Revisiting Markovnikov addition to alkenes via molecular electrostatic potential

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Physical Chemistry

Background:

• Understanding substituent effects on molecular reactivity is crucial in organic chemistry.
• Molecular electrostatic potentials (MESP) provide insights into charge distribution and reactivity.
• Ethylene derivatives are fundamental building blocks in organic synthesis.

Purpose of the Study:

• To characterize the MESP in the pi-region of substituted ethylenes (CH(2)CHR).
• To classify substituents as electron donating or withdrawing based on MESP.
• To correlate MESP with the electronic effects and reactivity in HCl addition reactions.

Main Methods:

• Calculation of Molecular Electrostatic Potentials (MESP) for substituted ethylenes.
• Identification of the minimum MESP value (V(min)) in the pi-region.
• Correlation analysis with Hammett sigma(p) constants.

Main Results:

• Substituents were classified as electron donating or withdrawing based on V(min) changes.
• V(min) values showed a linear correlation with Hammett sigma(p) constants.
• Electron-donating groups shifted V(min) closer to the unsubstituted carbon, favoring regiospecific pi-complex formation and Markovnikov addition of HCl.
• Electron-withdrawing groups resulted in equidistant V(min) locations and less regiospecific interactions.

Conclusions:

• Substituent electronic effects in substituted ethylenes are similar to those in substituted benzenes.
• MESP analysis effectively predicts the regioselectivity of HCl addition to substituted ethylenes.
• The interaction energy of pi-complex formation correlates with MESP values.