DFT Study on the Photoisomerization of Carvone: Difference between revisions

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==Declarations==
==Declarations==
=== Conflict of Interest ===
=== Conflict of Interest ===
The opinions expressed in this contribution are personal and do not in any way commit to the Ministry of Foreign Affairs and International Cooperation.
The Authors declare that there is no conflict of interest.
The Authors declare that there is no conflict of interest.


Latest revision as of 08:28, 24 January 2026

Published
January 24, 2026
Title
DFT Study on the Photoisomerization of Carvone
Authors
Lucia Emanuele, Rocco Racioppi and Maurizio D’Auria
DOI
10.62684/UHJS3297
Keywords
carvone; terpenes; photoisomerization; DFT calculation; CASSCF.
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Lucia Emanuele (a), Rocco Racioppi (b), Maurizio D’Auria (b)

(a) Department of Arts and Restoration, University of Dubrovnik, Branitelja Dubrovnika 41, 20000 Du-brovnik, Croatia; lemanuel@unidu.hr

(b) Dipartimento di Scienze di Base ed Applicate, Università della Basilicata, V.le dell’Ateneo Lucano 10, 85100 Potenza, Italy; rocco.racioppi@unibas.it; maurizio.dauria53@gmail.com


Correspondence to: Maurizio D’Auria, maurizio.dauria53@gmail.com

Abstract

A theoretical investigation of the photochemical isomerization of carvone was conducted using Density Functional Theory (DFT) and multiconfigurational methods. Geometry optimizations, excited-state calculations, and reaction pathway analyses were performed at the B3LYP/6-311G+(d,p) level, supported by TD-DFT and CASSCF(6,6) calculations. The results provide strong computational evidence for the mechanism proposed by Büchi in 1957, in which the reaction proceeds through the first excited triplet state rather than a concerted singlet-state cycloaddition. After photoexcitation, intersystem crossing leads to a triplet state with pronounced radical character at the carbon atom β to the carbonyl group. Intramolecular coupling with the terminal olefinic carbon of the isopropenyl side chain generates a triplet biradical intermediate through a very low activation barrier (0.22 eV), which subsequently cyclizes to form the observed tricyclic terpene. Although the final product is thermodynamically less stable than the reactant, the process is kinetically feasible under photochemical conditions. CASSCF calculations did not reveal a conical intersection in the first excited singlet state, excluding a concerted [2+2] pathway. Solvent effects were also rationalized, with polar, hydrogen-bonding solvents significantly stabilizing the biradical intermediate, in agreement with experimentally observed variations in quantum yield.

Declarations

Conflict of Interest

The Authors declare that there is no conflict of interest.

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