C-C and C-H bond cleavage reactions in acenaphthylene aromatic molecule, an ab-initio density functional theory study European Journal of Chemistry 10 (4) (2019) 403-408 European Journal of Chemistry View Journal Online View Article Online C-C and C-H bond cleavage reactions in acenaphthylene aromatic molecule, an ab-initio density functional theory study Muthana Abduljabbar Shanshal * and Qhatan Adnan Yusuf Department of Chemistry, College of Science, University of Baghdad, Jadirriya, Baghdad, 00964-01, Iraq mshanshal2003@yahoo.com (M.A.S.), drqhatanscience@yahoo.com (Q.A.Y.) * Corresponding author at: Department of Chemistry, College of Science, University of Baghdad, Jadirriya, Baghdad, 00964-01, Iraq. Tel: +964.790.2824400 Fax: +964.790.2824400 e-mail: mshanshal2003@yahoo.com (M.A. Shanshal). 10.5155/eurjchem.10.4.403-408.1889 Received: 07 May 2019 Received in revised form: 22 September 2019 Accepted: 27 September 2019 Published online: 31 December 2019 Printed: 31 December 2019 The ab-initio DFT method (B3LYP) is applied to the study of the C-C and C-H bond cleavage reactions in acenaphthylene molecule. It is found that the C-C bond cleavage proceeds via a singlet aromatic transition state, compelled through a disrotatoric ring opening reaction. A sigmatropic H atom shift follows the transition state in some of these reactions, where the formation of a methylene -CH2, acetylenyl-, allenyl- or butadienyl moiety in the final product is possible. The calculated activation and reaction energies for the C-C ring opening are 164- 236 and 52-193 kcal/mol, respectively. The calculated cleavage reaction energies for the C-H bonds are 117-122 kcal/mol and the activation energies are 147-164 kcal/mol. DFT B3LYP Ab initio Reaction paths Acenaphthylene C-C and C-H bond cleavage Cite this: Eur. J. Chem. 2019, 10(4), 403-408 Journal website: www.eurjchem.com 1. Introduction Due to their industrial importance, the study of the thermal degradations of polycyclic aromatic hydrocarbons (PAH) had been a subject for numerous experimental and theoretical investigations [1-13]. In previous papers, we reported quantum mechanically calculated structures and energies of the transition states (TS) and reaction products (RP) of the C-C and C-H bond cleavage reactions for a number of poly-aromatic hydrocarbon molecules [14-21]. We applied for these treatments the ab-initio Density Functional Theory (DFT) method [23-27]. On the basis of the obtained results, one could conclude the following facts concerning the C-C bond cleavage reactions; (i) Singlet (S) electronically configured transition states (TS) resulted for all the studied reactions. No triplet (T) TS’s seemed probable. The ring opening reaction was of disrotatoric nature, (ii) All the calculated cyclic transition states obeyed the Hückel’s (4n+2) rule for aromaticity. The law of aromatic transition state [28] seemed to be obeyed, (iii) For those C-C bond cleavage reactions, which ended in singlet reaction products, the ring cleavage was accompanied by sigmatropic shifts of a H· atom, which lead to the formation of =CH2 or –CH= moieties on one side and of an acetylenyl-, allenyl- or butadienyl- group on another side of the product molecule. No such shifts were predicted for the triplet reaction products, and (iv) Molecular strain is an effective factor in determining the structure of both the transition states and reaction products. As for the C-H bond cleavage reactions, they seemed to follow a common pattern, i.e. coplanar TS’s and RP’s with common reaction energy values of 116-123 kcal/mol. To achieve a wide generalization for these conclusions, it was necessary to extend the calculations to other members of the PAH family. In the present paper, we report such a study for the bond cleavage reactions of the acenaphthylene PAH molecule (Figure 1). Figure 1. Acenaphthylene molecule. ABSTRACT RESEARCH ARTICLE KEYWORDS European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2019 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.10.4.403-408.1889 http://dx.doi.org/10.5155/eurjchem.10.4.403-408.1889 https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.10.4.403-408.1889&domain=pdf&date_stamp=2019-12-31 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.10.4.403-408.1889 mailto:mshanshal2003@yahoo.com mailto:drqhatanscience@yahoo.com mailto:mshanshal2003@yahoo.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.10.4.403-408.1889&domain=pdf&date_stamp=2019-12-31� 404 Shanshal and Yusuf / European Journal of Chemistry 10 (4) (2019) 403-408 Table 1. Calculated energy values for the C-C and C-H bond cleavage reactions in acenaphylene molecule *. Bond types Transition state Singlet state Triplet state Bond length (Å) Energy (kcal/mol) Bond length (Å) Energy (kcal/mol) Bond length (Å) Energy (kcal/mol) C2a-C3 3.9 192.317 db 4.0 124.471 4.0 154.808 C3-C4 3.9 173.570 sb 4.0 52.230 4.0 117.697 C2a-C8b 3.2 163.963 sb 3.4 139.791 3.4 126.105 C2a-C2 3.8 143.619 sb 3.9 24.540 3.9 105.464 C8b-C5a 3.6 236.251 db 3.7 192.755 4.0 214.682 C5a-C5 3.8 164.241 sb 3.9 120.127 4.1 128.298 C5-C4 4.1 190.447 db 4.3 122.048 4.4 166.601 C1-C2 3.8 212.010 db 3.9 181.186 3.9 178.561 C3-H3 3.6 151.296 - - 3.7 117.220 C2-H2 4.0 164.002 4.1 121.399 4.1 121.681 C4-H4 3.9 156.694 - - 4.0 117.237 C5-H5 4.1 147.169 4.2 117.438 4.2 117.674 * db: Essential double bond, sb: Essential single bond. Bond Length ∆ E( kC al /m ol ) 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 200 250 Figure 2. Potential energy curve for C1-C2 bond cleavage of acenaphthylene molecule showing the activation energy (Ea = 212.010 kcal/mol) and reaction energy for the product, in the triplet state (Er = 178.561 kcal/mol). 2. Experimental The Gaussian 03 program package was operated to obtain all calculations. B3LYP method with the standard 6-311G(d,p) basis set were used for the calculation [28,29]. Restricted energy minimization was applied, such that each value of the reaction coordinate (the bond length) was kept constant whereas total minimization was carried out for the other (3N- 5) internal coordinates. 3. Results and discussion Accurate evaluation of the reaction path is required for the quantitative description of the C-C and C-H bond cleavage [14,15]. For this purpose, we chose the evaluation of the total energy of the reacting molecule as function of the corresponding C-C or C-H bond length, where both singlet and triplet electron configurations are considered. The configuration with the lower energy value was adopted on plotting the reaction path, in which the reaction transition state and final products could be determined graphically, Figure 2. Figure 3 and 4 show the illustrated calculation results for the different C-C bonds in acenaphthylene. As for the C1-C2 bond the reaction proceeds via a singlet transition state towards the triplet reaction product (Figure 3). No H atom shift results for this reaction, a fact which seems common for all triplet product C-C cleavage reactions. Both the reaction transition state and the reaction product exhibit a coplanar conformation. As for the C3-C4 bond cleavage reaction, a coplanar singlet reaction product is formed in which a C5 to C3 H atom shift is obvious (Figure 3). The coplanar reaction product includes a C3H2 group together with a C4(H)C5··· acetenyl group conjugated to the coplanar molecular rings. The C4-C5 bond cleavage proceeds through the singlet transition state towards a coplanar reaction product with a simultaneous H atom shift from C3 to C4 (Figure 4). The transition state conforms to a six carbon atoms ring with 6π electrons. The C2a-C3 bond cleavage proceeds towards a singlet reaction product with a H atom shift from C4 to C3 forming a C3H2 and a C3-C4-C5-allenyl group. The reaction product depicts an out of plane conformation in which the six membered ring is twisted out of the molecular plane (C6H6 group out of the molecular plane), as shown in Figure 3 and 4. The C2a-C8b inner bond cleavage proceeds in a disrotatoric manner, via a singlet transition state, towards a triplet reaction product (Figure 3). No H atom shift results from the calculation. The transition state is reached at a relatively short C…C distance, 3.3 Å, as compared with C…C distances of other bonds, 3.8 to 4.3 Å. Cleavage of the essential single bond C2a-C2 yields a coplanar singlet reaction product with a H atom shift from C1 to C2a. An in-plane C2-C1 acetylenic group is formed, too. The cleavage of C8b-C5a bond conforms to a disrotatoric motion of both C atoms (Figure 4). The singlet transition state exhibits a slight deformation from planarity, whereas the singlet reaction product possess a tub type 12 carbon atom frame, with the C5a-C8b distance 3.7 Å. As for the C5a-C5 essential single bond, the cleavage reaction proceeds through a coplanar transition state towards an allenyl- substituted indane structure. A H atom shift, from C4 atom to C5 proceeds together with the ring opening (Figure 4). Figure 5 includes the calculated structures and energy values for the C-H bond cleavage reactions in acenaphthylene. It is easily seen that all the reactions proceed in a coplanar manner, and that the reaction energy values range from 117 to 122 kcal/mol, Table 1. Table 1 includes the ab-initio DFT calculated energy values for the C-C and C-H bond cleavage in acenaphthylene molecule. 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.4.403-408.1889 Shanshal and Yusuf / European Journal of Chemistry 10 (4) (2019) 403-408 405 E* (kcal/mol) Er (kcal/mol) H-shift 212.010 178.561 Not determined T.S. BL. = 3.8 Å R.P. (T), B.L. = 3.9 Å C1-C2 E* (kcal/mol) Er (kcal/mol) H-shift 143.619 24.540 C1→C2a T.S. BL. = 3.8 Å Singlet R.P., B.L. = 3.9 Å C2-C2a E* (kcal/mol) Er (kcal/mol) H-shift 163.96 126.105 Not determined T.S. BL. = 3.2 Å R.P. (T), B.L. = 3.3 Å C2a-C8b E* (kcal/mol) Er (kcal/mol) H-shift 173.570 52.230 C5→c3 T.S. BL. = 3.9 Å R.P., B.L. = 4.0 Å C3-C4 Figure 3. Calculated illustration figures and energy values for the different C-C bond cleavage reactions of acenaphthylene molecule. 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.4.403-408.1889 406 Shanshal and Yusuf / European Journal of Chemistry 10 (4) (2019) 403-408 E* (kcal/mol) Er (kcal/mol) H-shift 190.447 122.048 C3 → C4 T.S. BL. = 4.1 Å R.P. (S), B.L. = 4.2 Å C4-C5 E* (kcal/mol) Er (kcal/mol) H-shift 192.317 124.471 C4 → C3 T.S. BL. = 3.9 Å R.P., B.L. = 4.0 Å C2a-C3 E* (kcal/mol) Er (kcal/mol) H-shift 236.251 192.755 Not determined T.S. BL. = 3.6 Å R.P. (S), B.L. = 3.7 Å C8b-C5a E* (kcal/mol) Er (kcal/mol) H-shift 164.241 120.127 C4 → C5 T.S. BL. = 3.8 Å R.P. (S) B.L. = 3.9 Å C5a-C5 Figure 4. Calculated illustration figures and energy values for the different C-C bond cleavage reactions of acenaphthylene molecule. 4. Conclusion The obtained results in this manuscript indicate the following results; i. they confirm our former findings that all the C- C bond cleavage reactions proceed via disrotatoric ring opening passing through singlet transition states, ii. for reactions ending with singlet products a H shift occurs provided that the formation of conjugated acetenyl-, butadienyl- or allenylyl- side chain is possible, such as for the C3-C4, C4-C5, C2a-C3, C2a-C2, and C5a-C5 bonds. No such shift result for the triplet state product reactions, iii. The calculated reaction activation energies range from 192.32 to 236.25 kcal/mol for the C-C essential double bonds (db) and from 143.62 to 173.65 kcal/mol for the C-C essential single bonds 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.4.403-408.1889 Shanshal and Yusuf / European Journal of Chemistry 10 (4) (2019) 403-408 407 E* (kcal/mol) Er (kcal/mol) 164.002 121.681 (a) T.S. BL. = 4.0 Å R.P. (T) B.L. = 4.1 Å E* (kcal/mol) Er (kcal/mol) 151.296 117.220 (b) T.S. BL. = 3.6 Å R.P. (T), B.L. = 3.7 Å E* (kcal/mol) Er (kcal/mol) 156.694 117.237 (c) T.S. BL. = 3.9 Å R.P. (T) B.L. = 4.0 Å E* (kcal/mol) Er (kcal/mol) 147.169 117.438 (d) T.S. BL. = 4.1 Å R.P. (T), B.L. = 4.2 Å Figure 5. Calculated figures for the different C-H bond cleavage reactions of acenaphthylene molecule, (a) C2-H2, (b) C3-H3, (c) C4-H4, (d) C5-H5. (sb), and iv. All C-H bond cleavage reactions proceed in a coplanar manner, the corresponding activation energies range from 147.17 to 164.00 kcal/mol and the reaction energies from 117.44 to 121.40 kcal/mol. Acknowledgements This article includes a part of the PhD thesis of Qhatan Adnan Yusuf with Muthana Abduljabbar Shanshal supervision, College of Science, University of Baghdad, Baghdad, Iraq. 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.4.403-408.1889 408 Shanshal and Yusuf / European Journal of Chemistry 10 (4) (2019) 403-408 Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Muthana Abduljabbar Shanshal http://orcid.org/0000-0001-6721-4001 Qhatan Adnan Yusof http://orcid.org/0000-0002-7053-3254 References [1]. Ren, R. L.; Itoh, H.; Ouchi, K. Fuel 1989, 68, 58-65. [2]. Ninomiza, Y. D.; Suzuki, Z. Y. Fuel 2000, 79, 449-457. [3]. Guerrin, M. 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G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.; Gaussian03, Gaussian Inc. Pittsburgh, PA, 2003. Copyright © 2019 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.4.403-408.1889 http://orcid.org/0000-0001-6721-4001 http://orcid.org/0000-0002-7053-3254 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 3. Results and discussion 4. Conclusion Acknowledgements Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: