The quadrapolar character of the Markovnikov reaction transition state

• Calculation of the Markovnikov transition state for H2O and HX (X = F, Cl, Br).
• Validation of transition state using intrinsic reaction coordinate and vibrational frequency.
• Quantitative agreement of transition state energy based on partition function.
• Dipolar nature of transition state validated using Hirshfeld charge and Fukui function.
• Explanation of Markovnikov regioselectivity for H2O based on dipolar transition state.

The properties of the transition states for the electrophilic addition reactions of four molecules of the type HX (X = Br, Cl, F and OH) to 1-propene form 2-X propane by the Markovnikov mechanism have been calculated using density functional theory (DFT). A comparative study of the transition state along the reaction path for both M and AM addition was studied in order to understand the origins of regioselectivity of H2O. The quadrapolar nature of the transition state is arises because of a sequential mechanism, in which the addition across the π-bond occurs in two steps, first H+ and then X−. The M reaction mechanism is consistent with a H+X− dipole which induces an oppositely polarized C1−C2+ dipole in the transition state, resulting in a quadrupole. The C1−C2+ dipole in the M mechanism is consistently larger than the C1+C2− dipole of the AM transition state for all species studied.

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