(427c) Ring Additivity Group (RAG) Values for Thermochemical Properties of Unsubstituted Polycyclic Aromatic Hydrocarbons (PAH) Via Computational Chemistry

Numerical values have been determined for 8 of the 12 aromatic ring additivity groups (RAG) used for determining the standard heat of formation (ΔH_f°), entropy (S°), and heat capacities (C_p°) of planar benzenoid PAH (polycyclic aromatic hydrocarbons) via AM1-UHF and STO-3G B3LYP calculations. These RAG values are used in lieu of groups from other group contribution (GC) methods, as described in previous work [1].

This study considered the three series of planar benzenoid PAH [2] used in estimations of corresponding-states properties (critical properties, the acentric factor), normal boiling points, and Lennard-Jones parameters [3-6]:

(1) linear acenes: kata-condensed benzenoid PAH (C_2+4nH_4+2n). The first four compounds beyond benzene in this series are naphthalene, anthracene, tetracene, and pentacene.

(2) zig-zag acenes: kata-condensed benzenoid PAH (C_2+4nH_4+2n). The first four compounds beyond benzene in this series are naphthalene, phenanthrene, chrysene, and picene.

(3) peri-condensed PAH: benzenoid PAH which have tightly packed ring structures (like chicken wire), including the one-isomer series of Dias [7]. This series of PAH is representative of those found under combustion, pyrolysis, and gasification conditions [8].

The transfer function between that of Gutman et al. [9], Gutman and Cyvin [10], and that which is used here [1] is as follows:

Ref. 9	Ref. 10	Ref. 1
1	L1	H1
2	P2	H2-3
3	A2	H2-5
4	L2	H2-9
5	L3	H3-7
6	P3	H3-11/13
7	A3	H3-21
8	P4	H4-15
9	L4	H4-23
10	A4	H4-27
11	L5	H5
12	L6	H6

Fitting of the RAG values from the computed thermochemical properties was done in stages. The calculated values for the linear and zig-zag PAH were used to fit groups H2-9 and H2-5, respectively. The one-isomer peri-condensed PAH starting with coronene (C₂₄H₁₂) yielded the values for H3-7, H4-15, and H6. The peri-condensed PAH between the one-isomer compounds were used for fitting H2-3, H4-23, and H5. The H1 values obtained from each of the three PAH series showed the possible need for second-order corrections. Results were also fit using a ln(K) term, where K is the number of Kekulé resonance structures, in the manner of Herndon et al. [11].

Future work will consider different kata-condensed and peri-condensed PAH structures, including those containing the four planar benzenoid RAGs not appearing in the PAH considered to date, i.e., H2-9, H3-11/13, H3-21, and H4-27. Computational chemistry methods will generate thermochemical properties for fitting those RAG values. Once there is sufficient confidence in the planar PAH RAG values, the approach with be extended to (1) mono-substituted benzenoid PAH and (2) unsubstituted PAH containing both 6- and 5-membered rings.

References:

[1] Pope, C. (2016) "Demonstration of the Equivalence of Ring-Additivity and Group-Contribution Methods for Properties of Unsubstituted Polycyclic Aromatic Hydrocarbons (PAH)", paper presented at the American Institute of Chemical Engineers Annual Meeting, November 2016, San Francisco, CA. See also references cited therein. https://aiche.confex.com/aiche/2016/webprogram/Paper457265.html

[2] Pope, C. (2015) "Estimation of Diffusion Coefficients of Polycyclic Aromatic Hydrocarbons (PAH) and Fullerenes", poster presented at the American Institute of Chemical Engineers Annual Meeting, November 2015, Salt Lake City, UT. See also references cited therein. https://aiche.confex.com/aiche/2015/webprogram/Paper427453.html

[3] Pope, C.J. "Estimation of Normal Boiling Point, Critical Properties, and Lennard-Jones ---Parameters for Polycyclic Aromatic Hydrocarbons and Fullerenes", poster presented at the American Institute of Chemical Engineers Annual Meeting, November 2013, San Francisco, CA. https://aiche.confex.com/aiche/2013/webprogram/Paper311280.html

[4] Pope, C.J. "Revisiting Approaches to Obtaining Transport Properties of PAH and Fullerenes", poster presented at the Thirty-Fifth Symposium (International) on Combustion, August 2014, San Francisco, CA.

[5] Pope, C.J. "Estimation of the Acentric Factor for Polycyclic Aromatic Hydrocarbons (PAH) and Fullerenes", poster presented at the American Institute of Chemical Engineers Annual Meeting, November 2014, Atlanta, GA. https://aiche.confex.com/aiche/2014/webprogram/Paper387336.html

[6] Pope, C.J. "Application of the Marrero and Pardillo Property Estimation Method to Unsubstituted Polycyclic Aromatic Hydrocarbons (PAH) and Fullerenes", poster presented at the American Institute of Chemical Engineers Annual Meeting, November 2014, Atlanta, GA. https://aiche.confex.com/aiche/2014/webprogram/Paper381211.html

[7] Dias, J.R. (1987) "Handbook of Polycyclic Hydrocarbons Part A: Benzenoid Hydrocarbons", Elsevier, New York, pp. 122-123.

[8] Pope, C.J. (1988) "Fluxes and Net Reaction Rates of High Molecular Weight Material in a Near-Sooting Benzene-Oxygen Flame", S.M. Thesis, Massachusetts Institute of Technology.

[9] Gutman, I.; Furtula, B.; Radenković, S. (2004) "Relation between Pauling and Coulson Bond Orders in Benzenoid Hydrocarbons, Z.Naturforsch., 59a:699-704.

[10] Gutman, I.; Cyvin, S.J. (1989) "Introduction to the Theory of Benzenoid Hydrocarbons", Springer-Verlag, New York.

[11] Herndon, W. C.; Nowak, P. C.; Connor, D. A.; Lin, P. (1992) "Empirical Model Calculations for Thermodynamic and Structural Properties of Condensed Polycyclic Aromatic Hydrocarbons", J.Am.Chem.Soc., 114:41−47.