Supplementary material
Energetic effects of alkyl groups (methyl and ethyl) on the nitrogen of morpholine molecule
Vera L. S. Freitas*, Carlos A. O. Silva, Mónica A. T. Paiva, Maria D. M. C. Ribeiroda SilvaCentro de InvestigaçãoemQuímica, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal
Table of Contents
PageS1. / Purification ...... / S3
S2. / Combustion calorimetry …………..…………………………………………………..………………….. / S4
S3. / Vacuum drop microcalorimetric technique ……..………………………………………………………... / S8
S4. / Computational studies – G3(MP2)//B3LYP method ………………………………………….…………. / S11
Table Index
PageTable S1. / Source details of the materials used and purification information and analysis of N-methylmorpholine and N-ethylmorpholine...... / S3
Table S2. / Typical combustion results and standard (p = 0.1 MPa) massic energy of combustion, at T = 298.15 K, for N-methylmorpholine...... / S6
Table S3. / Typical combustion results and standard (p = 0.1 MPa) massic energy of combustion, at T = 298.15 K, for N-ethylmorpholine...... / S7
Table S4. / Calvet microcalorimetry results for the process of vaporization of N-methylmorpholine...... / S9
Table S5. / Calvet microcalorimetry results for the process of vaporization of N-ethylmorpholine...... / S10
Table S6. / Absolute standard enthalpies, , and entropies, , obtained by G3(MP2)//B3LYP composite method for the two most stable conformers of N-methylmorpholine, and the corresponding derived gas-phase standard molar enthalpies, , entropies, , and Gibbs energy of formation, , at T = 298.15 K, and the conformational composition, i...... / S12
Table S7. / Absolute standard enthalpies, , and entropies, , obtained by G3(MP2)//B3LYP composite method for the two most stable conformers of N-ethylmorpholine, and the corresponding derived gas-phase standard molar enthalpies, , entropies, , and Gibbs energy of formation, , at T = 298.15 K, and the conformational composition, i...... / S13
Table S8. / G3(MP2)//B3LYP enthalpies, , with corresponding conformer composition (in parentheses and boldface), and experimental gas-phase standard (pº = 0.1 MPa) molar enthalpies of formation, , at T = 298.15 K, for N-methylmorpholine and N-ethylmorpholine conformers and for the auxiliary species………………………………………………………... / S14
Table S9. / Standard (pº = 0.1 MPa) molar heat capacities in the gaseous phase for
N-methylmorpholine and N-ethylmorpholine, derived from statistical thermodynamics using the vibrational frequencies calculated at the B3LYP/6-31G(d) level of theory (scaled by a factor of 0.960 0.022)...... / S16
Throughout this paper, the standard state (and thus any standard thermodynamic property) of a pure liquid refers to the pure substance in the liquid phase under the pressureof p = 0.1 MPa. When the substance is a pure gas, its standard state is that of an ideal gas at p of 0.1 MPa (or, which is equivalent, that of a real gas at p = 0). Standard states will be denoted by a superscript “o”.
The relative atomic masses used throughout this paper were those suggested by the IUPAC Commission in 2013 [[1]].
S1
S1. Purification
The purity control of the samples was carried out by gas-liquid chromatography, using an Agilent 4890 apparatus equipped with an HP-5 column, cross-linked, 5% diphenyl and 95% dimethylpolysiloxane (15 m0.530 mmi. d. 1.5 μm film thickness), and by the ratio of carbon dioxide recovered during the combustion experiments (gravimetric analysis results are given in tables S2 and S3).
Table S1 Source details of the materials used and purification information and analysis of N-methylmorpholine and N-ethylmorpholine.
Chemical Name / CAS Registry No. / Source / Initial purity / Purification method / Final massfraction purity
N-methylmorpholine / 109-02-4 / Sigma-Aldrich / 0.9991a / Vacuum distillation / 0.9995b
1.0001 0.0002c
N-ethylmorpholine / 100-74-3 / TCI / 0.969a / Vacuum distillation / 0.9990b
Benzoic acid / 65-85-0 / NIST / 0.999996a / /
Decane / 124-18-5 / Sigma-Aldrich / 0.990a / /
aValues stated in the certificate of analysis of the supplier;
b Mass fraction purities obtained from gas-liquid chromatography;
cResults obtained from combustion calorimetry, based on mass fraction of carbon dioxide recovery (mean and standard deviation of the mean for six experiments).
S1
S2. Combustion calorimetry
The combustion experiments of the organic nitrogen compounds were performed with an isoperibol calorimeter [[2]-[3][4]]. This calorimeter has a twin valve bomb, with an internal volume of 0.290 dm3 made of stainless steel (with a wall thickness of 1 cm).The calorimetric system was calibrated using benzoic acid Standard Reference Material (SRM) 39j supplied by National Institute of Standards & Technology [[5]], having a massic energy of combustion of (26434 ± 3) J·g-1, when burned under certificate conditions. For each calibration experiment,1.00 cm3 of desionized water was added to the bomb, and the bomb was flushed and charged to 3.04 MPawith pure oxygen (). The calibration results were corrected to give the energy equivalent, , corresponding to the average mass of water added to the calorimeter of 2900.0 g. One set of six calibration experiments was performed leading to the value of the energy equivalent of the calorimeter, = (15551.2 ± 1.6) J·K-1, where the standard uncertainty quoted is the estimated standard deviation of the mean.
The liquid samples were enclosed in polyester bags made of Melinex® (0.025 mm thickness), using the technique described by Skinner and Snelson [[6]].In each experiment, the sample and the auxiliary were introduced in a platinum crucible inside the bomb and in contact with a cotton thread fuse attached to the platinum ignition wire (Goodfellows, = 0.05 mm). All weighs were performed in a Mettler AE240, with a precision ± (110-5) g. The combustion bomb was flushed and filled with pure oxygen () until reaching a pressure of 3.04 MPa and, approximately, 2900.0 g of water were introduced inside the calorimeter.The calorimeter temperature was measured to ± (110-4) K, at intervals of ten seconds using a S10 four wire calibrated ultra-stable thermistor probe (Thermometrics, standard serial No. 1030) and recorded by a high sensitivity nanovolt/microohm meter (Agilent 34420 A) interfaced to a computer programmed to compute the adiabatic temperature change, Tad. The samples were ignited at T = (298.150 ± 0.001) K, by the discharge of a 1400 F capacitor through the platinum ignition wire.
The combustion reactions for N-methylmorpholine (C5H11NO) and N-ethylmorpholine (C6H13NO) are represented by the following equations, respectively:
/ (S1)/ (S2)
The temperature profiles for each experiment were divided into three periods, fore-, main- and after-periods, each one with one hundred points at least. The energy of reaction was always referred to the initial temperature of 298.15 K. The accurate numerical calculation of the corrected temperature rise in the isoperibol calorimetry was carried out by means of the LABTERMO program [[7]] based in the method of calculation described by Coops et al. [[8]]. The electrical energy for the ignition U(ign) was determined from the change in potential difference across a 1400 μF capacitor through the platinum ignition wire.
The internal energy associated to the isothermal bomb process, , was calculated through eq. S3, in which is the calorimeter temperature change corrected for the heat exchange and the work of stirring, represents the difference between the mass of water added to the calorimeter and the mass of 2900.0 g assigned to , is the energy equivalent of the content in the final state, is the electric energy for the ignition, and is the massic heat capacity, at constant pressure, for liquid water.
/ (S3)After the calorimetric measurements the combustion products were analyzed:thecaobon dioxide (CO2) formed was collected in absorption tubes [[9]] and calculated from the increase in weight of the tubes by multiplying it by the factor 1.0045, previously derived by Rossini [[10]]; the nitric acid formed was determined by titration and the respective correction was based on 59.7 kJ·mol-1 (the molar energy of formation for 0.1 mol·dm-3 HNO3 (aq) from N2 (g), O2 (g) and H2O (l) [[11]]). The cotton thread used has an empirical formula CH1.686O0.843 and a massic energy of combustion 16240 J·g-1[8], a value previously confirmed in our laboratory. In the case of Melinex, it was considered the standard massic energy of combustion of dry Melinex = (22902 ± 5) J·g-1 [6]. This value was confirmed by combustion of Melinex samples in our laboratory. The mass of Melinex used in each experiment was corrected for the mass fraction of water (0.0032).
For the experiments with a small carbon soot residue formed during the combustion, the necessary energetic correction for its formation was based on standard molar energy of combustion of 33 kJmol-1 [11].
The value for the pressure coefficient of specific energy , was assumed to be
0.2 J·g-1·MPa-1, at T = 298.15 K, a typical value for most organic compounds [[12]].The mass of compound, m(cpd)used in each experiment was determined from the total mass of CO2produced after allowance for that formed from the Melinex.
The reduction of weight in air to mass in vacuum was made using specific densities: 0.92 gcm-3 for
N-methylmorpholine [[13]] and 0.91 gcm-3 for N-ethylmorpholine [[14]]. The standard massic energies of combustion of the compounds,, were calculated according to the procedure given by Hubbard et al. [[15]].
The results for typical combustion experiments and the individual values of, together with the mean and the estimated standard deviation of the mean, for N-methylmorpholineand
N-ethylmorpholine are given in Tables S2 and S3, respectively.
S1
Table S2Typical combustion results and standard (p = 0.1 MPa) massic energy of combustion, at T = 298.15 K, for N-methylmorpholine.a
Experiment / 1 / 2 / 3 / 4 / 5 / 6m (CO2, total) / g / 1.74688 / 1.84867 / 1.47548 / 1.68892 / 1.45580 / 1.47456
m (cpd) / g / 0.68390 / 0.73197 / 0.57709 / 0.58663 / 0.56842 / 0.57982
m (fuse) / g / 0.00299 / 0.00213 / 0.00253 / 0.00263 / 0.00229 / 0.00287
m (Melinex) / g / 0.11099 / 0.11038 / 0.09427 / 0.17858 / 0.09409 / 0.09104
m (carbon) / g / 0 / 0 / 0 / 0.00015 / 0 / 0
Tad / K / 1.61767 / 1.71966 / 1.36733 / 1.51144 / 1.34849 / 1.36761
f / (J·K-1) / 15.70 / 15.85 / 15.25 / 15.45 / 15.23 / 15.26
m (H2O) / g / 2.0 / 0.2 / 1.4 / 1.0 / 0.5 / 0
U (IBP) / J / 25194.96 / 26770.73 / 21275.73 / 23520.95 / 20993.26 / 24241.69
U (carbon) / J / 0 / 0 / 0 / 4.95 / 0 / 0
U (Melinex) / J / 2541.93 / 2528.00 / 2159.06 / 4089.89 / 2154.94 / 2085.04
U (fuse) / J / 48.56 / 34.59 / 41.09 / 42.71 / 37.19 / 46.61
U (HNO3) / J / 44.12 / 49.69 / 40.48 / 42.15 / 39.04 / 40.54
U (ign) / J / 0.68 / 0.74 / 0.73 / 0.78 / 0.74 / 0.65
U / J / 11.64 / 12.37 / 9.59 / 11.55 / 9.46 / 9.57
/ (J·g-1) / 32970.78 / 32987.80 / 32968.02 / 32967.29 / 32990.79 / 32952.36
/ 100.083 / 99.958 / 100.029 / 100.007 / 99.987 / 100.005
= (32972.8 ± 5.8) J·g-1,b
= (100.012 ± 0.017) b
aThe symbols presented in this table have the following meaning: m(CO2, total), mass of carbon dioxide; m(cpd), mass of compound; m(fuse), mass of fuse (cotton); m(Melinex), mass of Melinex; m(carbon), mass of carbon residue formed; Tad, corrected temperature rise; f, energy equivalent of the contents in the final state; m(H2O), deviation of mass of water added to the calorimeter from 2900.0 g; U(IBP), internal energy associated to the isothermal combustion reaction under actual bomb conditions (eq. S3); U(carbon), energy of combustion of carbon residue;U(Melinex), energy of combustion of Melinex; U(fuse), energy of combustion of the fuse (cotton); U(HNO3), energy correction for the nitric acid formation; U(ign), electric energy for the ignition; U, standard state correction; , standard (p = 0.1 MPa) massic energy of combustion for the compound; % CO2, percentage of carbon dioxide recovered;
bThe standard uncertainty corresponds to the estimated standard deviation of the mean for six experiments.
Table S3Typical combustion results and standard (p = 0.1 MPa) massic energy of combustion, at T = 298.15 K, for N-ethylmorpholine.a
Experiment / 1 / 2 / 3 / 4 / 5 / 6m (CO2, total) / g / 1.17972 / 0.95338 / 1.20530 / 1.21422 / 1.09061 / 1.18227
m (cpd) / g / 0.41191 / 0.31583 / 0.42219 / 0.42626 / 0.38297 / 0.42222
m (fuse) / g / 0.00268 / 0.00221 / 0.00200 / 0.00237 / 0.00219 / 0.00233
m (Melinex) / g / 0.10087 / 0.10015 / 0.10222 / 0.10178 / 0.09127 / 0.09191
m (carbon) / g / 0 / 0.00100 / 0 / 0 / 0 / 0
Tad / K / 1.06997 / 0.85399 / 1.09519 / 1.10430 / 0.99248 / 1.08065
f / (J·K-1) / 14.69 / 14.32 / 14.72 / 14.71 / 14.50 / 14.72
m (H2O) / g / 1.3 / 1.8 / 0.7 / 1.0 / 0.7 / 0
U (IBP) / J / 16659.66 / 13285.17 / 17049.65 / 17192.85 / 15450.36 / 16820.12
U (carbon) / J / 0 / 33.00 / 0 / 0 / 0 / 0
U (Melinex) / J / 2310.06 / 2293.61 / 2341.13 / 2331.08 / 2090.29 / 2104.91
U (fuse) / J / 43.52 / 35.89 / 32.48 / 38.49 / 35.57 / 37.84
U (HNO3) / J / 32.90 / 26.73 / 34.29 / 38.77 / 37.68 / 32.90
U (ign) / J / 1.20 / 1.20 / 1.20 / 1.20 / 1.19 / 1.19
U / J / 7.26 / 5.88 / 7.42 / 7.48 / 6.60 / 7.23
cuº (cpd) / (J·g-1) / 34633.57 / 34689.73 / 34662.89 / 34666.72 / 34676.93 / 34667.33
/ 99.784 / 99.866 / 99.770 / 99.212 / 99.697 / 99.670
= (34666.2 ± 7.6) J·g-1,b
aThe symbols presented in this table have the same meaning of the symbols of the above table;
bThe standard uncertainty corresponds to the estimated standard deviation of the mean for six experiments.
S1
S3. Vacuum drop-microcalorimetric technique
The standard (pº = 0.1 MPa) molar enthalpies of vaporization, , of the two
N-alkylmorpholine derivatives were determined by the vacuum drop-microcalorimetry technique. This technique was described by Skinner et al for the study of solids [[16]], for the determination of enthalpies of sublimation, which was adapted and tested for liquid vaporizations in our Laboratory [[17]].The measurements were carried out with a high temperature Calvet microcalorimeter (Setaram HT1000, Lyon, France) with the vacuum promoted by a rotary vacuum pump and a vapour diffusion pump. Both apparatus and technique have been already described in the literature [[18]].
The temperature, T, of the hot reaction vessel of the calorimeter was predefined for the vaporization study of each compound: 334 K for N-methylmorpholine and 376 K for N-ethylmorpholine. During the vaporization experiments of N-ethylmorpholine the cells of the calorimeter where filled with nitrogen, once the compound is hygroscopic. The samples (ranging from 4-6 mg) contained in thin glass capillary tubes sealed at one end, were dropped simultaneously with the corresponding blank tube at T = 298.15K into the hot reaction vessel in the Calvet microcalorimeter, held at the hot-zone temperature; after reached the thermostability, the sample is removed from the hot-zone by vacuum.The samples of the compound and the glass capillary tubes were weighed with a precision ± (110-6) g on a Mettler-Toledo UMT2 microbalance.
The blank heat capacity corrections for the glass capillary tubesand for the different sensibilities of the two measuring cells were determined in separate experiments.Individual blank correction experiments were performed by dropping tubes of nearly equal mass,between 20 and 25 mg to within (110-4) g, into each of the twin calorimetric cells. A blank heat capacity correction, as a function of the hot reaction vessel, T, and of the masses of the blank and of the experimental capillary tube, was obtained.
The microcalorimeter was calibrated in situfor the two predefined temperatures through the determination of the enthalpy of vaporization of decane, a recommended reference material, following a procedure identical to that described above for the compounds, using its values of the standard molar enthalpy of vaporization, at T = 298.15 K, = (51.4 0.2) kJmol-1 [[19]].The calibration constants determined for the experimental conditions of each of the compounds were: kcal(N-methylmorpholine) = (1.042 0.018) and kcal(N-ethylmorpholine) = (1.013 0.010); these constants were obtained as the average of five and six independent experiments, respectively, with the quoted standard uncertainty being the combined standard uncertainty which include the estimated standard deviation of the mean and the standard uncertainty associated with the reference value of the decane.
The Calvet microcalorimetry results obtained for the process of vaporization of the two compounds studied are given in tables S4 and S5.
Table S4 Calvet microcalorimetry results for the process of vaporization of N-methylmorpholine.a
Ensaio / 1 / 2 / 3 / 4 / 5 / 6TCalvet / Kb / 334.58 / 334.58 / 334.70 / 334.33 / 334.28 / 334.41
m(sct) / mg / 23.3665 / 22.2779 / 24.6631 / 22.2750 / 23.3794 / 21.5401
m(rct) / mg / 23.3723 / 22.3034 / 24.7906 / 22.3037 / 23.3809 / 21.5486
m(cpd) / mg / 5.825 / 5.698 / 5.488 / 4.820 / 6.450 / 5.738
H(blank) / mJ / 9.060 / 5.186 / 7.770 / 5.788 / 9.256 / 4.022
H(total) / J / 2.471 / 2.420 / 2.383 / 1.975 / 2.801 / 2.428
H(corr) / J / 2.462 / 2.415 / 2.375 / 1.970 / 2.792 / 2.424
(exp)/ kJmol-1 / 44.54 / 44.67 / 45.61 / 43.07 / 45.63 / 44.51
(g)/ kJ·mol-1 / 4.65 / 4.65 / 4.66 / 4.61 / 4.61 / 4.62
(298.15 K) / kJ·mol-1 / 39.9 / 40.0 / 40.9 / 38.5 / 41.0 / 39.9
(298.15 K) = 40.03.1kJ·mol-1,c
aThe symbols presented in this table have the following meaning: TCalvet, temperature of the hot reaction vessel; m(sct) mass of the sample capillary tube; m(rct) mass of the reference capillary tube; m(cpd), mass of the compound; H(blank), blank heat capacity corrections for the glass capillary tubes; H(total), total enthalpy calculated from the area of the enthalpic peak obtained in the experiment; H(corr), enthalpy change corrected taking into account the blank experiments, calculated from H(corr) = H(total) + H(blank); (exp), enthalpy of vaporization from 298.15 K to temperature of the hot reaction vessel calculated from , where is the calibration constant of the calorimeter for the experimental conditions and M the molar mass of the compound; (g), enthalpy change in the gas-phase phase from 298.15 K to the temperature of the hot reaction vessel; (298.15 K), enthalpy of vaporization at 298.15 K of the compound calculated from
= .
bThe standard uncertainty of the temperature measurements is u(T/K) = 0.01.
cThe standard uncertainty corresponds to the expanded uncertainty determined from the combined standard uncertainty (which include the contribution of calibration with decane) and the coverage factor k = 2.57 (for an effective degrees of freedom of 6, calculated from Welch-Satterthwaite formula, and a 0.95 level of confidence) [[20]].
Table S5 Calvet microcalorimetry results for the process of vaporization of N-ethylmorpholine.a
Ensaio / 1 / 2 / 3 / 4 / 5 / 6TCalvet / Kb / 375.72 / 375.96 / 375.85 / 375.85 / 375.85 / 375.72
m(sct) / mg / 21.4623 / 24.7950 / 25.1841 / 20.2711 / 20.6168 / 19.5893
m(rct) / mg / 21.5412 / 24.8160 / 25.2411 / 20.3145 / 20.7141 / 19.6417
m(cpd) / mg / 5.0690 / 5.0481 / 4.4696 / 5.6581 / 5.6960 / 4.9751
H(blank) / mJ / 38.652 / 31.862 / 33.357 / 37.981 / 40.579 / 39.223
H(total) / J / 2.302 / 2.370 / 2.060 / 2.619 / 2.693 / 2.282
H(corr) / J / 2.341 / 2.402 / 2.094 / 2.657 / 2.734 / 2.321
(exp)/ kJmol-1 / 53.87 / 55.51 / 54.65 / 54.79 / 55.99 / 54.43
(g)/ kJ·mol-1 / 12.41 / 12.45 / 12.43 / 12.43 / 12.43 / 12.41
(298.15 K) / kJ·mol-1 / 41.5 / 43.1 / 42.2 / 42.4 / 43.6 / 42.0
(298.15 K) = 42.42.6kJ·mol-1,c
aThe symbols presented in this table have the same meaning of the symbols of the above table.
bThe standard uncertainty of the temperature measurements is u(T/K) = 0.01.
cThe standard uncertainty corresponds to the expanded uncertainty determined from the combined standard uncertainty (which include the contribution of calibration with decane) and the coverage factor k = 2.36 (for an effective degrees of freedom of 8, calculated from Welch-Satterthwaite formula, and a 0.95 level of confidence) [20].
S4. Computational studies – G3(MP2)//B3LYP method
Molecular calculations concerned with this work were performed with the Gaussian-03 software package [[21]] using the composite method G3(MP2)//B3LYP [[22]], a variation of the Gaussian-3 (G3) theory [[23]].
Estimated gas-phase enthalpy of formation
A systematic conformation search was made for N-methylmorpholineand N-ethylmorpholine to determine the low energy conformers. The fractional population of each conformer at T = 298.15 K was calculated assuming a Boltzmann distribution.
In tables S6 and S7 are the absolute standard enthalpies, , and entropies, , obtained by G3(MP2)//B3LYP composite method [22] for the most stable conformers of each N-alkylmorpholine, and the corresponding derived gas-phase standard molar enthalpies, , entropies, , and Gibbs energy of formation, , at T = 298.15 K, and the conformational composition, i.
The gas-phase standard molar enthalpy of each working reaction was calculated taking into account eqs. S4 and S5. The enthalpy of reaction, , at T = 298.15 K, was obtained computationally from the absolute standard enthalpies, , of each species. The rearrangement of eq. S5 and the knowledge of the experimental standard molar gas-phase enthalpies of formation of all the auxiliary species used reported in table S8 enabled the calculation of the species under study.
The G3(MP2)//B3LYP absolute enthalpies, , and the experimental enthalpies of formation in the gas phase, , of the molecular species used are given in Table S8.
/ (S4)/ (S5)
S1
Table S6. Absolute standard enthalpies, , and entropies, , obtained by G3(MP2)//B3LYP composite method for the two most stable conformers of N-methylmorpholine, and the corresponding derived gas-phase standard molar enthalpies, , entropies, , and Gibbs energy of formation, , at T = 298.15 K, and the conformational composition, i. 1 a. u. (Hartree) corresponds to 2625.50 kJmol-1.
Conformationa / b /a.u. / c /
kJmol-1 / d /
JK-1mol-1 / e /
JK-1mol-1 / f /
kJmol-1 / g
I / / 326.565719 / 155.1 2.3 / 332.44 / 612.4 / 45.1 / 0.9991
II / / 326.559012 / 137.5 2.3 / 333.40 / 604.8 / 59.6 / 0.0009
aAtomcolor code: grey, C; red, O; blue, N; white, H.
bObtained from G3(MP2)//B3LYP method [22].
cEstimated from nine working reactions;
dObtained from B3LYP/6-31G(d) method for a frequency factor scale of 1.0029 [[24]] ;
eCalculated from, considering the standard absolute entropy elements values, at 298.15 K, = 130.680 JK-1mol-1, = 5.740 JK-1mol-1, = 191.609 JK-1mol-1, and = 205.147 JK-1mol-1 taken from ref. [[25]];
fCalculated from ;
g Calculated from .
Table S7. Absolute standard enthalpies, , and entropies, , obtained by G3(MP2)//B3LYP composite method for the two most stable conformers of N-ethylmorpholine, and the corresponding derived gas-phase standard molar enthalpies, , entropies, , and Gibbs energy of formation, , at T = 298.15 K, and the conformational composition, i. 1 a. u. (Hartree) corresponds to 2625.50 kJmol-1.
Conformationa / b /a.u. / c /
kJmol-1 / d /
JK-1mol-1 / e /
JK-1mol-1 / f /
kJmol-1 / g
I / / 365.802204 / 180.7 2.6 / 364.35 / 622.1 / 4.8 / 0.9231
II / / 365.799930 / 174.8 2.6 / 363.38 / 623.1 / 11.0 / 0.0760
III / / 365.795538 / 163.2 2.6 / 365.04 / 621.4 / 22.1 / 0.0009
aAtomcolor code: grey, C; red, O; blue, N; white, H.
bObtained from G3(MP2)//B3LYP method [22].
cEstimated from six working reactions;
dObtained from B3LYP/6-31G(d) method for a frequency factor scale of 1.0029 [24] ;
eCalculated from, considering the standard absolute entropy elements values, at 298.15 K, = 130.680 JK-1mol-1, = 5.740 JK-1mol-1, = 191.609 JK-1mol-1, and = 205.147 JK-1mol-1 taken from ref. [25];