Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2018 Aug 1;3(8):8546–8552. doi: 10.1021/acsomega.8b01003

Computational Study on Ring Saturation of 2-Hydroxybenzaldehyde Using Density Functional Theory

Anand Mohan Verma 1, Kushagra Agrawal 1, Nanda Kishore 1,*
PMCID: PMC6644427  PMID: 31458984

Abstract

graphic file with name ao-2018-01003c_0004.jpg

Bio-oil produced from pyrolysis of lignocellulosic biomass consists of several hundreds of oxygenated compounds resulting in a very low quality with poor characteristics of low stability, low pH, low stability, low heating value, high viscosity, and so on. Therefore, to use bio-oil as fuel for vehicles, it needs to be upgraded using a promising channel. On the other hand, raw bio-oil can also be a good source of many specialty chemicals, e.g., 5-HMF, levulinic acid, cyclohexanone, phenol, etc. In this study, 2-hydroxybenzaldehyde, a bio-oil component that represents the phenolic fraction of bio-oil, is considered as a model compound and its ring saturation is carried out to produce cyclohexane and cyclohexanone along with various other intermediate products using density functional theory. The geometry optimization, vibrational frequency, and intrinsic reaction coordinate calculations are carried out at the B3LYP/6-311+g(d,p) level of theory. Furthermore, a single point energy calculation is performed at each structure at the M06-2X/6-311+g(3df,2p)//B3LYP/6-311+g(d,p) level of theory to accurately predict the energy requirements. According to bond dissociation energy calculations, the dehydrogenation of formyl group of 2-hydroxybenzaldehyde is the least energy demanding bond cleavage. The production of cyclohexane has a lower energy of activation than the production of cyclohexanone.

1. Introduction

Due to declining fossil fuels and increasing pollution, there is a strong necessity to find an alternative and clean energy resource that can aid the present energy demands and reduce the pollution level. Currently, renewable energy resources, e.g., tidal energy, solar energy, biomass, wind energy, geothermal energy, and so on, are being largely utilized. They are providing a good relief for the present energy demand; however, their proper utilization still needs to be explored. Nevertheless, out of all renewable energy resources, only biomass has the ability to deliver sustainable carbon element.1−4 The sustainability of carbon element is necessary to achieve the production of transportation fuels or specialty chemicals.5 The lignocellulosic biomass is cheap, abundant, and easily available in most countries; therefore, the research based on lignocellulosic biomass conversion into biofuel has enormously increased in the last few decades.2 The lignocellulosic biomass basically contains three fractions, viz., lignin, hemicellulose, and cellulose.1,6 The research based on the cellulose and hemicellulose fractions of lignocellulosic biomass has received considerable attention in the past few years, but the lignin fraction has been ignored constantly because of its complex structure, although it has a high energy density compared to other two fractions.7 Nevertheless, there are various channels to convert the lignocellulosic biomass into bio-oil, e.g., pyrolysis, liquefaction, hydrolysis, and gasification, and the pyrolysis process has been reviewed to be the most economical and advantageous.3,8 However, the bio-oil produced from pyrolysis of lignocellulosic biomass comprises several hundreds of oxygenated compounds that lower its quality, endowing it with low heating value, low pH, low stability, low stability, high viscosity, and so on.4 Therefore, it needs to be upgraded to serve as a fuel for vehicles. Furthermore, unprocessed bio-oil is a great source of many specialty or platform chemicals, such as hydroxymethyl furfural, furfural, levulinic acid, dimethyl furan, and so on.1,5

As it has been pointed out that cellulose and hemicellulose fractions have received much attention compared to the lignin fraction, in this study, 2-hydroxybenzaldehyde, a component of phenolic fraction derived from lignin, has been selected as the bio-oil model compound. In the past, a few phenolic components, such as guaiacol,9−15 catechol,9,16 phenol,10,14,16,17 vanillin,18,19 anisole,14 and so on, have been studied both experimentally and numerically. This component has been recently considered by Verma and Kishore20 for its decomposition into benzene as the end product; however, there has been no further study regarding its ring saturation, which is more likely to occur in the presence of high hydrogen pressure-based hydrodeoxygenation conditions. Although a few authors21−24 have carried out pyrolysis of a few bio-oil model compounds and observed 2-hydroxybenzaldehyde as one of the products in the pyrolysis product mixtures, further experiments for upgrading 2-HB have not been carried out to date. For instance, Robichoud et al.21 carried out a pyrolysis study on dimethoxybenzene model compound and observed 2-hydroxybenzaldehyde as one of the products. Similarly, Zhang et al.24 also carried out pyrolysis study on the lignin dimer model compound and reported 2-hydroxybenzaldehyde as one of the products along with guaiacol, catechol, and others. Since 2-hydroxybenzaldehyde comprises two oxy-functionals, namely, hydroxyl and aldehyde groups, it still needs to be upgraded to achieve the nonoxygenated component. Therefore, 2-hydroxybenzaldehyde is selected as the bio-oil model compound and its conversion to lower fractions has been numerically attempted here.

In this numerical study, 2-hydroxybenzaldehyde is allowed to undergo two reaction pathways producing cyclohexane and cyclohexanone, respectively. These reaction schemes are depicted in Figure 1. The notations in Figure 1 are labeled as X_Y, where X denotes the reaction pathway number and Y denotes the structure under that reaction pathway. Similarly, transition-state structures in the potential energy surfaces (PESs) are denoted as TSX_Y, where X is the reaction pathway number and Y denotes the transition-state number.

Figure 1.

Figure 1

Open in a new tab

Reaction schemes for the conversion of 2-hydroxybenzaldehyde.

In Figure 1, it can be seen that the reaction pathway 1 produces cyclohexane. The preparatory part of reaction pathway 1 is the hydrogenation of carbon atom (para-positioned to OH group), followed by ring saturation of 2-hydroxybenzaldehyde using five further atomic hydrogenation reactions. The produced component 1_f after the ring saturation undergoes hydroxyl cleavage, followed by a single-step hydrogenation reaction to produce 1_h. Finally, structure 1_h follows two pathways. Under primary reaction pathway 1, the formyl group is cleaved, followed by a single-step hydrogenation reaction to produce cyclohexane, and under secondary reaction pathway 1, i.e., 1a, structure 1_h undergoes decarbonylation reaction to produce cyclohexane. On the other hand, reaction pathway 2 starts from the dihedral change of hydrogen atom of the hydroxyl group to initiate the keto–enol tautomerization reaction. The keto–enol tautomerization reaction of structure 2_a produces 2_b, which further undergoes ring saturation to produce structure 2_f. Finally, structure 2_f undergoes the decarbonylation reaction to produce cyclohexanone. All reaction steps of each reaction pathway are considered theoretically at the B3LYP/6-311+g(d,p) level of the theory under density functional theory (DFT) framework. The single point energy (SPE) calculation is performed for each structure at the M06-2X/6-311+g(3df,2p)//B3LYP/6-311+g(d,p) level of theory to predict energies accurately.

2. Results and Discussion

2.1. Bond Dissociation Energy (BDE)

A thorough analysis of bond dissociation energy (BDE) of 2-hydroxybenzaldehyde with all possible bond cleavages was reported in our previous work.20 It has been reported that bond dissociation energies of 2-hydroxybenzaldehyde are quite high, i.e., in the range of 92–115 kcal/mol. The least energy demanding bond cleavage, i.e., D3 (dehydrogenation of the formyl group), requires 92.22 kcal/mol.20 Along with the most favorable bond dissociation site D3, dehydrogenation of the hydroxyl group (D2) was reported as the second most favorable bond cleavage site.20 It is also clear that dehydrogenation of phenyl ring of 2-HB is not favorable at all because the energy demand due to each hydrogen bond cleavage from phenyl ring of 2-HB is in the range of 112–115 kcal/mol.20 Therefore, cleavage of hydrogen atoms from phenyl ring is not advisable. In such scenario of high bond dissociation energies due to scissions of atoms/functionals of 2-HB, it is highly probable that the ring saturation of 2-HB may lead to a low energy demanding reaction pathway, which is the aim of this work. There are two ways of saturating the aromatic ring of 2-HB, i.e., first by direct ring hydrogenation and second by keto–enol tautomerization followed by ring hydrogenation.

2.2. Reaction Pathway 1

Reaction pathway 1 is about the direct ring hydrogenation reaction. The potential energy surfaces (PESs) of reaction pathways 1 and 1a are shown in Figure 2, and the corresponding optimized molecular structures are shown in Figure 3. Interatomic bond distances in the transition-state structures of Figure 3 are shown in angstrom (Å) units. The Cartesian coordinates of a few optimized molecular structures are given in the Supporting Information.

Figure 2.

Figure 2

Open in a new tab

Potential energy surfaces of reaction pathways 1 and 1a.

Figure 3.

Figure 3

Open in a new tab

Optimized molecular structures of reaction pathways 1 and 1a.

The reaction pathway 1 starts with a single-step hydrogenation reaction at the fifth carbon position of the aromatic ring of the 2-hydroxybenzaldehyde structure (see structure 1_a in Figure 1), followed by another atomic hydrogenation reaction to saturate the generated radical by the first hydrogenation reaction. The first hydrogenation reaction requires 4.62 kcal/mol of activation barrier (see TS1_1 in Figures 3 and 4) according to single point energetics at the M06-2X/6-311+g(3df,2p)//B3LYP/6-311+g(d,p) level of theory.

Figure 4.

Figure 4

Open in a new tab

Potential energy surface of reaction pathway 2.

As it is known that bond dissociation and radical recombination reactions do not possess any transition-state structure, the energy release during the recombination reaction of structure 1_a and H radicals is calculated by BDE approximation. According to BDE at the B3LYP/6-311+g(d,p) level of theory, the recombination of radicals 1_a and H to produce structure 1_b releases 73.58 kcal/mol of energy. Further, another transition-state structure is located for the hydrogenation reaction of structure 1_b to produce 1_c at potential energy surface (PES) as TS1_2 that requires only 2.89 kcal/mol of energy to surpass the barrier height. This follows through another radical recombination reaction of structure 1_c and H that releases 82.60 kcal/mol of energy. Similar to the reaction steps 2-HB → 1_a → 1_b, further hydrogenation reactions of structure 1_d are carried out as 1_d → 1_e → 1_f, where the activation barrier of 1_d → 1_e and energy release during 1_e → 1_f are calculated as 4.30 and 81.99 kcal/mol, respectively. The produced component after the aromatic ring saturation of 2-HB is identified as 2-hydroxycyclohexane-1-carbaldehyde. Further, the cleavage of hydroxyl group of structure 1_f is carried out with a calculated BDE of 86.57 kcal/mol, followed by a radical recombination reaction of structure 1_g and a hydrogen radical with an energy release of 94.49 kcal/mol. Afterward, the produced component, i.e., cyclohexanecarbaldehyde (structure 1_h), follows two pathways. The first pathway proceeds as the primary reaction pathway 1 (bold black arrows in Figure 1), which cleaves the formyl group from structure 1_h with a BDE of 71.43 kcal/mol, followed by saturation of generated radical with a hydrogen radical releasing 94.19 kcal/mol of energy to produce cyclohexane. On the other hand, the secondary reaction pathway 1 (nonbold black arrows in Figure 1) involves a decarbonylation reaction to directly produce cyclohexane. The barrier height of the decarbonylation is calculated to be 87.31 kcal/mol.

In Figure 3, it can be seen that the highest uphill is due to the very first hydrogenation reaction of 2-HB, which is 4.62 kcal/mol at the potential energy surface, and other stationary states are in the negative side. Figure 3 clearly suggests an overall activation energy of only 4.62 kcal/mol of energy, which is a very favorable environment for this system even at lower temperature and pressure conditions. Also, it can be seen that the decarbonylation reaction of structure 1_h is slightly favorable for the direct cleavage of the formyl group followed by hydrogenation reaction.

2.3. Reaction Pathway 2

Reaction pathway 2 is about the production of cyclohexanone. The potential energy surface is shown in Figure 4 by a blue smooth line, and the corresponding molecular structures are shown in Figure 5.

Figure 5.

Figure 5

Open in a new tab

Optimized molecular structures of reaction pathway 2.

Reaction pathway 2 starts with the dihedral change of hydrogen atom of the hydroxyl group. It can be seen from the potential energy surface of reaction pathway 2 (Figure 4) that 2-HB is the ground-state structure and 10.57 kcal/mol more stable than structure 2_a (energetically less stable configuration of 2-HB). The dihedral change of hydrogen atom occurs with a barrier height of 13.80 kcal/mol, and this reaction step is essential for further initiation of the keto–enol tautomerization reaction. The keto–enol tautomerization reaction step (2_a → 2_b), i.e., migration of hydrogen atom from hydroxyl group to the ortho-positioned carbon atom, produces 6-oxocyclohexa-1,3-diene-1-carbaldehyde with a barrier height of 73.90 kcal/mol. Further, a single-step hydrogenation reaction at structure 2_b is carried out with a barrier height of only 1.36 kcal/mol, followed by combination reaction of a hydrogen radical and structure 2_c releasing 77.53 kcal/mol of energy. Further, similar to the reaction steps 2_b → 2_c → 2_d, the reaction steps 2_d → 2_e → 2_f are performed with a barrier height of 1.75 kcal/mol for reaction step 2_d → 2_e and an energy release of 83.62 kcal/mol for reaction step 2_e → 2_f.

The produced compound after the conversion of double bonds between carbon atoms into single bonds is recognized as 2-oxocyclohexane-1-carbaldehyde. Finally, to produce cyclohexanone from 2-oxocyclohexane-1-carbaldehyde, a decarbonylation reaction is carried out, which occurs with a barrier height of 71.04 kcal/mol.

The production of cyclohexanone from 2-hydroxybenzaldehyde witnesses many reaction steps. It can be seen in Figure 4 that the energy state of TS2_2 is highest in the potential energy surface of reaction pathway 2; therefore, this particular energy state will be responsible for the overall activation energy. Therefore, the overall activation energy of reaction pathway 2 is 84.47 kcal/mol, which is very high to achieve at mild reaction conditions. Also, if compared, the production of cyclohexanone requires a considerably larger overall activation barrier (84.47 kcal/mol) than the overall activation barrier in the production of cyclohexane (4.62 kcal/mol). Therefore, it is clear that the possibility of production of cyclohexane from 2-HB will be considerably higher compared to the production of cyclohexanone.

3. Conclusions

In this study, 2-hydroxybenzaldehyde (2-HB), a bio-oil oxygenated component that represents the phenolic fraction of bio-oil, is taken as the bio-oil model compound and its ring saturation is carried out to produce cyclohexane and cyclohexanone. The bond dissociation energy calculations of 2-hydroxybenzaldehyde do not suggest the cleavage of hydrogen atoms from either the phenyl ring or functional groups because of high energy requirements. Therefore, the conversion of 2-HB by ring saturation is carried out to produce cycloproducts. It is observed that the production of cyclohexane is highly favorable compared to the production of cyclohexanone because the overall activation energy of the former is only 4.62 kcal/mol, whereas the latter demanded 84.47 kcal/mol of overall activation energy. In other words, keto–enol tautomerization followed by ring hydrogenation process of 2-HB in gas phase is not preferred compared to direct ring hydrogenation process of 2-HB.

4. Computational Details

The application of density functional theory (DFT) as a computational tool has enormously increased in the recent past due to its reliability and accuracy. Although there are various functionals under DFT, such as LSDA, B3LYP, BLYP, M05, M06-2X, etc., there has been much debate among researchers regarding their accuracy.25 Recently, a few research groups26,27 carried out an extensive survey of DFT functionals applied to various chemical systems. For instance, Goerigk et al.26 performed an extensive review to assess numerous DFT functionals and observed ωB97X-V functional as one of the best functionals among GGA, meta-GGA, and hybrid-GGA functionals. They reported an average performance of B3LYP functional compared to other DFT functionals. Furthermore, Mardirossian and Head-Gordon27 also performed an extensive assessment of numerous DFT functionals and reported root-mean-square deviation (RMSD) values for different data types. They reported ωB97M-V as the best functional because of low RMSD values for barrier heights (1.68) and thermochemistry (2.48) data types. However, an interesting observation in their study is that B3LYP functional performed excellently compared to many well-known DFT functionals, such as PBE, PBE-D3, TPSS-D3, M06-L, and so on. In addition, recently, Simón and Goodman28 have shown that the use of B3LYP functional is a better choice for organic covalent bond-forming reactions; therefore, all geometries and transition-state structures in this study are optimized using B3LYP29,30 functional under DFT31,32 framework. The basis set has been selected as 6-311+g(d,p).33 Normal-mode vibrational frequency calculations are carried out for all optimized structures to test the true natures of optimized structures. One and zero imaginary frequencies in the vibrational frequency result confirm the structure as first-order saddle point and minimum structure on potential energy surface (PES). Furthermore, an intrinsic reaction coordinate34 calculation is also carried out at each true transition-state structure to evaluate the minimum energy path. The single point energy (SPE) calculation is performed for each structure at the M06-2X/6-311+g(3df,2p)//B3LYP/6-311+g(d,p) level of theory to predict energies accurately.

Bond dissociation energy calculations are performed for organic homolysis and radical recombination reactions because of the nonavailability of transition-state structures for such reactions. BDE provides a good approximation for the energy requirement to cleave a chemical bond. The expression of BDE is as follows

4. 1

where H298 is the enthalpy. “A–B” is the molecule with considered cleavage site, A and B are the radicals after bond cleavage of “A–B”.

All quantum chemical calculations are performed in the gas-phase environment using Gaussian 0935 software package with the help of a Gauss View 536 visualizer.

Acknowledgments

The authors acknowledge the financial support (sanction no. 34/20/17/2016-BRNS) from Board of Research in Nuclear Sciences (India) for this work.

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b01003.

  • Cartesian coordinates of a few molecular structures, i.e., structures 2-HB, 1_b, 1_d, 1_f, and 1_j involved in this study are provided in this Supporing Information (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao8b01003_si_001.pdf (614.8KB, pdf)

References

  1. Huber G. W.; Sara I.; Corma A. Synthesis of Transportation Fuels from Biomass. Chem Rev. 2006, 106, 4044–4098. [DOI] [PubMed] [Google Scholar]
  2. Alonso D. M.; Bond J. Q.; Dumesic J. A. Catalytic Conversion of Biomass to Biofuels. Green Chem. 2010, 12, 1493–1513. 10.1039/c004654j. [DOI] [Google Scholar]
  3. Gollakota A. R. K.; Reddy M.; Subramanyam M. D.; Kishore N. A Review on the Upgradation Techniques of Pyrolysis Oil. Renewable Sustainable Energy Rev. 2016, 58, 1543–1568. 10.1016/j.rser.2015.12.180. [DOI] [Google Scholar]
  4. Wang H.; Male J.; Wang Y. Recent Advances in Hydrotreating of Pyrolysis Bio-Oil and Its Oxygen-Containing Model Compounds. ACS Catal. 2013, 3, 1047–1070. 10.1021/cs400069z. [DOI] [Google Scholar]
  5. Huber G. W.; Chheda J. N.; Barrett C. J.; Dumesic J. A. Production of Liquid Alkanes by Aqueous-Phase Processing of Biomass-Derived Carbohydrates. Science 2005, 308, 1446–1450. 10.1126/science.1111166. [DOI] [PubMed] [Google Scholar]
  6. Klass D. L. Biomass for Renewable Energy and Fuels. Encycl. Energy 2004, 1, 193–212. 10.1016/b0-12-176480-x/00353-3. [DOI] [Google Scholar]
  7. Saidi M.; Samimi F.; Karimipourfard D.; Nimmanwudipong T.; Gates B. C.; Rahimpour M. R. Upgrading of Lignin-Derived Bio-Oils by Catalytic Hydrodeoxygenation. Energy Environ. Sci. 2014, 7, 103–129. 10.1039/C3EE43081B. [DOI] [Google Scholar]
  8. Gollakota A. R. K.; Subramanyam M. D.; Kishore N.; Gu S. CFD Simulations on the Effect of Catalysts on the Hydrodeoxygenation of Bio-Oil. RSC Adv. 2015, 5, 41855–41866. 10.1039/C5RA02626A. [DOI] [Google Scholar]
  9. Lee K.; Gu G. H.; Mullen C.; Boateng A.; Vlachos D. G. Guaiacol Hydrodeoxygenation Mechanism on Pt(111): Insights from Density Functional Theory and Linear Free Energy Relations. ChemSusChem 2015, 8, 315–322. 10.1002/cssc.201402940. [DOI] [PubMed] [Google Scholar]
  10. Lu J.; Behtash S.; Mamun O.; Heyden A. Theoretical Investigation of the Reaction Mechanism of the Guaiacol Hydrogenation over a Pt(111) Catalyst. ACS Catal. 2015, 5, 2423–2435. 10.1021/cs5016244. [DOI] [Google Scholar]
  11. Liu C.; Zhang Y.; Huang X. Study of Guaiacol Pyrolysis Mechanism Based on Density Function Theory. Fuel Process. Technol. 2014, 123, 159–165. 10.1016/j.fuproc.2014.01.002. [DOI] [Google Scholar]
  12. Huang J.; Li X.; Wu D.; Tong H.; Li W. Theoretical Studies on Pyrolysis Mechanism of Guaiacol as Lignin Model Compound. J. Renewable Sustainable Energy 2013, 5, 043112 10.1063/1.4816497. [DOI] [Google Scholar]
  13. Bykova M. V.; Bulavchenko O.; Ermakov D. Y.; Lebedev M. Y.; Yakovlev V.; Parmon V. N. Guaiacol Hydrodeoxygenation in the Presence of Ni-Containing Catalysts. Catal. Ind. 2011, 3, 15–22. 10.1134/S2070050411010028. [DOI] [Google Scholar]
  14. Bykova M. V.; Zavarukhin S. G.; Trusov L. I.; Yakovlev V. A. Guaiacol Hydrodeoxygenation Kinetics with Catalyst Deactivation Taken into Consideration. Kinet. Catal. 2013, 54, 40–48. 10.1134/S0023158413010023. [DOI] [Google Scholar]
  15. Verma A. M.; Kishore N. DFT Study on Gas-Phase Hydrodeoxygenation of Guaiacol by Various Reaction Schemes. Mol. Simul. 2017, 43, 141–153. 10.1080/08927022.2016.1239825. [DOI] [Google Scholar]
  16. Lu J.; Heyden A. Theoretical Investigation of the Reaction Mechanism of the Hydrodeoxygenation of Guaiacol over a Ru (0001 ) Model Surface. J. Catal. 2015, 321, 39–50. 10.1016/j.jcat.2014.11.003. [DOI] [Google Scholar]
  17. Bykova M. V.; Ermakov D. Y.; Kaichev V. V.; Bulavchenko O. A.; Saraev A. A.; Lebedev M. Y.; Yakovlev V. Ni-Based Sol-Gel Catalysts as Promising Systems for Crude Bio-Oil Upgrading: Guaiacol Hydrodeoxygenation Study. Appl. Catal., B 2012, 113–114, 296–307. 10.1016/j.apcatb.2011.11.051. [DOI] [Google Scholar]
  18. Wang M.; Liu C.; Xu X.; Li Q. Theoretical Study of the Pyrolysis of Vanillin as a Model of Secondary Lignin Pyrolysis. Chem. Phys. Lett. 2016, 654, 41–45. 10.1016/j.cplett.2016.03.058. [DOI] [Google Scholar]
  19. Liu C.; Deng Y.; Wu S.; Mou H.; Liang J.; Lei M. Study on the Pyrolysis Mechanism of Three Guaiacyl-Type Lignin Monomeric Model Compounds. J. Anal. Appl. Pyrolysis 2016, 118, 123–129. 10.1016/j.jaap.2016.01.007. [DOI] [Google Scholar]
  20. Verma A. M.; Kishore N. Production of Benzene from 2-Hydroxybenzaldehyde by Various Reaction Paths Using IRC Calculations within a DFT Framework. ChemistrySelect 2017, 2, 1556–1564. 10.1002/slct.201601633. [DOI] [Google Scholar]
  21. Robichaud D. J.; Scheer A. M.; Mukarakate C.; Ormond T. K.; Buckingham G. T.; Ellison G. B.; Nimlos M. R. Unimolecular Thermal Decomposition of Dimethoxybenzenes. J. Chem. Phys. 2014, 140, 234302–234314. 10.1063/1.4879615. [DOI] [PubMed] [Google Scholar]
  22. Custodis V. B. F.; Hemberger P.; Ma Z.; Van Bokhoven J. A. Mechanism of Fast Pyrolysis of Lignin: Studying Model Compounds. J. Phys. Chem. B 2014, 118, 8524–8531. 10.1021/jp5036579. [DOI] [PubMed] [Google Scholar]
  23. Huang J.; He C. Pyrolysis Mechanism of α-O-4 Linkage Lignin Dimer: A Theoretical Study. J. Anal. Appl. Pyrolysis 2015, 113, 655–664. 10.1016/j.jaap.2015.04.012. [DOI] [Google Scholar]
  24. Zhang J. J.; Jiang X. Y.; Ye X. N.; Chen L.; Lu Q.; Wang X. H.; Dong C. Q. Pyrolysis Mechanism of a β-O-4 Type Lignin Dimer Model Compound: A Joint Theoretical and Experimental Study. J. Therm. Anal. Calorim. 2016, 123, 501–510. 10.1007/s10973-015-4944-y. [DOI] [Google Scholar]
  25. Zhang I. Y.; Wu J.; Xu X. Extending the Reliability and Applicability of B3LYP. Chem. Commun. 2010, 46, 3057–3070. 10.1039/c000677g. [DOI] [PubMed] [Google Scholar]
  26. Goerigk L.; Hansen A.; Bauer C. A.; Ehrlich S.; Najibi A.; Grimme S. A Look at the Density Functional Theory Zoo with the Advanced GMTKN55 Database for General Main Group Thermochemistry, Kinetics and Noncovalent Interactions. Phys. Chem. Chem. Phys. 2017, 19, 32184–32215. 10.1039/C7CP04913G. [DOI] [PubMed] [Google Scholar]
  27. Mardirossian N.; Head-Gordon M. How Accurate Are the Minnesota Density Functionals for Noncovalent Interactions, Isomerization Energies, Thermochemistry, and Barrier Heights Involving Molecules Composed of Main-Group Elements?. J. Chem. Theory Comput. 2016, 12, 4303–4325. 10.1021/acs.jctc.6b00637. [DOI] [PubMed] [Google Scholar]
  28. Simón L.; Goodman J. M. How Reliable Are DFT Transition Structures? Comparison of GGA, Hybrid-Meta-GGA and Meta-GGA Functionals. Org. Biomol. Chem. 2011, 9, 689–700. 10.1039/C0OB00477D. [DOI] [PubMed] [Google Scholar]
  29. Becke A. D. Density-Functional Thermochemistry.III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652. 10.1063/1.464913. [DOI] [Google Scholar]
  30. Burke K. Perspective on Density Functional Theory. J. Chem. Phys. 2012, 136, 150901–150909. 10.1063/1.4704546. [DOI] [PubMed] [Google Scholar]
  31. Hohenberg P.; Kohn W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864–B871. 10.1103/PhysRev.136.B864. [DOI] [Google Scholar]
  32. Kohn W.; Sham L. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, A1133–A1138. 10.1103/PhysRev.140.A1133. [DOI] [Google Scholar]
  33. McLean A. D.; Chandler G. S. Contracted Gaussian Basis Sets for Molecular Calculations. I. Second Row Atoms, Z = 11–18. J. Chem. Phys. 1980, 72, 5639–5648. 10.1063/1.438980. [DOI] [Google Scholar]
  34. Hratchian H. P.; Schlegel H. B. Accurate Reaction Paths Using a Hessian Based Predictor-Corrector Integrator. J. Chem. Phys. 2004, 120, 9918–9924. 10.1063/1.1724823. [DOI] [PubMed] [Google Scholar]
  35. Frisch M. J.; Trucks G. W.; Schlegel H. B.; Scuseria G. E.; Robb M. A.; Cheeseman J. R.; Scalmani G.; Barone V.; Petersson G. A.; Nakatsuji H.; Li X.; Caricato M.; Marenich A. V.; Bloino J.; Janesko B. G.; Gomperts R.; Mennucci B.; Hratchian H. P.; Ortiz J. V.; Izmaylov A. F.; Sonnenberg J. L.; Williams-Young D.; Ding F.; Lipparini F.; Egidi F.; Goings J.; Peng B.; Petrone A.; Henderson T.; Ranasinghe D.; Zakrzewski V. G.; Gao J.; Rega N.; Zheng G.; Liang W.; Hada M.; Ehara M.; Toyota K.; Fukuda R.; Hasegawa J.; Ishida M.; Nakajima T.; Honda Y.; Kitao O.; Nakai H.; Vreven T.; Throssell K.; Montgomery J. A. Jr.; Peralta J. E.; Ogliaro F.; Bearpark M. J.; Heyd J. J.; Brothers E. N.; Kudin K. N.; Staroverov V. N.; Keith T. A.; Kobayashi R.; Normand J.; Raghavachari K.; Rendell A. P.; Burant J. C.; Iyengar S. S.; Tomasi J.; Cossi M.; Millam J. M.; Klene M.; Adamo C.; Cammi R.; Ochterski J. W.; Martin R. L.; Morokuma K.; Farkas O.; Foresman J. B.; Fox D. J.. Gaussian 09, revision D.01; Gaussian, Inc.: Wallingford CT, 2009.
  36. Dennington R.; Keith T. A.; Millam J. M.. GaussView 5, version 5.0.8, Shawnee Mission; Semichem Inc, 2009.

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao8b01003_si_001.pdf (614.8KB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES