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. Ribeiro da Silva

Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal

TABLE OF CONTENTSPage

S1. Purification ..................................................................................................................................................

S3

S2. Combustion calorimetry …………..…………………………………………………..…………………..

S4

S3. Vacuum drop microcalorimetric technique ……..………………………………………………………...

S8

S4. Computational studies – G3(MP2)//B3LYP method ………………………………………….………….

S11

TABLE INDEXPage

Table 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, H 298.15 K° , and entropies, S298.15 K

° , 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, ∆ f Hm

° (g), entropies, ∆ f Sm° (g),

and Gibbs energy of formation, ∆ f Gm° (g), at T = 298.15 K, and the conformational

composition, i...... S12Table S7. Absolute standard enthalpies, H 298.15 K

° , and entropies, S298.15 K° , 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, ∆ f Hm

° (g), entropies, ∆ f Sm° (g),

and Gibbs energy of formation, ∆ f Gm° (g), at T = 298.15 K, and the conformational

composition, i...... S13Table S8. G3(MP2)//B3LYP enthalpies, H 298.15 K

° , with corresponding conformer composition (in

S1

parentheses and boldface), and experimental gas-phase standard (pº = 0.1 MPa) molar enthalpies of formation, ∆ f Hm

o (g ), 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

S2

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 pressure of 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].

S3

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 m 0.530 mm i. 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 mass fraction purity

N-methylmorpholine 109-02-4 Sigma-Aldrich 0.9991 a Vacuum distillation 0.9995b

1.0001 0.0002c

N-ethylmorpholine 100-74-3 TCI 0.969 a Vacuum distillation 0.9990b

Benzoic acid 65-85-0 NIST 0.999996 a

Decane 124-18-5 Sigma-Aldrich 0.990 a a Values stated in the certificate of analysis of the supplier;b Mass fraction purities obtained from gas-liquid chromatography;c Results obtained from combustion calorimetry, based on mass fraction of carbon dioxide recovery (mean and standard deviation of the mean for six experiments).

S4

S2. Combustion calorimetry

The combustion experiments of the organic nitrogen compounds were performed with an isoperibol

calorimeter [2-4]. This calorimeter has a twin valve bomb, with an internal volume of 0.290 dm 3 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 MPa with pure oxygen (xO2≥ 0.99995). The calibration results were corrected to give the

energy equivalent, ε (calor), 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, ε (cal) = (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 (xO2≥ 0.99995) 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:

C5 H11 NO (l) + 7.25 O2 (g) → 5 CO2 (g ) + 5.5 H2 O (l) + 0.5 N2 (g) (S1)

C6 H13NO (l) + 8.75 O2 (g) → 6 CO2 (g ) + 6.5 H2 O (l) + 0.5 N2(g) (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

S5

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, ∆ U (IBP), was calculated through eq.

S3, in which ∆ T ad is the calorimeter temperature change corrected for the heat exchange and the work of

stirring, ∆ m (H2 O ) represents the difference between the mass of water added to the calorimeter and the

mass of 2900.0 g assigned to ε (cal ), ε f is the energy equivalent of the content in the final state, ∆ U (ign) is

the electric energy for the ignition, and cp (H2 O, l ) is the massic heat capacity, at constant pressure, for liquid

water.

∆ U (IBP ) /J=−{ε (cal )+∆ m (H2O ) ∙ c p (H2O, l )+εf }∆ T ad+∆ U (ign ) (S3)

After the calorimetric measurements the combustion products were analyzed: the caobon 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 ∆ c uo = (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 (∂u /∂ p)T , 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 CO2 produced 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, ∆ c uo, were calculated according to the procedure given by Hubbard et al. [15].

The results for typical combustion experiments and the individual values of ∆c uo(l), together with the

mean and the estimated standard deviation of the mean, for N-methylmorpholine and

N-ethylmorpholine are given in Tables S2 and S3, respectively.

S6

S7

Table S2 Typical 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 6

m (CO2, total) / g 1.74688 1.84867 1.47548 1.68892 1.45580 1.47456m (cpd) / g 0.68390 0.73197 0.57709 0.58663 0.56842 0.57982m (fuse) / g 0.00299 0.00213 0.00253 0.00263 0.00229 0.00287m (Melinex) / g 0.11099 0.11038 0.09427 0.17858 0.09409 0.09104m (carbon) / g 0 0 0 0.00015 0 0Tad / K 1.61767 1.71966 1.36733 1.51144 1.34849 1.36761ef / (J·K-1) 15.70 15.85 15.25 15.45 15.23 15.26m (H2O) / g 2.0 0.2 1.4 1.0 0.5 0U (IBP) / J 25194.96 26770.73 21275.73 23520.95 20993.26 24241.69U (carbon) / J 0 0 0 4.95 0 0U (Melinex) / J 2541.93 2528.00 2159.06 4089.89 2154.94 2085.04U (fuse) / J 48.56 34.59 41.09 42.71 37.19 46.61U (HNO3) / J 44.12 49.69 40.48 42.15 39.04 40.54U (ign) / J 0.68 0.74 0.73 0.78 0.74 0.65US / J 11.64 12.37 9.59 11.55 9.46 9.57

∆ c uo / (J·g-1) 32970.78 32987.80 32968.02 32967.29 32990.79 32952.36

% CO2100.083 99.958 100.029 100.007 99.987 100.005

−∆c uo = (32972.8 ± 5.8) J·g-1, b

%C O2= (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; ef, 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

S8

ignition; US, standard state correction; ∆ c uo, standard (p = 0.1 MPa) massic energy of combustion for the compound; % CO2, percentage of carbon dioxide recovered;b The standard uncertainty corresponds to the estimated standard deviation of the mean for six experiments.

S9

Table S3 Typical 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 6

m (CO2, total) / g 1.17972 0.95338 1.20530 1.21422 1.09061 1.18227m (cpd) / g 0.41191 0.31583 0.42219 0.42626 0.38297 0.42222m (fuse) / g 0.00268 0.00221 0.00200 0.00237 0.00219 0.00233m (Melinex) / g 0.10087 0.10015 0.10222 0.10178 0.09127 0.09191m (carbon) / g 0 0.00100 0 0 0 0Tad / K 1.06997 0.85399 1.09519 1.10430 0.99248 1.08065ef / (J·K-1) 14.69 14.32 14.72 14.71 14.50 14.72m (H2O) / g 1.3 1.8 0.7 1.0 0.7 0U (IBP) / J 16659.66 13285.17 17049.65 17192.85 15450.36 16820.12U (carbon) / J 0 33.00 0 0 0 0U (Melinex) / J 2310.06 2293.61 2341.13 2331.08 2090.29 2104.91U (fuse) / J 43.52 35.89 32.48 38.49 35.57 37.84U (HNO3) / J 32.90 26.73 34.29 38.77 37.68 32.90U (ign) / J 1.20 1.20 1.20 1.20 1.19 1.19US / 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

% CO299.784 99.866 99.770 99.212 99.697 99.670

−∆c uo = (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.

S10

S3. Vacuum drop-microcalorimetric technique

The standard (pº = 0.1 MPa) molar enthalpies of vaporization, ∆ lg H m

º , 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 tubes and 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 situ for 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, ∆ lg Hm

º = (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.

S11

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 6

TCalvet / 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

∆ l, 298.15Kg, T Calvet Hm

° (exp)/ kJmol-1 44.54 44.67 45.61 43.07 45.63 44.51

∆298.15 KTCalvet H m

° (g)/ kJ·mol-1 4.65 4.65 4.66 4.61 4.61 4.62

∆ lg H m

° (298.15 K) / kJ·mol-1 39.9 40.0 40.9 38.5 41.0 39.9

∆ lg H m

° (298.15 K) = 40.0 3.1 kJ·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); ∆ l, 298.15K

g, T Calvet Hm° (exp), enthalpy of vaporization from 298.15 K to temperature of the hot reaction

vessel calculated from ∆ l, 298.15Kg, T Calvet Hm

° ( exp )=¿¿, where k cal is the calibration constant of the calorimeter for

the experimental conditions and M the molar mass of the compound; ∆298.15 KTCalvet H m

° (g), enthalpy change in the

gas-phase phase from 298.15 K to the temperature of the hot reaction vessel; ∆ lg H m

° (298.15 K), enthalpy of vaporization at 298.15 K of the compound calculated from

∆ lg Hm

° ( 298.15 K ) = ∆ l ,298.15 Kg , TCalvet Hm

° (exp) ∆298.15KTCalvet H m

° (g).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].

S12

Table S5 Calvet microcalorimetry results for the process of vaporization of N-ethylmorpholine.a

Ensaio 1 2 3 4 5 6

TCalvet / 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

∆ l, 298.15Kg, T Calvet Hm

° (exp)/ kJmol-1 53.87 55.51 54.65 54.79 55.99 54.43

∆298.15 KTCalvet H m

° (g)/ kJ·mol-1 12.41 12.45 12.43 12.43 12.43 12.41

∆ lg H m

° (298.15 K) / kJ·mol-1 41.5 43.1 42.2 42.4 43.6 42.0

∆ lg H m

° (298.15 K) = 42.4 2.6 kJ·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].

S13

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-methylmorpholine and 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, H 298.15 K° , and entropies, S298.15 K

° ,

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, ∆ f Hm° (g),

entropies, ∆ f Sm° (g), and Gibbs energy of formation, ∆ f Gm

° (g), 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, ∆R H m° , at T = 298.15 K, was obtained

computationally from the absolute standard enthalpies, H 298.15 K° , 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, H 298.15 K° , and the experimental enthalpies of

formation in the gas phase, ∆ f Hm° (g), of the molecular species used are given in Table S8.

∆R H m° =∑ H298.15 K

° (products )−∑ H298.15K° ( reagents ) (S4)

∆R H m° =∑∆ f Hm

° (products )−∑∆ f Hm° (reagents ) (S5)

S14

Table S6. Absolute standard enthalpies, H 298.15 K° , and entropies, S298.15 K

° , 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, ∆ f Hm

° (g), entropies, ∆ f Sm° (g),

and Gibbs energy of formation, ∆ f Gm° (g), at T = 298.15 K, and the conformational composition, i. 1 a. u. (Hartree) corresponds to 2625.50

kJmol-1.

Conformationa H 298.15 K° b /

a.u.

∆ f Hm° (g) c /

kJmol-1

S298.15 K° d /

JK-1mol-1

∆ f Sm° (g) e /

JK-1mol-1

∆ f Gm° (g) f /

kJmol-1χ i

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

aAtom color 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, ∆ f Sm

° ( g )=S298.15 K° (conformer i )−∑ S298.15K

° (elements) considering the standard absolute entropy elements values, at 298.15 K,

S298.15 K° (H2 , g ) = 130.680 JK-1mol-1, S298.15 K

° (C, graphite ) = 5.740 JK-1mol-1, S298.15 K° (N2 , g ) = 191.609 JK-1mol-1, and S298.15 K

° (O2 , g ) = 205.147 JK-

1mol-1 taken from ref. [25];fCalculated from ∆ f Gm

° ( g )=∆f H m° ( g )−T ∆ f Sm

° ( g );

g Calculated from χ i=e

−[ Δf Gmo (g)/ RT ]

/∑i

n

e−[ Δf Gm

o ( g)/RT ]

.

S15

Table S7. Absolute standard enthalpies, H 298.15 K° , and entropies, S298.15 K

° , 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, ∆ f Hm

° (g), entropies, ∆ f Sm° (g), and

Gibbs energy of formation, ∆ f Gm° (g), at T = 298.15 K, and the conformational composition, i. 1 a. u. (Hartree) corresponds to 2625.50 kJmol-1.

Conformationa H 298.15 K° b /

a.u.

∆ f Hm° (g) c /

kJmol-1

S298.15 K° d /

JK-1mol-1

∆ f Sm° (g) e /

JK-1mol-1

∆ f Gm° (g) f /

kJmol-1χ i

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

aAtom color 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, ∆ f Sm

° ( g )=S298.15 K° (conformer i )−∑ S298.15K

° (elements) considering the standard absolute entropy elements values, at 298.15 K,

S298.15 K° (H2 , g ) = 130.680 JK-1mol-1, S298.15 K

° (C, graphite ) = 5.740 JK-1mol-1, S298.15 K° (N2 , g ) = 191.609 JK-1mol-1, and S298.15 K

° (O2 , g) = 205.147 JK-

1mol-1 taken from ref. [25];fCalculated from ∆ f Gm

° ( g )=∆f H m° ( g )−T ∆ f Sm

° ( g );

S16

g Calculated from χ i=e

−[ Δf Gmo (g)/ RT ]

/∑i

n

e−[ Δf Gm

o ( g)/RT ]

.

S17

Table S8. G3(MP2)//B3LYP enthalpies, H 298.15 K° , with corresponding conformer composition (in

parentheses and boldface), and experimental gas-phase standard (pº = 0.1 MPa) molar enthalpies of

formation, ∆ f Hmo (g ), at T = 298.15 K, for N-methylmorpholine and N-ethylmorpholine conformers

and for the auxiliary species. 1 a. u. (Hartree) corresponds to 2625.50 kJmol-1.

Atom/Compound Atom/ Molecular Structure H 298.15 K° / a. u. ∆ f Hm

o (g ) /

kJmol-1

Hydrogen H 0.499780 218.0 [25]

Carbon C 37.788425 716.7 [25]

Oxygen O 74.989704 249.17 [25]

Nitrogen N 54.524582 472.68 [25]

carbazole 516.611310 (1.0) 205.0 3.0 [26]

cyclohexane 235.407852 (1.0) 123.3 ± 0.8 [26]

9,10-dihydroanthracene 539.796179 (1.0) 159.7 2.6 [26]

N-ethylmorpholine365.802204 (0.9231)365.799930 (0.0760)365.795538 (0.0009)

This work

N-ethylpiperidine 329.906796 (0.9)329.904880 (0.1) 82.1 2.0 [27]

1-ethylpyrazole 304.326951 (1.0) 132.6 3.3 [28]

imidazole 225.873397 (1.0) 132.9 0.6 [26]

indole 363.214962 (1.0) 164.3 1.3 [29]

N-methylcarbazole 555.842444 (1.0) 199.1 0.5 [30]

(continued overleaf)

S18

Table S8 (continued) G3(MP2)//B3LYP enthalpies, H 298.15 K° , with corresponding conformer

composition (in parentheses and boldface), and experimental gas-phase standard (pº = 0.1 MPa) molar enthalpies of formation, ∆ f Hm

o (g ), at T = 298.15 K, for N-methylmorpholine and N-ethylmorpholine conformers and for the auxiliary species. 1 a. u. (Hartree) corresponds to 2625.50 kJmol-1.

Atom/Compound Atom/ Molecular Structure H 298.15 K° / a. u. ∆ f Hm

o (g ) /

kJmol-1

1-methylimidazole 265.103076 (1.0) 126.5 1.1 [31]

1-methylindole 402.445506 (1.0) 155.8 2.8 [32]

N-methylmorpholine 326.565719 (0.9991)326.559012 (0.0009) This work

N-methylphenothiazine 953.586193 (1.0) 271.3 4.1 [33]

N-methylphenoxazine 630.963683 (1.0) 97.5 1.6 [33]

N-methylpiperidine 290.670724 (1.0) 59.1 1.7 [34]

1-methylpyrazole 265.088374 (1.0) 156.5 2.1 [35]

N-methylpyrrole 249.051704 (1.0) 103.1 0.5 [26]

morpholine 287.334005 (0.78)287.332743 (0.22) 141.7 1.5 [36]

piperidine 251.439307 (0.76)251.438108 (0.24) 47.2 0.6 [26]

1H-pyrazole 225.855898 (1.0) 179.4 0.8 [37]

pyrrole 209.822541 (1.0) 108.4 0.6 [26]

tetrahydropyran 271.303681 (1.0) 223.4 1.0 [26]

thioxanthene 898.319446 (1.0) 218.7 4.2 [38]

S19

Standard molar heat capacities in the gaseous phase

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) [39].

T / KC p

o (g) / JK-1mol-1

N-methylmorpholine N-ethylmorpholine

200.00 83.87 99.49

250.00 101.48 119.98

298.15 120.05 141.70

300.00 120.78 142.56

350.00 140.96 166.16

400.00 160.96 189.52

450.00 180.05 211.80

500.00 197.85 232.56

550.00 214.27 251.70

600.00 229.32 269.24

650.00 243.11 285.31

700.00 255.75 300.05

S20

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