Comment/Reply pubs.acs.org/jced
Comment on “Use of G4 Theory for the Assessment of Inaccuracies in Experimental Enthalpies of Formation of Aliphatic Nitro Compounds and Nitramines” Marina A. Suntsova and Olga V. Dorofeeva* Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia S Supporting Information *
I
n our recently published paper1 we have provided a reference data set of internally consistent gas-phase enthalpies of formation of nitro compounds and nitramines. Among these are the cyclic nitramines (42−48). In the later, more detailed study of 48,2 it was found that the enthalpy of formation of 48 predicted using the isodesmic reactions involving cyclic nitramines 42−47 is on average 23 kJ·mol−1 less than that estimated from isodesmic reactions without cyclic nitramines. Our experience in isodesmic reaction calculations at the G4 and G4(MP2) levels tells us that this difference is too large to be attributed to the use of different types of reactions. Most probably, this difference is caused by the underestimated ΔfH298 ° (g) values for 42−47. This assumption was confirmed by the new isodesmic reaction calculations which include a large number of reactions not involving cyclic nitramines (Table S1 of Supporting Information). On the basis of these calculations, new ΔfH298 ° (g) values are recommended for 42−48. A modified part of Table 2 from ref 1, in which the previously recommended values have been changed, is presented in this comment. The new recommended value of ΔfH°298(42, g) = −37.0 ± 4.0 kJ·mol−1 agrees, within its uncertainty, with the experimental value of −40.2 ± 2.1 kJ·mol−1 which was accepted in ref 1. However, the use of this theoretical value in the isodesmic reactions for other cyclic nitramines shifts the enthalpies of formation of 43−48 to more positive values compared to these in ref 1. Because these more positive values agree well with the values calculated from isodesmic reactions not involving cyclic nitramines (see Table S1 of Supporting Information), we recommend them in Table 2 of this comment as more reliable estimates of enthalpy of formation of 42−48. The changes have also affected the G4 energies of 42 and 44 used in isodesmic reactions calculations. The optimized B3LYP/ 6-31G(d,p) geometries of the most stable conformers were used as inputs for further G4 calculations.1 However, it was found that the order of the conformer energies for the B3LYP/6-31G(d,p) and G4 theory is a little different for 42 and 44. The use of lower G4 energies for 42 and 44 led to an additional changes up to 1.5 kJ·mol−1 in the calculated enthalpies of formation. Table S1 of Supporting Information shows that the new recommended ΔfH°298(g) values for 42−48 are in internal consistency with each other and with reliable experimental enthalpies of formation for a large number of reference compounds including cycloalkanes, nitrogen heterocycles, noncyclic nitro compounds, and nitramines. It should also be noted that the values calculated in this work using isodesmic reactions are in fairly good agreement with the G4(MP2) and M06-2X/ccpVTZ values calculated from atomization reactions (Table 1) (in contrast to G4, the G4(MP2) and M06-2X/cc-pVTZ methods © 2015 American Chemical Society
Table 1 isodesmic reactions
atomization reaction
compound
G4 or G4(MP2) for 47 and 48
G4(MP2)
M06-2X/cc-pVTZ
42 43 44 45 46 47 48
−37.1 64.7 114.1 190.8 144.7 247.7 522.8
−34.4 68.3 118.1 196.2 152.3 253.9 523.1
−31.7 66.1 116.4 193.8 141.8 237.2 552.7
when applied to atomization reactions show quite good agreement with experimental data for other nitro compounds).
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ASSOCIATED CONTENT
* Supporting Information S
The enthalpies of formation of 42−48 calculated from a large number of isodesmic reactions (Table S1). This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Funding
This research was supported by the Russian Foundation for Basic Research under Grant No. 14-03-00612. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Dorofeeva, O. V.; Suntsova, M. A. Use of G4 Theory for the Assessment of Inaccuracies in Experimental Enthalpies of Formation of Aliphatic Nitro Compounds and Nitramines. J. Chem. Eng. Data 2014, 59, 2813−2826. (2) Dorofeeva, O. V.; Suntsova, M. A. Enthalpy of Formation of CL-20. Comput. Theor. Chem. 2015, 1057, 54−59. (3) Sinditskii, V. P.; Egorshev, V. Yu.; Serushkin, V. V.; Levshenkov, A. I.; Berezin, M. V.; Filatov, S. A.; Smirnov, S. P. Evaluation of decomposition kinetics of energetic materials in the combustion wave. Thermochim. Acta 2009, 496, 1−12.
Received: February 18, 2015 Accepted: April 16, 2015 Published: April 27, 2015 1532
DOI: 10.1021/acs.jced.5b00159 J. Chem. Eng. Data 2015, 60, 1532−1533
Journal of Chemical & Engineering Data
Comment/Reply
Table 2. Enthalpies of Formation (ΔfH298 ° ) in Both Condensed and Gaseous Phases and Enthalpies of Sublimation (ΔsubH298 ° ) or Vaporization (ΔvapH°298) of Aliphatic Nitro Compounds*
*
Reference numbers are cited from the original paper. aValues calculated from isodesmic reactions are given. bCalculated in this work using the ° (l) + ΔvapH298 ° = ΔfH298 ° (g) or ΔfH298 ° (cr) + ΔsubH298 ° = ΔfH298 ° (g). relationships between condensed and gas phase enthalpies of formation: ΔfH298 c Reference 42 in original paper. dReference 64 in original paper. eG4(MP2) energies were used in the isodesmic reaction calculations. fSuggested from the analysis of available experimental phase transition data, ref 3 in this comment. gBased on the thermocouple measurements data, ref 3 in this comment. hCalculated in this work using ΔfH°298(cr) = 377.4 kJ/mol. Reference 69 in original paper.
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DOI: 10.1021/acs.jced.5b00159 J. Chem. Eng. Data 2015, 60, 1532−1533
