Application of Correlation-Gas Chromatography to
Problems in Thermochemistry
James S. Chickos
Department of Chemistry and Biochemistry
University of Missouri-St. Louis
Louis MO 63121
E-mail: jsc@umsl.edu
October 3, 2011
Outline
• The Correlation-Gas Chromatographic Method
• Applications
1) Evaluation of the vaporization enthalpies of large
molecules, the n-alkanes, C21 to C92.
2) Evaluation of the vaporization enthalpies of tautomeric
mixtures.
3) Identifying unusual interactions in heterocyclic systems
4) Measurement of Vapor Pressure Isotope Effects
1.The Correlation-Gas Chromatographic Method
250
Signal Intensity
200
150
100
50
0
0
100
200
300
Time (sec)
400
500
A typical series of isothermal gas chromatograms as a function of
temperature; the compounds in these chromatograms are hydrocarbons
Fundamentals of Correlation –Gas Chromatography
•
tnrr: time of a non-retained reference; a measure of the time needed to travel through the
column; usually the solvent or methane
•
ta: adjusted retention time: tanalyte – tnrr; a measure of the time the analyte spends on the
column;
•
ta is inversely proportional to the vapor pressure of the analyte off the column
•
A plot of ln(to/ta) versus 1/T (K-1) results in a linear relationship with a slope equal to the
enthalpy of transfer from the column to the gas phase, -gslnHm(Tm)/R; to = 1 min
gslnHm(Tm) = lgHm(Tm) + slnHm(Tm)
•
Enthalpies of transfer values measured at Tm are found empirically to correlate linearly with
the vaporization enthalpies of standards evaluated at any temperature, including T= 298.15 K
•
Since solids do not crystallize on the column, the measurement provides the vaporization
enthalpy of the solid
Peacock, L. A.; Fuchs, R Enthalpy of Vaporization Measurements by Gas Chromatography, J. Am. Chem. Soc. 1977, 99, 5524-5.
Lipkind, D.; Chickos, J. An Examination of the Factors Influencing the Thermodynamics of Correlation Gas Chromatography as
Applied to Large Molecules and Chiral Separations, J. Chem. Eng. Data 2010, 55, 698-707.
A: Determination of Vaporization Enthalpy
• Experimental retention times for n-C14 to C20:
T/K
434.3
439.3
444.2
449.1
454.1
459
463.8
t/min
methylene
chloride
tetradecane
1.251
1.215
1.246
1.216
1.222
1.228
1.249
3.039
2.695
2.485
2.29
2.145
2.022
1.942
pentadecane
hexadecane
4.107
5.827
3.558
4.933
3.205
4.344
2.887
3.807
2.643
3.409
2.451
3.084
2.288
2.805
heptadecane
octadecane
8.329
12.283
6.907
9.994
5.939
8.403
5.097
7.065
4.47
6.071
3.959
5.265
3.54
4.624
nonadecane
eicosane
18.549
28.345
14.836
22.305
12.2
17.935
10.075
14.57
8.487
12.04
7.219
10.076
6.211
8.522
Enthalpy of Transfer Determination for
Hexadecane
• ln(to/ta) = -gslnHm(Tm)/R*1/T + intercept
• gslnHm(Tm) * 8.314 J mol-1 = 60.308 kJ mol-1
Hexadecane
0.4
ln (1/ta)
0.2
0.0
-0.2
-0.4
-0.6
0.00216 0.00218 0.00220 0.00222 0.00224 0.00226 0.00228 0.00230
1/T (K)
• Equations for the temperature dependence of
ln(to/ta) for C14 to C20 where to = 1 min:
Tm = 449 K
slngHm/R
intercept
r2
tetradecane
-6393.895
14.1610.01
0.9989
pentadecane
-6787.973
14.5970.01
0.9994
hexadecane
-7251.562
15.1900.01
0.9996
heptadecane
-7612.665
15.5870.01
0.9996
octadecane
-8014.871
16.0700.01
0.9996
nonadecane
-8457.474
16.6400.01
0.9996
eicosane
-8919.685
17.2570.01
0.9995
ln(to/ta) = -gslnHm(Tm)/R*1/T + intercept
• Vaporization enthalpies (in kJ mol-1) of the nalkanes (C14 to C20):
tetradecane
slngHm(449 K) lgHm (298.15 K) lgHm (298.15 K)
(lit)
(calc)
53.2
71.7
71.81.0
pentadecane
56.4
76.8
76.51.0
hexadecane
60.3
unknown
81.4
821.1
?
heptadecane
63.3
86.5
86.31.2
octadecane
66.6
91.4
91.11.3
nonadecane
70.3
96.4
96.41.4
eicosane
74.2
101.8
101.91.4
lgHm (298.15 K) = (1.4240.019) slngHm(Tm) – (3.980.35); r 2= 0.9991
Experimental vaporisation enthalpy, kJ /mol (T = 298.15 kJ/mol)
Correlations between vaporization enthalpy at T = 298.15 K
against the enthalpy of transfer
105
100
95
90
85
80
75
70
50
55
60
65
70
75
Enthalpies of transfer from solution to the gas phase, kJ/mol (T = Tm)
80
B: Determination of Vapor Pressures
• literature vapor pressure evaluated using the Cox equationa
• ln (p/po) = (1-Tb/T)exp(Ao +A1T +A2T 2)
Tb
Ao
103A1
106A2
tetradecane
526.691
3.13624
-2.063853
1.54151
pentadecane
543.797
3.16774
-2.062348
1.48726
hexadecane
559.978
3.18271
-2.002545
1.38448
heptadecane
575.375
3.21826
-2.04
1.38
octadecane
590.023
3.24741
-2.048039
1.36245
nonadecane
603.989
3.27626
-2.06
1.35
eicosane
617.415
3.31181
-1.02218
1.34878
705
3.41304
-1.8894
1.04575
octacosaneb
po = 101.325 kPa
aRuzicka,
K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related
Thermal data Between the Triple Point and Normal Boiling Temperatures for nAlkanes C5-C20. J. Phys. Chem. Ref. Data 1994, 23, 1-39.
• Equations for the temperature dependence of ln(to/ta) for
C14 to C20:
Tm = 449 K
slngHm/R
intercept
r2
tetradecane
-6393.895
14.1610.01
0.9989
pentadecane
-6787.973
14.5970.01
0.9994
hexadecane
-7251.562
15.1900.01
0.9996
heptadecane
-7612.665
15.5870.01
0.9996
octadecane
-8014.871
16.0700.01
0.9996
nonadecane
-8457.474
16.6400.01
0.9996
eicosane
-8919.685
17.2570.01
0.9995
ln(to/ta) = -gslnHm(Tm)/R + intercept
• Vapor pressures of n-alkanes (C14 to C20) at T = 298.15 K:
ln(to/ta) at
298.15 K
tetradecane
-7.3
ln (p/po) at
298.15 K from
Cox eq.
-10.9
ln (p/po) at
298.15 K from
correlation eq.
-10.9
pentadecane
-8.2
-12.1
-12.1
hexadecane
-9.2
unknown
-13.3
heptadecane
-10.0
-14.3
-14.3
octadecane
-10.8
-15.4
-15.4
nonadecane
-11.8
-16.6
-16.6
eicosane
-12.7
-17.8
-17.8
-13.3
?
ln(p/po) = (1.27  0.01) ln(to/ta) - (1.693  0.048); r 2 = 0.9997
po = 101.325 kPa
Correlation between ln(1/ta) calculated by extrapolation
to T = 298.15 K versus ln(p/po) calculated from the Cox
equation for C14 to C20 (po = 101.325 kPa)
-10
-11
-12
ln(p/po)
-13
-14
-15
-16
-17
-18
-19
-13
-12
-11
-10
ln(1/ta)
-9
-8
-7
ln(p/po) = (1.27  0.01) ln(to/ta) - (1.693  0.048); r 2 = 0.9997
0
-2
ln(p/po)
-4
-6
-8
-10
-12
-14
0.0018 0.0020 0.0022 0.0024 0.0026 0.0028 0.0030 0.0032 0.0034 0.0036
1/T, K-1
Vapor pressure -temperature dependence for hexadecane;
line: vapor pressure calculated from the Cox equations for C14,
circles; vapor pressures calculated by correlation treating hexadecane
as an unknown and correlating ln(to/ta) with ln(p/po) for C14, C15, C17-C20.
normal boiling temperature: 560.2 (expt); 559.9 (calcd)
Validation of the results
Compare with
(Hvap) lit
Vaporization.
Enthalpy
c-GC
Liquid
Vapor
Pressure
Compare with
(ln p/p0) lit
+ Fusion Enthalpy
Sublimation
Enthalpy (for
cryst. solids)
Compare with
(Hsub) lit
Boiling
Temperature
Compare with
(BT) lit
Some Advantages and Limitations of Correlation-Gas
Chromatography
1. The method works well on hydrocarbons and hydrocarbon
derivatives regardless of the hydrocarbon structure
2. With hydrocarbon derivatives, standards need to be chosen with the
same number and type of functional group as the compound(s) to be
evaluated unless demonstrated otherwise
3. Measurements can be made on small sample sizes and purity is not
generally an issue
4. Correlation of the standards needs to be documented experimentally
5. The correlation equations can be used to obtain vapor pressures as
well provided vapor pressures of the standards are available and to
estimate boiling temperatures.
6. The results are only as good as the quality of the standard data
• What if suitable standards for the compounds
of interest are not available?
Functional Group Contributions to Vaporization Enthalpies
Functional Group
acid
-C(=O)OH
alcohol
-OH
aldehyde
-CHO
amide [monosubst.]
-C(=O)NHamine [pri.] -NH2
amine [sec.] -NHamine [tert.] >Nbromide
-Br
chloride
-Cl
ester
-C(=O)Oether
>O
Group Value
b
38.8
29.4
12.9
42.5
14.8
8.9
6.6
14.4
10.8
10.5
5.0
Functional Group
iodide
-I
ketone
>C=O
nitrile
-CN
nitro
-NO2
heterocyclic aromatic
nitrogen
=Nsulfide
>S
disulfide
-SSsulfoxide
>SO
sulfone
-SO2thiolester
-C(=O)Sthiol
-SH
Group Value
b
18.0
10.5
16.7
22.8
[12.2]
13.4
[22.3]
[42.4]
[53.0]
[16.9]
13.9
lgHm(298.15 K)/(kJ.mol-1) = 4.69.(n-nQ) + (1.3).nQ + b + (3.0)
n = number of non-quaternary carbons; nQ = number of quaternary carbons; values in
brackets are tentative assignments
Chickos, J. S.; Acree, Jr. W. Liebman, J. F. (Frurip, D.; Irikura, K., Editors) Computational Thermochem.,
Prediction and Estimation of Molecular Thermodynamics, ACS: Washington DC, 1998, pp 63-93
Applications
• The evaluation of vaporization enthalp[ies
of large molecules
1. Applications of correlation gas chromatography for the
evaluation of the vaporization enthalpies of large molecules,
the n-alkanes, C21 to C92.
9000
8000
Intensity
7000
C60
6000
5000
4000
3000
10
20
30
Time / min
A partial GC trace of a mixture of Polywax 1000 spiked with nalkanes C42, C50 and C60 run at T = 648 K
Applications of correlation gas chromatography for the evaluation of the vaporization
enthalpies of large molecules, the n-alkanes, C21 to C92.
• Reliable vaporization enthalpies and vapor pressures are available up to eicosane
• Using the available data from heptadecane to eicosane, vaporization enthalpies
were evaluated for C21,C22, C23. These values in turn were used to evaluate the
larger n-alkanes in a stepwise process up to C38, most of which are commercially
available.
• Additionally, a few other larger n-alkanes, C40, C42, C48, C50, and C60 are likewise
commercially available. These were used in conjunction with polywax to evaluate
vaporization enthalpies and vapor pressures up to C92 (even series)
• Since very little experimental data was available for comparison, the results from
correlation gas chromatography were compared with estimations by PERT2a and
estimated Antoine Constantsb
aPERT2
is a FORTRAN program written by D.L. Morgan in 1996 which includes parameters for n-alkanes
from C1 to C100 and heat of vaporization and vapor pressure correlations. Morgan, D. L.; Kobayashi, R.
“Extension of Pitzer CSP models for vapor pressures and heats of vaporization to long chain hydrocarbons,”
Fluid Phase Equilibrium 1994, 94, 51-87.
bKudchadker, A.
P.; Zwolinski, B. J. “Vapor Pressures and Boiling Points of Normal Alkanes, C 21 to C100,” J.
Chem. Eng. Data 1966, 11, 253-55.
400
300
200
g
l Hm (298.15 K) / kJ mol
-1
500
curvature
100
0
0
20
40
60
80
100
N
The vaporization enthalpies at T = 298.15 for C5 to C92. N represents the
number of carbon atoms. The solid line was derived using the recommended
vaporization enthalpies of C5 to C20 The empty circles are values calculated
values using the program PERT2 The solid circles are values evaluated from
correlations of slngHm(Tm) with lgHm(298.15K).
Vapor pressures and Vaporization Enthalpies of the n Alkanes from C78 to C92 at T = 298.15 K by
Correlation–Gas Chromatography, Chickos, J. S.; Lipkind, D. J. Chem.Eng. Data 2008, 53, 2432–2440.
The Vaporization Enthalpies of the n-Alkanes at T = 298.15 K As A Function
of the Number of Carbon Atoms, N
N
lgHm(298.15 K)
kJ mol-1
N
lgHm(298.15 K)
kJ mol-1
N
lgHm(298.15 K)
kJ mol-1
N
lgHm(298.15 K)
kJ mol-1
5
26.42
21
106.8±2.6
36
182.8±5.5
64
315.4±2.9
6
31.52
22
111.9±2.7
37
187.5±5.6
66
324.0±3.0
7
36.57
23
117.0±2.8
38
192.5±5.7 b
68
331.9±3.0
8
41.56
24
121.9±2.8
40
203.5±2.9
70
340.3±3.1
9
46.55
25
126.8±2.9
42
213.5±2.1
72
348.4±3.2
10
51.42
26
131.7±3.3
44
223.7±2.3
74
356.2±3.3
11
56.58
27
135.6±3.3
46
233.3±2.3
76
364.3±3.3
12
61.52
28
141.9±5.1
48
243.0±2.4
78
372.1±1.4
13
66.68
29
147.1±5.3
50
252.5±2.5
80
379.6±2.2
14
71.73
30
152.3±5.3
52
261.8±3.6
82
387.2±2.4
15
76.77
31
157.2±1.4 b
54
271.0±3.7
84
394.0±3.2
16
81.35
32
162.5±1.4
56
279.7±3.8
86
402.2±2.6
17
86.47
33
167.6±1.4
58
288.5±3.9
88
409.3±3.9
18
91.44
34
172.7±1.5
60
299.9±3.0
90
416.5±4.3
19
96.44
35
178.1±5.4 b
62
306.8±2.8
92
424.5±4.5
How is it possible to measure a vaporization enthalpy greater
that a C-C bond strength (~335 kJmol-1)?
Vapor pressures and vaporization enthalpies for C14 to C20 are known over a large
temperature range. glHm(Tm) and ΔslngHm(Tm) correlate at any temperature
Values of at ΔslngHm(449 K) and ΔlgHm(449 K) on an SPB-5 Column
Tm = 449 K
-slope/T
intercept
ΔslngHm(449 K)
kJmol-1
ΔlgHm(449 K)
kJmol-1
lit1
tetradecane
pentadecane
hexadecane
heptadecane
octadecane
nonadecane
eicosane
6393.8±95
6787.9±73
7251.5±62
7612.6±65
8014.8±71
8457.4±74
8919.6±85
14.161±0.01
14.597±0.01
15.190±0.01
15.587±0.01
16.070±0.01
16.640±0.01
17.257±0.01
53.2±0.8
56.4±0.6
60.3±0.5
63.3±0.5
66.6±0.6
70.3±0.6
74.2±0.7
56.92
60.71
64.50
68.19
72.11
76.01
79.81
glHm(449 K)/kJmol-1 = (1.0980.0133) slngHm(449 K) - (1.390.25)
calcd (eq 1)
57.0±0.8
60.6±0.8
64.8±0.9
68.1±0.9
71.8±1.0
75.8±1.0
80.1±1.1
r2 = 0.9993
(1)
slngHm(Tm) = lgHm(Tm) + slnHm(Tm)
slnHm(Tm) must be of opposite sign to lgHm(Tm)
1Ruzicka,
K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related Thermal
data Between the Triple Point and Normal Boiling Temperatures for n-Alkanes C5-C20. J.
Phys. Chem. Ref. Data 1994, 23, 1-39.
Values of at ΔslngHm(509K) and ΔlgHm(509 K) on an SPB-5 Column
-slope T
intercept
ΔslngHm(509 K)
kJ⋅mol-1
heptadecane
octadecane
nonadecane
eicosane
heneicosane
docosane
tricosane
6108.2±78.2
6489.9±63.8
6901.0±58.7
7270.0±60.5
7670.9±65.3
8064.5±71.6
8451.1±73.9
12.148±0.008
12.584±0.006
13.077±0.006
13.496±0.006
13.974±0.006
14.439±0.007
14.897±0.008
50.8±0.7
54.0±0.5
57.4±0.5
60.4±0.5
63.8±0.5
67.1±0.6
70.3±0.7
ΔlgHm(509 K)
kJ⋅mol-1
lit1,2
calcd
62.831
66.341
69.741
73.071
76.662
80.132
83.542
lgHm(509 K)/kJmol-1 = (1.0620.004) slngHm(509 K) + (8.94.020.07)
62.9±0.3
66.2±0.3
69.8±0.3
73.1±0.3
76.6±0.3
80.1±0.4
83.5±0.4
r2 = 0.9999
1Ruzicka,
K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related Thermal data Between the
Triple Point and Normal Boiling Temperatures for n-Alkanes C5-C20. J. Phys. Chem. Ref. Data 1994, 23, 139.
2Chickos,
J. S.; Hanshaw, W. Vapor pressures and vaporization enthalpies of the n-alkanes from C21-C30 at
T = 298.15 K by correlation–gas chromatography, J. Chem. Eng Data 2004, 49, 77-85.
Enthalpies of Condensation: -slngHm(T), - lgHm(T) and slnHm(T) as a Function of
Temperature
-ΔslngHm(449 K)
tetradecane
pentadecane
hexadecane
heptadecane
octadecane
nonadecane
eicosane
-53.2±0.8
-56.4±0.6
-60.3±0.5
-63.3±0.5
-66.6±0.6
-70.3±0.6
-74.2±0.7
-ΔslngHm(509 K)
heptadecane
octadecane
nonadecane
eicosane
heneicosane
docosane
tricosane
-50.8±0.7
-54.0±0.5
-57.4±0.5
-60.4±0.5
-63.8±0.5
-67.1±0.6
-70.3±0.7
-ΔlgHm(449 K) (lit)
kJ⋅mol-1
-56.92
-60.71
-64.5
-68.19
-72.11
-76.01
-79.81
-ΔlgHm(509 K) (lit)
kJ⋅mol-1
-62.83
-66.34
-69.82
-73.07
-76.66
-80.13
-83.54
ΔslnHm(449 K)
3.7±0.8
4.3±0.6
4.2±0.5
4.9±0.5
5.5±0.6
5.7±0.6
5.6±0.7
ΔslnHm(509 K)
12.0±0.7
12.3±0.5
12.4±0.5
12.7±0.5
12.9±0.5
13.0±0.6
13.2±0.7
gslnHm(Tm) = lgHm(Tm) + slnHm(Tm)
18
16
slnHm(Tm) / kJ mol
-1
14
12
10
8
6
4
2
0
300
350
400
450
500
550
600
T/K
Figure. The effect of temperature, 450, 509, 539 K, on the magnitude of
slnHm(T/ K). ■, eicosane; ●, nonadecane.
Conclusions:
1. The enthalpy of interaction of analyte with the column is
endothermic and a function of temperature; this allows access
to the measurement of large vaporization enthalpies
2. This may also help focus GC peaks and oppose diffusion
broadening
3. The overall enthalpy of condensation on the column is still
highly exothermic, just less so then might have been imagined
2. An Application of Correlation-Gas Chromatography to a
Tautomeric Mixture
H
O
O
O
O
C
CH 3
CH 2
CH 3
CH 3
CH
CH 3
0.186
0.814
The enthalpy of formation of the equilibrium mixture of the pure liquid,
(-425.5±1.0)kJ·mol-1, has been reported by Hacking and Pilcher.
Acetylacetone forms a number of metal complexes whose enthalpies of
formation have been used to determine metal oxygen bond strengths.
•Hacking, J.M.; Pilcher, G. J. Chem. Thermodyn. 1979, 11, 1015-1017. Irving,
R.J.; Wadso, I. Acta Chem.Scand. 1970, 24, 589-592
Table. Summary of all enthalpy differences between 2,4-pentanedione and
(Z)-4-hydroxy-3-penten-2-one in the liquid and gas phase available to
Hacking and Pilcher, and Irving and Wadso. Enthalpy differences
measured by the temperature dependence of the equilibrium constant.
m)liq
Hdiketo/enol(T
–1
kJ mol
–11.9±0.8
Tm/K Hdiketo/enol(Tm)gas
–1
kJ mol
Tm/K
Method
Year
–18.0
388
UV
1977
–7.5±1.5
373
Photoelectron
Spectroscopy
1974
NMR
1966
306
–16.3
1959
–11.3±0.4
NMR
1957
–7.8
273
Bromination
1952
–10.0±0.8
386
IR
1951
Vaporization Enthalpy of the Pure Enol at T = 298.15 K
∆Hk/e = +0.67 kJ mol-1
C5H8O2(gas, 93.3%enol)
C5H8O2(gas, 100%enol)
∆lgHm(298.15K) = (41.8 ± 0.2) kJmol-1
measured calorimetrically
C5H8O2(liquid, 81.4%enol)
∆lgHm(298.15K) = (43.2 ± 0.2) kJ mol-1
C5H8O2(liquid, 100%enol)
∆Hk/e = -2.1 kJ mol-1
•A trace of concentrated sulfuric acid was used by Irving and Wadso to
rapidly equilibrate the diketo and enol forms. Since the enol is more volatile,
it was assumed that tautomerization of the diketo form to the enol
contributed –2.1 kJ mol-1during vaporization.. It was also assumed that the
composition in the gas phase was the equilibrium concentration.
∆lgHm(298.15K) = (41.8 ± 0.2) –( -2.1 - 0.67) = (43.2 ± 0.2) kJmol-1
gas, 100%
diketo
(–374.4  1.3)
diketo/enolHm(g)=(–10.0  0.8)
gas,100% enol
(–384.4  1.3)
fHm(298.15
K) / kJ mol–1
lgHm(298.15K) = (43.2  0.2)
liquid,100%
diketo
(–416.3  1.1)
diketo/enolHm(l)=(–11.3  0.4)
liquid,
81.4% enol
18.6% diketo
(-425.5  1.0)
(–427.6  1.1)
liquid,100% enol
0
0.814
1
x(enol)
The thermochemical scheme to calculate the enthalpy of formation of (Z)-4-hydroxy-3pentene-2-one and 2,4-pentanedione scheme used by Hacking and Pilcher in 1979
The enthalpy difference of the two tautomers in the
gas phase was measured by infrared spectroscopy in
1951
Gas Phase FT-IR spectrum of 2,4-pentanedione, Aldrich Chemical Co.
The enthalpy difference of the two tautomers in the gas phase was remeasured by gas phase 1H NMR spectroscopy in 1985.
5.3 ppm enol vinyl 1H
3.3 ppm keto methylene
1H
Folkendt, M.M.J.et.al.
Phys. Chem. 1985, 89,
3347-3352
1.9 ppm enol methyl 1H
2.0 ppm keto methyl 1H
Table. A summary of all the enthalpy differences measured between 2,4-pentanedione and
(Z)-4-hydroxy-3-penten-2-one in the liquid and gas phase. Enthalpy differences measured by
the temperature dependence of the equilibrium constant.
m)liq
Hdiketo/enol(T
–1
kJ mol
Tm/K
–11.7
303
Hdiketo/enol(T–1m)gas
kJ mol
Tm/K
Method
Year
NMR
1996
-
–17.0
422
Photoelectron
Spectroscopy
1987
–11.8
394.5
–19.5
409
NMR
1985
–11.7±1.3
311
NMR
1982
–11.9±0.8
–18.0
388
UV
1977
–7.5±1.5
373
Photoelectron
Spectroscopy
1974
NMR
1966
306
–16.3
1959
–11.3
NMR
1957
–7.8
273
Bromination
1952
–10.0±0.8
386
IR
1951
The gas phase and condensed phase enthalpies are different, suggesting tautomer interaction
H
O
O
O
O
C
CH 3
CH 2
CH 3
CH 3
CH
CH 3
If the pure enol form( 0.814 mol) is mixed with the pure keto form (0.186 mol)
at the equilibrium concentrations, will ∆H = 0 ?
Is ∆Hmix = 0 ?
If ∆Hmix ≠ 0
If the solution heats up when the pure diketo and enol are mixed at their
equilibrium concentration, it will take more energy to vaporize the two liquids
as a mixture at T= 298.15 K ;
• If the solution cools down, it will take less heat to vaporize the two liquids as a
mixture at T = 298.15 K.
• Since Hdiketo/enol(liq) ≠ Hdiketo/enol(gas),we decided to measure lgHm(298.15K)
Intensity / arbitrary units
Correlation Gas Chromatography: an ideal method for
determining the vaporization enthalpy of a pure material even
though the material of interest may be present in the mixture
provided all components can be separated
0
50
100
150
200
Time / s
Gas Chromatograph of acetylacetone
250
300
Table. Enthalpy of transfer and vaporization enthalpy obtained for (Z)-4-hydroxy-3penten-2-one.
Compound
∆slngHm(387 K) ∆lgHm(298.15 K) ∆lgHm(298.15 K)
/kJ mol-1
/kJ mol-1(lit) /kJ mol-1(calcd)
27.92
48.7
48.7
Slope
Intercept
-3358.8
10.092
(Z)-4-hydroxy-3-penten-2- -3703.9
one
ethyl 2-hydroxypropanoate -3942.7
10.520
30.79
10.977
32.78
52.5
52.3
4-hydroxy-4-methyl-2pentanone
ethyl 3-hydroxybutanoate
-3998.0
10.914
33.24
52.3
52.6
-4516.7
11.712
37.55
55.9
55.8
ethyl 3-hydroxyhexanoate
-5476.8
13.020
45.53
61.9
61.6
o-hydroxyacetophenone
-5213.3
12.053
43.34
59.6
60.0
3-hydroxybutanone
50.8±0.6
lgHm(298.15 K)/kJ mol–1 = (0.734±0.021) slngHm(359 K) + (28.21±0.32) r2 = 0.997
Table. Enthalpy of Transfer and Vaporization Enthalpies obtained for 2,4pentanedione
Compound
∆slngHm(328 K) ∆lgH (298.15 K) ∆lgHm(298.15K)
/kJ mol-1
/kJ mol-1(lit) /kJ mol-1(calcd)
Slope
Intercept
2,3-butanedione
-3153.8
1.493
26.22
2,4-pentanedione
-4305.8
12.034
35.80
2,2,4,4-tetramethylcyclobutanedione
-4603.4
12.285
38.27
54.2
54.3
benzoquinone
-4614.4
12.111
38.36
53.4
54.4
2,5-hexanedione
-4800.5
12.592
39.91
57.5
56.4
39.0
38.9
51.2±2.2
lgHm(298.15 K)/kJ mol–1 = (1.283±0.1) slngHm(328 K) + (5.21±1.1)
r2 = 0.989
(Z)-4-hydroxy-3-penten-2-one
∆lgHm(298.15K)/kJ.mol-1(corr- gas chromatography)=(50.8±0.6) kJ mol-1
∆lgHm(298.15K)/kJ mol-1(measured as a mixture) = (43.2 0.2) kJ.mol–1a
a Measured as a mixture but calculated for the pure material
∆Hmix = (50.8±0.6) - (43.2 ±0.2) =
7.6±0.6 kJ.mol-1
∆Hketo-enol tautomerism observed = ∆Hketo-enol tautomerism real +∆Hmix
∆Hketo-enol tautomerism real = (-11.3)-(+7.6±0.6) = -18.9±0.6 kJ mol-1
Since the vaporization enthalpy at T = 298.15 K is approximately the
same for 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one, the
difference in the gas phase between the two tautomers is also ~ -18.9 kJ
mol-1
The enthalpies of formation of the tautomers of acetylacetone in the liquid phase
and in the gas phase
gas, diketo
(–358.9±2.5) kJ mol-1
∆diketo/enol Hm(g) = (-19.3±2.8) kJ mol-1
(-19.5)kJ mol-1 Folkendt,M. et al.
gas, 100% enol
(–378.2±1.2) kJ mol-1
ΔlgHm=(51.2±2.2) kJ mol-1
lgHm= (50.8±0.6) kJ mol-1
liquid, diketo
(–410.1±1.2) kJ mol-1
∆diketo/enol Hm(l)= -18.9 kJ mol-1
(–429.0±1.0)kJ mol-1
liquid, 100% enol
0
0.814
x(enol)
1
Table. Summary of Standard Molar Enthalpies at T = 298.15 K of the Two
Acetylacetone Tautomers
Compound
fHºm(l) / kJ mol–1
 lgHm / kJ mol–1
fHºm(g) / kJ mol–1
2,4-pentanedione
–410.1  1.2
[–416.3  1.1]
51.2  2.2
–358.9  2.5
[–374.4  1.3]
Z 4-hydroxy-3penten-2-one
–429.0  1.0
[–427.6  1.1]
50.8  0.6
[43.2  0.1]
–378.2  1.2
[–384.4  1.3]
∆fHm (T = 298.15 K, liquid, 81.4% enol and 18.6% diketo) = -425.5±1.0 kJ mol-1.
values in the brackets are the previous accepted values.
Temprado, M.; Roux, M. V.; Umnahanant, P.; Zhao, H.; Chickos, J. S. J. Phys. Chem. B.
2005; 109, 12590-12595.
Application 3: Identifying unusual interactions in heterocyclic systems
1,2-Diazines
Unknowns:
• s-triazine
N
N
N
N
N
• Pyrimidines
H3C
N
N
4-methylpyrimidine
• Pyridazines
N
N
N
N
H3C
3-methylpyridazine
Standards:
N
• Pyrazines
N
• Pyridines
N
N
N
2-methylpyrazine
N
H3C
2,5-dimethylpyrazine
H3C
N
CH3
N
CH3
N
CH3
H3C
N
CH3
CH3
CH3
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 = 0.9865)
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 :
Vap. Enth. Lit, kJmol-1 :
Difference, kJmol-1 :
58.71.4
56.52.0
-2.22.4
59.61.4
61.11.1
1.51.8
67.31.6
711.9
3.72.5
46.42.0
53.50.4
7.12.0
N
Vap. Enth. Calc, kJmol-1 :
Vap. Enth. Lit, kJmol-1 :
Difference, kJmol-1 :
81.90.8
89.22.3
7.32.4
76.70.7
78.82.2
2.12.3
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 1,2Diazines by Correlation-Gas Chromatography J. Chem. Eng. Data 2010, 55, 698-707
Vaporization Enthalpies Using Pyridine Derivatives
as Standards
lgHm
lgHm
(298 K)
(298 K)
(kJmol-1) (kJmol-1) [Lit]
1-EthylIMI
N
lgHm
(298 K)
(kJmol-1)
1-MeIMI
48.62.2
55.6±1.3
6.83.6
1-EtIMI
51.42.3
66.0±3.9
14.63.7
1-Phpyrazole
63.52.0
70.2±3.4
6.7±3.9
1-BzIMI
72.33.8
83.0±1.0
10.8±3.9
Ph
N
What structural factors influence this behavior ?
A Study of the Vaporization Enthalpies of Some 1-Substituted Imidazoles and Pyrazoles by Correlation-Gas
Chromatography, Lipkind, D.; Plienrasri, C. Chickos, J. S. J. Phys. Chem. B 2010, 114, 16959–16967
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
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.
4) Measurement of Vapor Pressure Isotope Effects
Typical GC Plot of Deuterated and Undeuterated Hydrocarbons
80000
n-C7H16; n-C7D16
CH3C6H5; CD3C6D5
Intensity
60000
n-C8H18; n-C8D18
40000
p-CH3C6H4CH3
20000
o-CH3C6H4CH3
0
2
4
6
8
10
12
14
16
t/min
A typical gas chromatogram of a series of labeled/unlabeled
hydrocarbons run on an RTX-1 column at T = 300 K; in order of
elution, heptane-d16/heptane, toluene-d8/toluene, octane-d18/octane,
p-xylene-d10/p-xylene, o-xylene-d10/o-xylene. The small peak with
the shortest retention time is methane.
Table. Deuterium Isotope Effects on Vaporization Enthalpy
slope intercept slngHm(293 K) lgHm(298)/kJ.mol-1
kJ.mol-1
lit
calc
hexane-d14
-3439.9
hexane
-3472.3
cyclohexane-d12-3576.4
cyclohexane -3601.7
heptane-d16
-4018.6
heptane
-4058.5
toluene-d8
-4209.2
toluene
-4215.1
10.286
10.308
10.111
10.127
11.215
11.252
11.184
11.169
28.60
28.87
29.73
29.94
33.41
33.74
34.99
35.04
31.52
33.12
36.57
37.99
31.47±1.6
31.74±1.6
32.61±1.7
32.83±1.7
36.32±1.9
36.66±1.9
37.92±2.0
37.97±2.0
lgHm (298.15 K)/kJ.mol-1=(1.0090.056)slngHm(293 K) + (2.6150.27), (r2 =
0.9946)
Measurement of Vapor Pressure Isotope Effects
A/T 3
hexane-d14
heptane-d16
p-xylene-d10
o-xylene-d10
toluene-d8
-17917619
-5444070
-71657137
-89591864
-42775261
BT 2
-45199
-218518
282831
419760
88847
C/T 1
-2909.62
-2758.60
-4622.31
-5088.30
-3696.58
D
9.429
9.220
10.628
11.06
9.806
Tb/K(calc)
339.3
368
410.1
415.7
383.1
Tb/K(exp)
pH/pD
341.9
371.4
411.5
417.6
383.8
298.15 K
0.909
0.892
0.945
0.937
0.926
ln(p/po) = A(T/K)-3 + B(T/K)-2 + C(T/K)-1 + D
Zhao, H.; Unhannanant, P.; Hanshaw, W. Chickos, J. S. The Enthalpies of Vaporization and
Vapor Pressures of Some Deuterated Hydrocarbons. Liquid Vapor Pressure Isotope Effects
J. Chem. Eng. Data 2008, 53, 1545–1556.
Graduate Students
William Hanshaw
Patamaporn Umnahanant
Hui Zhao
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
From Left to right: Bill Hanshaw, Maria Victoria Roux, Jim Chickos,
Patanaporn Unmahanant (T), Richard Heinz, and Hui Zhao
From left to right: Rachel Maxwell, her friend, Richard Heinz, Jim
Chickos, Dmitry Lipkind, and Darrell Hasty
separation between stacks = 3.24 Å
Does a 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