Cycloaddition reaction of methylidyne radical with dipyrromethanol: quantum chemical insights into the formation of di(pyridin-2-yl)methanol

Abstract

Density functional theory was employed to investigate methylidyne radical reaction on to the unsaturation of dipyrromethanol moiety through cycloaddition forming a six membered di(pyridin-2-yl)methanol followed by H-elimination via ring expansion. Time-dependent density functional theory (TD-DFT) simulations were performed to figure out the ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol. Ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that two sharp absorption peaks were obtained at λ_max = 161 nm and 206 nm for the reactant dipyrromethanol while a sharp peak was observed for the product di(pyridin-2-yl)methanol at shorter wavelength (λ_max = 170 nm). The theoretical IR spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that a significant red shift of 129 cm⁻¹ was observed in the case of di(pyridin-2-yl)methanol due to presence of two strong intra-molecular hydrogen bonds, which indicates its higher stability than the dipyrromethanol. HOMO–LUMO energy gap calculations and natural bond orbital (NBO) analysis endorse the type of electronic transition for the desired product di(pyridin-2-yl)methanol is π–π*. The global reactivity analysis shows the electron donor and acceptor nature of dipyrromethanol and methylidyne radical, respectively. A potential energy surface is constructed via methylidyne radical addition, ring expansion, and hydrogen elimination transition states. Thermodynamics study and potential energy surface of the title reaction indicates its highly exothermicity and spontaneous in nature.

Graphical Abstract

Keywords:

• HOMO–LUMO
• NBOs
• potential energy surface
• quantum chemical calculation
• the global reactivity descriptors

Acknowledgments

SP gives thanks to the Department of Chemistry, DIT University for providing computer resources and a teaching assistantship.

Disclosure statement

No potential conflict of interest was stated by the author(s).

Author contributions

SP performed all the computations for the electronic structure. SP and MRD prepared the original draft of the manuscript.

Data availability statement

All data obtained through this computation are tabulated in Supporting Information.

Additional information

Funding

MRD thanks the Department of Chemistry, DIT University for supporting this work through the seed funding grant by the Dean Research & consultancy of DIT University, Dehradun, India [Project No. DITU/R & D/2022/015/Chemistry].