Quantification and classification of substituent effects in organic chemistry: a theoretical molecular electrostatic potential study

Abstract

Substituent effects in organic chemistry are generally described in terms of experimentally derived Hammett parameters whereas a convenient theoretical tool to study these effects in π-conjugated molecular systems is molecular electrostatic potential (MESP) analysis. The present study shows that the difference between MESP at the nucleus of the para carbon of substituted benzene and a carbon atom in benzene, designated as ΔVC, is very useful to quantify and classify substituent effects. On the basis of positive and negative ΔVC values, a broad classification of around 381 substituents into electron withdrawing and donating categories is made. Each category is again sorted based on the magnitude of ΔVC into subcategories such as very strong, strong, medium, and weak electron donating/withdrawing. Furthermore, the data are used to show the transferability and additivity of substituent effects in π-conjugated organic molecules such as condensed aromatic, olefinic, acetylenic, and heterocyclic systems. The transferability properties hold good for ΔVC in all these molecular systems. The additive properties of substituent effects are strongly reflected on ΔVC and the predictive power of the data to assign the total substituent effects of multi-substituted systems is verified. The ΔVC data and the present classification of substituents are very useful to design π-conjugated organic molecular systems with desired electron rich/poor character.

Synthesis and Characterization of Oxazaborinin Phosphonate for Blue OLED Emitter Applications

“…The classical Phospho‐Fries‐rearrangement involves the conversion of an aryl phosphate to an ortho‐hydroxyarylphosphonate . The transposition of the phosphoryl moiety is initiated by formation of an aryl anion adjacent to the phosphate substituent .…”

“…The electron withdrawing properties of the phosphonate group can make the connected core electron deficient, improving its electron transport properties . HOMO and LUMO are also shifted due to the electron withdrawing character of the P=O bond . The tetrahedral geometry is also beneficial to the amorphous morphology of the organic materials because it is difficult to stack molecules containing P=O regularly.…”

“…[28] HOMO and LUMO are also shifted due to the electron withdrawing character of the P=O bond. [29] The tetrahedral geometry is also beneficial to the amorphous morphology of the organic materials because it is difficult to stack molecules containing P=O regularly. Thus, the introduction of this group into pyridylphenol ligands of boron complexes could make it a favourable technique for property tuning in order to obtain superior blue emitters for OLEDs.…”

Predicting reduction potentials of 1,3,6‐triphenyl fulvenes using molecular electrostatic potential analysis of substituent effects

“…A recent study from our group, quantified the substituent effect in organic molecules based on MESP parameter which is the difference between MESP at the nucleus of the para carbon of substituted benzene and a carbon atom in benzene. Further, using the MESP parameter for a large variety of benzene derivatives, the transferability and additivity properties of substituent effects in conjugated organic molecules were established . Previously, a study conducted on cobalt electrocatalysts proved that the reduction potential ( E 0 ) show a correlation with MESP at cobalt center which enabled a direct prediction of E 0 from the MESP values …”

Electrostatics for probing lone pairs and their interactions

“…Further, MESP analysis opens up new ways to classify, quantify, and characterize various types of lone pairs in chemical systems and provides a simple interpretation of chemical reactivity. MESP analysis has already shown its utility in the study of understanding electron localization/delocalization features and also for interpreting a wide range of chemical and biological phenomena …”