Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part IV
Abstract
:1. Introduction
2. Experimental Data and Computational Methods
2.1. Experimental Data
j = 1,N
2.2. Computational Methods
3. Breakdown of the GC Approach When Achieving Chemical Accuracy
3.1. Ring Strain
3.1.1. Ring Strain Evaluated from Group Contribution Involving Experimental Heats of Formation
Σ Group Contribution of constituting Groups + strain energy
Cycloalkanes/Cycloalkenes | Exp. Rossini et al. [31,32,33,34,35,36] | Exp. Origin see Table S3 | Model dHf | Model-Exp + G4 Ring Strain | G4 Ring Strain | G4 dHf | Boltzmann-Averaged G4 dHf | Final Model-Exp. (or G4) |
---|---|---|---|---|---|---|---|---|
cyclopropane | 53.3 ± 0.6 | −61.89 | 0.2 | 115.4 | 53.7 | −0.6 | ||
cyclobutane | 28.4 ± 0.6 | −82.52 | −0.9 | 110.0 | 27.8 | −0.3 | ||
cyclopentane | −77.3 ± 0.8 | −103.15 | 3.6 | 29.4 | −73.4 | 0.7 | ||
cyclohexane | −123.2 ± 0.8 | −123.78 | 0.6 | 1.2 | −121.1 | −4.2 | ||
methylcyclopropane | 25.0 | −91.62 | −0.6 | 116 | 24.3 | −0.9 | ||
ethylcyclopropane | 3.2 | −112.25 | −1.1 | 114.4 | 2.1 | 2.3 | 3.8 | |
propylcyclopropane | −132.88 | 0.0 | 113.5 | −19.4 | −18.4 | 1.5 | ||
isopropylcyclopropane | −137.98 | 4.3 | 113.2 | −29.1 | −28.4 | 6.1 | ||
methylcyclobutane | −6.8 | −112.25 | 1.1 | 106.5 | −5.8 | −5.0 | −4.2 | |
ethylcyclobutane | −26.3 | −132.88 | −1.8 | 104.8 | −28.1 | −27.1 | −2.5 | |
propylcyclobutane | −153.51 | −0.1 | 103.7 | −49.7 | −47.9 | −1.5 | ||
isopropylcyclobutane | −158.61 | 4.3 | 102.9 | −60.0 | −59.0 | 3.7 | ||
methylcyclopentane | −106.7 ± 0.8 | −132.88 | 1.5 | 27.7 | −102.4 | −102.7 | −4.0 | |
ethylcyclopentane | −127.1 ± 1.0 | −153.51 | 0.8 | 27.2 | −126.2 | −125.7 | −0.8 | |
propylcyclopentane | −148.2 ± 1.3 | −174.14 | −0.1 | 25.8 | −148.1 | −147.4 | 0.5 | |
isopropylcyclopentane | −179.24 | 4.2 | 27.5 | −155.9 | −153.6 | 3.2 | ||
methylcyclohexane | −154.9 ± 1.0 | −153.51 | 0.0 | −1.4 | −154.8 | −2.2 | ||
propylcyclohexane | −193.4 ± 1.3 | −194.77 | −2.4 | −0.9 | −195.4 | −194.3 | −3.0 | |
isopropylcyclohexane | −199.87 | 4.1 | 6.4 | −197.6 | −197.5 | −5.9 | ||
1,1-dimethylcyclopropane | −8.2 ± 1.2 | −123.98 | 1.6 | 114.1 | −11.5 | 2.5 | ||
cis-1,2-dimethylcyclopropane | 0.7 | −117.55 | 3.8 | 122.1 | 0.3 | −2.8 | ||
trans-1,2-dimethylcyclopropane | −3.2 | −117.55 | 2.0 | 116.3 | −5.4 | 2.9 | ||
1,1-dimethylcyclobutane | −143.61 | 2.6 | 104.1 | −42.1 | 0.8 | |||
cis-1,2-dimethylcyclobutane | −138.18 | 4.2 | 109.1 | −33.3 | −2.9 | |||
trans-1,2-dimethylcyclobutane | −138.18 | 4.1 | 102.2 | −40.1 | 3.7 | |||
cis-1,3-dimethylcyclobutane | −138.18 | 4.1 | 103.4 | −38.9 | 3.0 | |||
trans-1,3-dimethylcyclobutane | −138.18 | 4.2 | 106.9 | −35.5 | −0.4 | |||
1,1-dimethylcyclopentane | −138.3 ± 1.2 | −165.24 | −0.2 | 26.7 | −140.1 | −139.4 | −0.4 | |
1,2-dimethylcyclopentane cis | −129.5 ± 1.3 | −158.81 | 2.2 | 31.5 | −131.4 | −130.2 | −2.8 | |
1,3-dimethylcyclopentane trans | −135.9 ± 1.2 | −158.81 | 5.1 | 28 | −134.8 | 3.6 | ||
1,2-dimethylcyclopentane trans | −136.7 ± 1.3 | −158.81 | 3.3 | 25.4 | −137.5 | 4.4 | ||
1,3-dimethylcyclopentane cis | −133.7 ± 1.5 | −158.81 | 1.8 | 26.9 | −136 | 1.4 | ||
cis-1,3-dimethylcyclohexane | −179.44 | 4.0 | −4 | −187.4 | 4.4 | |||
trans-1,4-dimethylcyclohexane | −179.44 | 4.1 | −3.6 | −187.1 | 4.1 | |||
cis-1,3,5-trimethylcyclohexane | −212.97 | 0.5 | −6.5 | −220 | 3.4 | |||
methylenecyclopropane | 201 | 28.74 | −4.0 | 157.7 | 190.4 | |||
methylenecyclobutane | 121.6 | 8.11 | 3.3 | 116.8 | 120.3 | |||
methylenecyclopentane | 12 ± 1.1 | −12.52 | 2.6 | 27.1 | 10.0 | |||
cyclopropene | 277 | 50.87 | −0.9 | 230.4 | 282.2 | |||
cyclobutene | 157 | 30.24 | −0.1 | 130.1 | 160.4 | |||
cyclopentene | 33 | 9.61 | 1.9 | 25.3 | 35.1 | |||
cyclohexene | −5.3 | −11.02 | 0.0 | 5.7 | −5 | |||
4-methylcyclopentene | −16.12 | 4.2 | 25.6 | 5.3 | 5.1 | |||
3-methylcyclopentene | 8 ± 2 | −16.12 | 0.4 | 24.5 | 5.1 | 5.7 | ||
1-methylcyclopentene | −4 ± 2 | −3.80 | −32.75 | −5.3 | 23.5 | −4.4 | ||
1-methylcyclopropene | 243.6 | 8.51 | −5.6 | 223.9 | 238.0 |
3.1.2. Discussion and Conclusions on How to Tackle Ring Strain
- -
- The isopropylcycloalkanes seem systematically off the GC prediction by 4.2 kJ/mol (Table 1, column 5). The Boltzmann-averaged G4 enthalpies did show some improvement but not for all. One could introduce an additional parameter correcting all isopropylalkanes by 4.2 kJ/mol and obtain very good agreement between the model and the experiment. However, as the deviation is not much beyond chemical accuracy and we do not have more than four experimental values, it seems more appropriate to suggest further studies including other substituted cycloalkanes before introducing an additional parameter. Therefore, at present, the isopropylalkanes are excluded from the conclusions on the other cycloalkanes discussed below.
- -
- For cyclopropane, a single alkyl substitution has a small influence on the ring strain, which is around 115 kJ/mol independent of the alkyl chain length. When we consider all cyclopropanes in Table 1, we do not see very large deviations. It should be mentioned here that, in part, we cannot compare with experimental data and need to rely on a mix of experimental and G4-calculated data. When we take the GC model value and add a ring strain of 115 kJ/mol for all substituted cyclopropanes, we obtain heats of formation within chemical accuracy from the G4-computed result. This even applies for cis-1,2-dimethylcyclopropane for which the G4 ring strain as such was calculated as 122 kJ/mol and therewith is clearly larger than for all other cyclopropanes.
- -
- For cyclobutane, the ring strain slowly drops with the lengthening of the alkyl chain, 6 kJ/mol from cyclobutane up till propylcyclobutane, but levels off with longer alkyl chain length. For the mono- and di-methyl-substituted cyclobutanes, the ring strain is roughly constant and around 103 kJ/mol. Again, the exception is cis-1,2-dimethylcyclobutane, with a G4-calculated ring strain of 109.1 kJ/mol being somewhat higher than those for other substituted cyclobutanes, but the overall result is still, albeit just, within chemical accuracy. The GC model does not (yet) discriminate between cis and trans in the current context. Still, when we take the GC model value and add a ring strain of 102.5 kJ/mol for the substituted cyclobutanes, we obtain a heat of formation within chemical accuracy from the G4-computed result. Only cyclobutane itself needs to be considered separately, but this is not a problem because for the isolated species, we can adopt the experimental value anyway.
- -
- For cyclopentane, the ring strain is almost constant with the lengthening of the alkyl chain.
- -
- For both the mono- as well as the dimethylcyclopentanes, we see pretty good agreement (column 4 in Table 1), but the G4 strain energies vary. Here, we observed a somewhat higher value for the G4-calculated ring strain for cis-1,2-dimethylcyclopentane. When we add to the pure GC approach, a strain energy of 26.5 kJ/mol throughout, we obtain chemical accuracy for all named species. Note that for most species, we rely on available experimental heat of formation data.
- -
- For the alkyl-substituted cyclohexanes, we observe similar trends as for the cyclopentanes: the results presented in Table 6 in [7] reveal, upon considering our GC model, that we find a very constant ring strain of −2 kJ/mol (note that it is indeed a minus sign!) for the series methylcyclohexane up till tetradecylcyclohexane, compared to 0.4 kJ/mol for the parent cyclohexane. Interestingly, the G4 results also suggest a small but negative ring strain for n-alkylcyclohexanes (see Table 1).
3.2. Selection of the Group Size: Problems with Systems Not Obeying ’Simple’ GC
3.3. Steric Hindrance
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Pyridines and Quinolines | Verevkin et al. [28] | Model dHf | Model-Exp | ABS (Model-Exp) |
---|---|---|---|---|
pyridine | 140.4 ± 0.7 | 142 * | 1.60 | 1.60 |
2-methylpyridine | 99.2 ± 0.8 | 99.64 | 0.44 | 0.44 |
3-methylpyridine | 106.4 ± 0.6 | 105.64 | −0.76 | 0.76 |
4-methylpyridine | 104.1 ± 0.9 | 105.64 | 1.54 | 1.54 |
2,3-dimethylpyridine | 68.3 ± 14 | 63.28 | −5.02 | 5.02 |
2,4-dimethylpyridine | 63.9 ± 0.9 | 63.28 | −0.62 | 0.62 |
2,5-dimethylpyridine | 66.5 ± 1.1 | 63.28 | −3.22 | 3.22 |
2,6-dimethylpyridine | 58.7 ± 1.6 | 57.28 | −1.42 | 1.42 |
3,4-dimethylpyridine | 70.7 ± 1.1 | 75.78 | 5.08 | 5.08 |
3,5-dimethylpyridine | 72.8 ± 1.0 | 75.78 | 2.98 | 2.98 |
2-ethylpyridine | 75.6 ± 3.5 | 79.01 | 3.41 | 3.41 |
3-ethylpyridine | 82.9 ± 3.5 | 85.01 | 2.11 | 2.11 |
4-ethylpyridine | 80.6 ± 3.5 | 85.01 | 4.41 | 4.41 |
quinoline | 200.5 ± 1.0 | 197 * | −3.50 | 3.50 |
2-methylquinoline | 156.6 ± 0.9 | 160.64 | 4.04 | 4.04 |
4-methylquinoline | 158.6 ±2.7 | 160.64 | 2.04 | 2.04 |
6-methylquinoline | 157.3 ± 2.4 | 160.64 | 3.34 | 3.34 |
8-methylquinoline | 164.8 ± 1.3 | 160.64 | −4.16 | 4.16 |
2,6-dimethylquinoline | 121.3 ± 0.9 | 124.28 | 2.98 | 2.98 |
2,7-methylquinoline | 119.8 ± 3.1 | 124.28 | 4.48 | 4.48 |
2-phenylquinoline | 286.6 ± 4.5 | 287.5 | 0.90 | 0.90 |
averaged absolute difference | 2.76 |
Experimental dHf Difference kJ/mol | DFT Calculated Energy Difference kJ/mol | |
---|---|---|
2-methylhexane and 3-methylhexane | 2.7 | 4.5 |
2,2-dimethylhexane and 2,3-dimethylhexane | 10.8 | 10.0 |
2,2-dimethylhexane and 2,4-dimethylhexane | 5 | 2.8 |
2,2-dimethylhexane and 2,5-dimethylhexane | 2 | −1.5 |
2,3-dimethylhexane and 2,4-dimethylhexane | 5.5 | 7.2 |
2,2,5-trimethylhexane and 2,3,4-trimethylhexane | 19 | 18.8 |
2,2,3,3,4-pentamethylpentane and 2,2,3,4,4-pentamethylpentane | 0.2 | 1.7 |
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Meier, R.J.; Rablen, P.R. Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part IV. Thermo 2023, 3, 289-308. https://doi.org/10.3390/thermo3020018
Meier RJ, Rablen PR. Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part IV. Thermo. 2023; 3(2):289-308. https://doi.org/10.3390/thermo3020018
Chicago/Turabian StyleMeier, Robert J., and Paul R. Rablen. 2023. "Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part IV" Thermo 3, no. 2: 289-308. https://doi.org/10.3390/thermo3020018