Adventures in Thermochemistry
James S. Chickos*
Department of Chemistry and Biochemistry
University of Missouri-St. Louis
Louis MO 63121
E-mail: jsc@umsl.edu
11
Clydesdales from the Budweiser
Brewery St. Louis MO
Applications of the The Correlation-Gas Chromatographic Method
Objectives: To go where no one else has gone
1. Evaluation of the vaporization enthalpies of large molecules
2. Application of Correlation-Gas Chromatography to a Tautomeric
Mixture - Acetylacetone
3. The Vaporization Enthalpies of Drugs and Related Substances
4. Evaluation of the Vaporization Enthalpies and Vapor Pressures of
Plasticizers
5. Identifying unusual interactions in heterocyclic systems
Diazines and Triazines
Structural Chemistry 2009, 20, 49-58
A Comparison of calculated vaporization enthalpies and normal
boiling temperatures with literature values
s-triazine
50.0±0.3
lgHm (298.15 K)/kJ.mol-1 = (0.9410.07) slngHm(358 K) - (13.10.59), (r2 = 0.9765)
a Literature
boiling temperatures from SciFinder Scholar
A Examination of the Vaporization Enthalpies and Vapor Pressures of Pyrazine, Pyrimidine, Pyridazine
and 1,3,5-Triazine. Lipkind D., Chickos J. S. Structural Chemistry 2009, 20, 49-58
N
Unknowns

N
N

N
N
N

Standards
CH3


CH3
N
N
N
N
Top, from left to right : phthalazine, benzo[c]cinnoline, quinazoline, quinoxaline.
Standards: phenazine, 2,6-dimethylquinoline, acridine, 4,7-phenanthroline, 7,8benzoquinoline,
Lipkind, D.; Chickos, J. S. Study of the Anomalous Thermochemical Behavior of 1,2-Diazines by
Correlation-Gas Chromatography J. Chem. Eng. Data 2010, 55, 698-707
Since all of the compounds studied are crystalline solids, the
following equations were used to adjust sublimation and fusion
enthalpies to T = 298.15 K and evaluate the vaporization enthalpy
Sublimation:
crgHm(298.15 K)/(kJ·mol-1)=crgHm(Tm)+[0.75+0.15Cp(cr)/(J·mol-1·K-1)][Tm/K-298.15 K]/1000
Fusion:
crlHm(298.15 K)/(kJ·mol-1)=crlHm(Tfus)+[(0.15Cp(cr)-0.26 Cp(l))/(J·mol-1·K-1)-9.83)][Tfus/K-298.15]/1000
Vaporization:
lgHm(298.15 K) = crgHm(298.15 K) - crlHm(298.15 K)
where Cp(cr), Cp(l) refer to the heat capacity of the crystal and liquid, respectively
Acree, Jr.; W.; Chickos, J. S. Phase Transition Enthalpy Measurements of Organic and
Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From
1880 to 2009, J. Phys. Chem. Ref Data 2010, 39, 1-942.
A summary of the vaporization enthalpies for diazines at T = 298 K
Vap. Enth. Calc, kJmol-1 : 58.71.4
Vap. Enth. Lit, kJmol-1 :
56.52.0
-1
Difference, kJmol :
-2.22.4
Tb/K this work/lit:
503.5/496.2
59.61.4
61.11.1
1.51.8
511.2/516.2
67.31.6
711.9
3.72.5
440/462
46.42.0
53.50.4
7.12.0
427/481
N
Vap. Enth. Calc, kJmol-1 :
Vap. Enth. Lit, kJmol-1 :
Difference, kJmol-1 :
Tb/K this work/lit:
81.90.8
89.22.3
7.32.4
638.3/633
76.70.7
78.82.2
2.12.3
606.9/na
79.7±1.3
78.4±2.0
-1.02.4
Difference in the strength of intermolecular interactions between 1,2diazines and their isomeric counterparts is approximately 6-7 kJmol-1
Lipkind, D.; Chickos, J. S. Study of the Anomalous Thermochemical Behavior of 1,2-Diazines by
Correlation-Gas Chromatography J. Chem. Eng. Data 2010, 55, 698-707
A good correlation is found between the enthalpy of transfer and the literature values for the 1,2-diazines,
Why do the 1,2-diazines behave differently from the 1,3- or 1,4-diazines?
Does the stereochemisty or the size of the ring influence the magnitude of the interaction?
N
N
N
N
N
N
Rediscovering the Wheel. Thermochemical Analysis of Energetics of the Aromatic Diazines
Verevkin, S. P.; Emel’yanenko, V. N.; Notario, R.; Roux, M.V.; Chickos, J.S.; Liebman, J. F. J. Phys.
Chem. Lett. 2012, 3, 3454.
N
N
N
N
N
2
1
N
5
N
N
3
4
N
N
N
N
N
N
6
N
N
N
N
N
CH3
Unknowns
N
N
N
N
N
CH2CH3
N
N
CH2
N
N
N
N
Ph
Standards
N
N
CH3
N
N
N
N
CH3
N
CH3
N
CH3
CH3
N
N
Unknowns:
N
N
N
N
2
1
N
N
3
4
N
N
N
N
N
N
6
5
N
N
7
N
8
N
N
11
12
N
10
N
9
N
N
13
14
N
N
Standards Set 2
Standards Set 1
N
N
N
N
N
17
16
15
N
18
N
N
N
N
N
N
19
20
21
Vaporization Enthalpies as a Function of Standards Used
gl Hm(298 K) /kJmol-1
H
N
N
N
1
N
N
3
Standards Set 1
Transpiration
Correlation
gas chromatography
N
2-(N,N-dimethylamino)pyridine (1)
55.20.10
54.62.3
0.62.3
1,5-diazabicyclo[4.3.0]non-5-ene (3)
61.90.21
61.12.4
0.82.4
4-(N,N-dimethylamino)pyridine (2)
68.40.9a
61.32.5
7.12.7
1,8-diazabicyclo[5.4.0]undec-7-ene (4)
70.70.15
67.82.6
2.92.6
imidazo[1,2-a]pyridine (6)
67.40.2
60.52.6
6.92.6
triazolo[1,5-a]pyrimidine (5)
74.2±3.8b
63.72.7
10.54.7
2
N
N
N
N
5
N
N
Standards Set 2
N
4
N
imidazo[1,2-a]pyridine (6)
67.40.23
67.14.6
0.34.6
triazolo[1,5-a]pyrimidine (5)
74.2±3.8b
70.74.5
3.55.9
4-(N,N-dimethylamino)pyridine (2)
68.40.9a
69.63.8
1.23.9
6
All the compounds whose vaporization enthalpy is in red are planar in the solid state; all are reproduced
using various pyridazines and imidazole derivatives as standards
The Vaporization Enthalpies of 2- and 4-(N,N-Dimethylamino)pyridine, 1,5-Diazabicyclo[4.3.0]non-5-ene, 1,8Diazabicyclo[5.4.0]undec-7-ene, Imidazo[1,2-a]pyridine and 1,2,4-Triazolo[1,5-a]pyrimidine by Correlation –Gas
Chromatography, Lipkind, D.; Rath, N.; Chickos, J.S. Pozdeev, V. A.; Verevkin, S. J. Phys. Chem. 2010, 55, 1628-35.
gl Hm(298 K) (kJmol-1)
Lit
CGC
Table A
Refa
gl Hm(298 K)
(kJmol-1)
(D)b
B benzene
C5H5N
pyridine
40.2±0.1
40.0±2.3
1,25
0.2±2.3
2.19 B
C 5 H7 N
N-methylpyrrole
40.6±0.8
40.3±2.5
3,26
0.3±2.6
1.96 B
C5H11N
N-methylpyrrolidine
34.2±0.7
36.6±2.4
3,27
-2.4±2.5
1.1 B
C 6 H7 N
3-methylpyridine
44.5±0.2
44.5±2.0
1,14
0 ±2.0
2.4 B
C7H10N2
2-N,N-dimethylamino-pyridine
55.2±0.1
54.6±2.3
tw
0.6±2.3
1.92 B
C8H6N2
quinoxaline
56.5±2.0
58.7±1.9
2,30
-2.2±2.8
0.51 B
C8H11N
2,4,6-trimethylpyridine
51.0±1.0
50.4±2.9
1,19
-0.6±3.0
2.26 C
C 9 H7 N
quinoline
59.3±0.2
59.5±1.3
7,18
-0.2±1.3
2.24 B
C 9 H7 N
isoquinoline
60.3±0.12
60.1±1.3
7,18
-0.2±1.3
2.53 B
C10H8N2
2-2-bipyridyl
67.02.3
63.5±3.2
7
3.5±3.9
0.69 B
C10H9N
2-methylquinoline
62.6±0.1
62.8±1.3
7,17
-0.2±1.3
2.07 B
C12H10N2
trans azobenzene
74.7±1.6
74.90.7
3,28
-0.2±1.7
0B
C13H9N
phenanthridine
80.14
79.35.5
7,29
0.8±5.5
2.39 B
C13H9N
acridine
78.63
78.2±1.3
7,29
0.4±1.3
2.29 B
Table B
C4H4N2
pyridazine
53.50.4
46.52.2
1,4
7.02.2
4.1 B
C4H6N2
N-methylimidazole
55.6±0.6
48.83.5
3,5,6
6.83.6
3.7d B
C4H6N2
N-methylpyrazole
48.0±1.3
42.8±0.2
41.6±2.9
twe,6
6.4±3.2
2.29 B
C7H10N2
4-N,N-dimethylaminopyridine
68.40.9
61.32.5
tw
7.1±2.7
4.33 B
C9H8N2
N-phenylpyrazole
70.2±3.4
63.52.9
3,25
6.7±4.5
2.0 B
C9H8N2
N-phenylimidazole
84.6±3.7
67.72.1
3,25
16.9±4.3
3.5 B
C12H8N2
benzo[c]cinnoline
89.22.3
81.91.1
2,28
7.32.5
4.1 B
Summary
Polarity seems to play a role
Extensive conjugation seems to be an important property
All compounds exhibiting enhanced intermolecular interactions are
planar
The crystal structure of 1,2,4-triazolo[1,5-a]pyrimidine suggests the
N
presence of π- π stacking in the solid state
N
N
N
5
Since most of the compounds exhibiting stronger intermolecular
interactions examined so far (pyridazines, imidazoles) seem to correlate
with each other, this suggests a common interaction responsible for the
enhanced intermolecular interactions observed; the origin of this
interaction has yet to be identified.
separation between stacks = 3.24 Å
Graduate Students
Patamaporn Umnahanant
Dmitry Lipkind
Visiting Graduate Students
Manuel Temprado, Instituto de Química Física “Rocasolano”, Madrid 28006, Spain
Visiting Faculty and Collaborators
Maria Victoria Roux, On leave from the Instituto de Química Física “Rocasolano”,
Madrid 28006, Spain
Sergey Verevkin, University of Rostock, Rostock Germany
Chatchawat Plienrasri
ott Hasty
Dmitry lipkind
Patamaporn
Umnahanant
T
F
Sergey Verevkin
Does ring size play a role?
 All compounds used as standards were six-membered ring heterocycles.
N
lgHm(298 K)
(kJmol-1)
lgHm(298 K)
(kJmol-1) [Lit]
1-methylpyrrolidine
36.62.4
34.2±0.7
1-methylpyrrole
40.32.5
40.6±0.8
4-methylpyrimidine
43.82.6
44.2
47.62.7
47.0
N
N
2,5-dimethylpyrazine
N
2,4,6-trimethylpyridine
51.42.8
51.5
quinoline
59.23.0
59.31
N
N
1-methylindole
61.13.1
62.2±1.6