formyl proton CS for p-X- benzaldehydes, with X were NMe2, OMe, OC3H7, H, Br, CHO and NO2 in benzene, toluene, p-xylene, m-xylene and mesitylene were subjected to Factor Analysis (FA). Target Factor Testing technique (TFT) was performed for several solvent scales namely: Unity, the intrinsic aromatic solvent induced shift of TMS (IASISTMS), f(n), f(d), (n2-1)/(n2+2), (d-1)/(d+2), ET(30) and π*. Iterative TFT was applied to predict unmeasured (π*) solvent scale for ethyl benzene, n-butyl benzene, sec-butyl benzene, tert-butyl benzene and isopropyl benzene. Results: It has been found that two factors were responsible for the variation in the formyl proton CS. The unity, f(n), (n2-1)/(n2+2), IASISTMS, ET(30) and π* were real factors. Model designing of the formyl proton CS in benzene, toluene, p-xylene, m-xylene and mesitylene were achieved. The models with lowest root mean square error (RMSE) have shown that Unity is a consistent term. The other term was either IASISTMS or π*. Iterative TFT predicted new π* values for ethylbenzene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene and isopropylbenzene respectively. Conclusion: FA has revealed that two real factors are responsible for the variation of formyl CS in benzene, toluene, p-xylene, m-xylene and mesitylene solvents. TFT has shown to be a powerful technique in predicting new values of the π* solvent scale. Model designing for the formyl proton CS have revealed that the IASISTMS, π* and Unity are the best empirical solvent scales and were better than any physical solvent scales in reproducing the formyl CS. The IASISTMS reflects the dipolarity-polarizabilty of the aromatic solvent. The cofactor of the solvent scale was found to correlate with the σp+ substituent parameter.
© 2010 Ghazwan F. Fadhil. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.