Thermodynamic properties, conformational composition, and phase transitions of cyclopentanol

Article abstract of DOI:10.1006/jcht.1995.0101

Thermodynamic properties of cyclopentanol were studied.The molar heat capacity of c-C5H9OH(cr and l) in the temperature range T = 5.4 K to 303.0 K was measured by vacuum adiabatic calorimetry.Three solid-to-solid transitions were found: at T = 176 K with Δ_trsH_m = (57 +/- 5) J*mol^-1; at T = 202.6 K with Δ_trsH_m = (3366 +/- 14) J*mol^-1, and at T = 234 K with Δ_trsH_m = (55 +/- 6) J*mol^-1.The fusion temperature of c-C5H9OH is 255.6 K, and Δ_fusH_m = (1227 +/- 5) J*mol^-1.Basic thermodynamic functions at T = 298.15 K in the liquid state are C_s,m = (182.48 +/- 0.73) J*K^-1*mol^-1, S_m = (204.14 +/- 0.90) J*K^-1*mol^-1, and Φ_m = (96.98 +/- 0.40) J*K^-1*mol^-1.The enthalpy of vaporization was measured with a heat-conducting microcalorimeter: Δ_vapH_m(298.15 K) = (57.05 +/- 0.65) kJ*mol^-1.Using these and literature data, the standard molar entropy of c-C5H9OH(g) was determined: S⁰_m(g, 340 K) = (362.9 +/- 2.4) J*K^-1*mol^-1.Conformational analysis was made by the molecular-mechanics method, and statistical calculations of standard molar thermodynamic functions in the ideal-gas state were carried out on the basis of molecular parameters and conformational properties.The calculated entropy value at T = 340 K was put into agreement with the experimental one by adjusting the pseudorotational moment of inertia.The standard molar entropy and molar heat capacity of c-C5H9OH in the ideal-gas state at T = 298.15 K are 347.91 J*K^-1*mol^-1 and 105.43 J*K^-1*mol^-1, respectively.Thermodynamic analysis of phase transitions in the condensed state was made.It was shown that pseudorotation in the plastic crystal state of c-C5H9OH is significantly hindered.Thermodynamic quantities allowed us to propose the absence of a non-equilibrium mixture of conformers at T -> 0.An anomalously low entropy difference between liquid and rigid crystal of cyclopentanol in comparison with other cyclopentane derivatives shows a relatively high ordering in the liquid.

Full text of DOI:10.1006/jcht.1995.0101

M-3133
J. Chem. Thermodynamics 1995, 27, 953–967
Thermodynamic properties, conformational
composition, and phase transitions of cyclopentanol
G. J. Kabo, V. V. Diky, A. A. Kozyro, A. P. Krasulin,
and V. M. Sevruk
Belarussian State University, Leningradskaya 14, Minsk 220080,
Republic of Belarus
(Received 28 February 1995)
Thermodynamic properties of cyclopentanol were studied. The molar heat capacity
of c-C5H9OH(cr and l) in the temperature range T = 5.4 K to 303.0 K was measured by
vacuum adiabatic calorimetry. Three solid-to-solid transitions were found: at T = 176 K
with DtrsHm = (57 2 5) J·mol−1; at T = 202.6 K with DtrsHm = (3366 2 14) J·mol−1, and at
T=234 K with DtrsHm=(5526) J·mol−1. The fusion temperature of c-C5H9OH is 255.6 K,
and
D
fusHm=(122725) J·mol−1
. Basic thermodynamic functions at T=298.15 K in the
liquid state are Cs, m = (182.48 2 0.73) J·K−1·mol−1, Sm = (204.14 2 0.90) J·K−1·mol−1, and
Fm = (96.98 2 0.40) J·K−1·mol−1
.
The enthalpy of vaporization was measured with a
heat-conducting microcalorimeter: DvapHm(298.15 K)=(57.0520.65) kJ·mol−1. Using these and
literature data, the standard molar entropy of c-C5H9OH(g) was determined:
Sm°(g, 340 K) = (362.9 2 2.4) J·K−1·mol−1
. Conformational analysis was made by the
molecular-mechanics method, and statistical calculations of standard molar thermodynamic
functions in the ideal-gas state were carried out on the basis of molecular parameters
and conformational properties. The calculated entropy value at T=340 K was put into agreement
with the experimental one by adjusting the pseudorotational moment of inertia. The standard
molar entropy and molar heat capacity of c-C5H9OH in the ideal-gas
state at T = 298.15 K are 347.91 J·K−1·mol−1 and 105.43 J·K−1·mol−1
, respectively.
Thermodynamic analysis of phase transitions in the condensed state was made. It was shown that
pseudorotation in the plastic crystal state of c-C5H9OH is significantly hindered. Thermodynamic
quantities allowed us to propose the absence of a non-equilibrium mixture of conformers at T:0.
An anomalously low entropy difference between liquid and rigid crystal of cyclopentanol in
comparison with other cyclopentane derivatives shows a relatively high ordering in the liquid.
7 1995 Academic Press Limited
1. Introduction
This work continues our study of the influence of pseudorotation (ring inversion in
compounds containing five-membered cycles) on polymorphism in the crystal state and
on the possibility to form plastic crystals. In contrast to chlorocyclopentane, studied
earlier,(1) cyclopentanol possesses an additional degree of freedom caused by internal
rotation of the OH– top with a rather low potential barrier, and it also possesses an
ability to form H-bonds. The number of solid-to-solid transitions, observed earlier for
cyclopentanol is significantly higher than that for chlorocyclopentane. Parks et al.(2)
0021–9614/95/090953+15 $12.00/0
7 1995 Academic Press Limited

954
G. J. Kabo et al.
TABLE 1. Thermodynamic characteristics of phase transitions of c-C5H9OH in the condensed state
Phase
transition
Ttrs
K
DtrsHm
DtrsSm
Reference
kJ·mol−1
J·K−1·mol−1
cr, IV:cr, III
cr, III:cr, II
162
176
0.0685
0.057
0.42
0.324
2
this work
202.8
195
201
3.708
3.9
18.28
20.0
2
4
6
202.6
3.366
16.61
this work
cr, II:cr, I
cr, I:liquid
237
236.4
234
0.108
0.15
0.055
0.46
0.64
0.235
2
4
this work
257.4
255.7
253.6
255.6
1.535
1.67
1.6
6.47
6.53
6.31
4.80
2
4
6
1.227
this work
found three such transitions at the temperatures T=(162, 202.8, and 237) K studying
the heat capacity of cyclopentanol in the temperature range from 80 K to 300 K
(table 1). One of these transitions occurring at
T
=
202.8 K with
DtrsHm = 3.708 kJ·mol−1 probably corresponds to transformation into the
plastic-crystal state. Polymorphism of crystalline cyclopentanol has been studied
later by d.s.c.(3–6) Besides, influence of pressure on solid-to-solid transitions was
studied,(4) X-ray studies of crystals I and II were made,(7) dielectric properties of
cyclopentanol in different phases including metastable ones were measured,(8, 9) spectral
investigations of crystals were made, and the conformational composition was
determined.(10–12)
A comprehensive study of the thermodynamic properties of cyclopentanol in
different states of aggregation and an analysis of some thermodynamic aspects
of polymorphism in the crystalline state are made in this work.
2. Experimental
Cyclopentanol was synthesized from cyclopentanone by hydrogenation with NaBH4
in a mixture of methanol and propan-2-ol (volume proportion: 3 to 7) under cooling
with ice. The sample was washed with NaHSO3(aq) and extracted with diethyl ether,
dried with Na2SO4, and distilled on a column packed with glass helices (about
20 theoretical plates) at the pressure p=40 kPa and T=353 K. Finally the sample was
dried in a vacuum desiccator over P2O5. The mole fraction of c-C5H9OH in the sample
was 0.998 according to g.l.c.
Measurements of heat capacity were made with an automatic adiabatic calorimeter
TAU-1, fabricated by VNIIFTRI (Moscow). The uncertainty of determination of Cs is
up to 0.02·Cs at TQ10 K, 0.01·Cs in the range T=10 K to 20 K, and is no more than
0.004·Cs at Tq40 K. The sample (mass: 0.58692 g) was placed in a container of
stainless steel. The container was a sliding fit into a copper sleeve, supplied with a

Properties of cyclopentanol
955
manganin heater. An (iron+rhodium) resistance thermometer (R0=50 V) fabricated
and calibrated by VNIIFTRI was used for temperature measurements.
Adiabatic conditions in the calorimeter were maintained automatically in
proportional-integral-differential mode. A 4-junction differential thermocouple was
used as a sensor for this purpose.
Enthalpy of vaporization was measured with a heat-conducting differential
microcalorimeter MID-200 improved in our Laboratory and described earlier.(13)
Weighings of samples were adjusted to vacuum during analysis of the experimental
results. Calorimeter constants were determined in preliminary experiments with
reference substances: water, naphthalene, decane, and benzoic acid.
3. Results and discussion
HEAT CAPACITY AND ENTHALPY OF VAPORIZATION
We have not observed formation of glass or any other metastable state during
cooling cyclopentanol at a rate of (0.03 to 0.05) K·s−1 in experiments to study heat
capacity and phase transitions. Values of Cs of cyclopentanol obtained in this work
agree with Park et al.’s results(2) in the temperature ranges T=80 K to 120 K and 170 K
to 300 K (figure 1). Reasons for the substantial (up to 10 per cent) divergence of our
results from those of Parks et al. in the range T=(120 to 170) K are
not clear. However, the molar entropy for c-C5H9OH(l) Sm°(l, 298.15 K) =
(204.1420.90) J·K−1·mol−1 based on our measurements agrees satisfactorily with that
obtained by Parks et al.:(2) Sm°(l, 298.15 K)=206.3 J·K−1·mol−1. Values of the molar
heat capacity Cs, m(l, 298.15 K)=(182.4820.73) J·K−1·mol−1 from this work and
181.6 J·K−1·mol−1 from reference 14 also agree well.
Experimental values of the molar heat capacity of c-C5H9OH at saturation are given
in table 2. The characteristic Debye temperature evaluated from Cs values in the range
T=6 K to 15 K is 91.0 K. This value was used for extrapolation of Cs to T:0
according to Debye’s equation: CV, m=3R·D(UD/T).
Three solid-to-solid transitions were found for c-C5H9OH (figure 1): at T=176 K
with DtrsHm=(5725) J·mol−1; at T=202.6 K with DtrsHm=(3366214) J·mol−1 and at
T=234 K with DtrsHm=(5526) J·mol−1. The fusion temperature of c-C5H9OH is
255.6 K, and DfusHm=(122725) J·mol−1. Smoothed values of the molar heat capacity
of c-C5H9OH obtained by the least-squares method and other thermodynamic
properties are given in table 3.
The molar enthalpy of vaporization of c-C5H9OH (table 4) was determined in eight
experiments at the average temperature T=299.5 K. As a correction to 298.15 K is
too small and much less than the experimental uncertainty, this value was assigned to
T=298.15 K. Our value: DvapHm(298.15 K) = (57.0520.65) kJ·mol−1, is in an
agreement with that of Wadso:(15) vapHm(298.15 K)=(57.520.3) kJ·mol−1.
D
We obtained the experimental value of the gas-state standard molar entropy
of c-C5H9OH: Sm°(g, 340 K)=(362.922.4) J·K−1·mol−1 using the weight-averaged
value: DvapHm=(57.320.3) J·K−1·mol−1, calculated from our measurements and the

956
G. J. Kabo et al.
FIGURE 1. Temperature dependence of the molar heat capacity of c-C5H9OH. W, Parks et al.(2)
results of Wadso.(15) A necessary value of saturated vapor pressure was taken from the
equation:(16)
ln(p/kPa)=14.50171−3017.55/{(T/K)−108.25},
(1)
which describes the p=f(T) dependence in the temperature range T=346 K to 437 K.
For this purpose the liquid-phase molar entropy was extrapolated to T=340 K using
the equation for the molar heat capacity:
Cs, m/(J·K−1·mol−1)=−74.65+0.86242·(T/K),
(2)
and the enthalpy of vaporization was reduced to T=340 K taking into consideration
the molar heat-capacity difference DCp, m(l-to-g)=−80 J·K−1·mol−1 based on
experimental measurements for the liquid and statistical calculations for the gas.
CONFORMATIONAL COMPOSITION
The number of possible conformers for cyclopentanol is determined by the state of
the carbon ring (half-chair or envelope) and by the position and orientation of the OH–

TABLE 2. Experimental values of the molar heat capacity of c-C5H9OH at saturated vapor pressure
(R=8.31451 J·K−1·mol−1
)
a
a
a
ꢀTꢁ
K
Cp, m
R
DT
K
ꢀTꢁ
K
Cp, m
R
DT
K
ꢀTꢁ
K
Cp, m
R
DT
K
Series 1
7.532
7.568
7.716
7.928
8.158
8.403
8.639
8.866
9.120
9.419
9.737
10.11
10.47
10.58
11.23
11.48
11.74
11.79
11.72
11.89
11.95
11.91
12.27
12.93
14.18
14.03
14.31
14.51
15.61
15.12
15.26
15.33
15.52
15.78
16.09
16.57
18.82
16.77
17.18
17.16
17.73
19.39
26.01
38.91
50.98
64.04
23.98
18.40
18.48
18.65
19.04
19.40
19.83
20.21
20.66
21.08
21.51
298.41
302.92
21.97
22.45
Series 2
10.65
10.97
11.12
11.31
11.28
11.52
11.58
11.68
11.81
11.90
11.95
11.99
12.05
12.58
14.19
13.84
19.69
34.12
37.34
43.08
Series 3
12.38
12.49
12.79
13.02
13.65
14.21
16.83
13.63
13.21
12.97
13.11
13.15
13.78
14.03
14.26
14.56
14.85
15.25
15.70
29.72
34.64
38.75
47.48
59.94
79.17
4.28
4.23
208.20
15.26
1.28
99.27
100.98
103.60
107.86
112.42
116.82
121.09
125.25
129.29
133.74
138.59
143.31
147.91
152.40
156.78
159.61
160.72
161.63
162.55
163.46
164.38
165.29
167.40
171.54
176.45
181.23
185.85
190.61
195.25
205.72
207.92
211.22
215.58
219.91
224.19
228.43
232.53
235.16
237.13
238.02
241.03
245.03
249.45
252.01
252.97
253.80
254.84
256.33
257.91
261.09
265.88
270.61
275.30
280.04
284.72
289.32
293.88
1.13
2.28
2.97
4.64
4.48
4.34
4.21
4.10
4.00
4.91
4.77
4.65
4.53
4.43
4.33
1.33
0.92
0.92
0.92
0.91
0.91
0.91
3.28
4.92
4.72
4.70
4.77
4.72
4.56
2.18
2.17
4.36
4.31
4.27
4.22
4.15
3.94
1.20
0.82
0.82
3.19
4.66
4.08
0.99
0.84
0.72
1.27
1.42
1.42
4.67
4.62
4.57
4.52
4.47
4.42
4.37
4.33
Series 4
151.06
154.37
156.51
158.10
159.15
160.19
161.23
162.26
163.29
164.32
165.35
166.38
167.43
170.49
175.51
180.37
197.22
198.25
199.11
199.88
4.47
2.14
2.12
1.05
1.05
1.04
1.03
1.03
1.02
1.02
1.01
1.01
1.01
4.97
4.72
4.72
1.19
0.91
0.86
0.79
5.36
5.67
5.95
6.31
6.72
7.09
7.48
7.90
8.32
8.75
9.14
9.56
9.98
0.0433
0.0539
0.0616
0.0761
0.0918
0.110
0.128
0.153
0.177
0.204
0.236
0.265
0.356
0.353
0.423
0.498
0.570
0.635
0.709
0.810
0.925
1.045
1.171
1.312
1.437
1.556
1.682
1.848
2.046
2.230
2.424
2.679
2.945
3.152
3.409
3.669
3.920
4.232
4.543
4.842
5.166
5.433
5.665
5.935
6.148
6.395
6.627
6.819
7.020
7.258
7.506
7.749
7.985
8.205
8.412
0.33
0.30
0.27
0.44
0.39
0.36
0.44
0.39
0.46
0.41
0.37
0.46
0.38
0.84
0.73
0.76
0.68
0.62
0.70
1.02
0.90
1.09
0.98
1.03
0.94
0.86
1.18
1.39
1.66
1.49
1.70
1.90
1.95
2.12
2.35
2.64
2.82
4.03
3.56
4.33
3.88
3.66
4.56
4.20
3.93
4.51
4.23
4.02
5.18
4.91
4.68
4.50
4.33
4.19
4.00
10.63
11.41
12.16
12.88
13.53
14.18
15.04
16.00
16.99
18.03
19.03
20.01
20.92
21.94
23.22
24.74
26.31
27.90
29.70
31.62
33.66
35.90
38.39
41.13
44.55
48.35
52.29
56.39
60.15
64.53
68.64
72.69
76.91
81.27
85.39
89.98
95.02
99.80
104.39
108.80
113.05
117.21
169.53
170.80
171.93
172.93
173.91
174.87
175.78
176.74
177.75
178.75
179.75
180.73
185.54
187.26
190.20
191.54
193.21
195.18
196.81
197.94
198.85
199.66
200.36
200.93
201.36
1.27
1.26
1.00
0.99
0.97
0.96
0.90
0.97
0.98
0.98
0.98
0.97
1.71
1.69
1.34
1.33
1.97
1.95
1.28
0.96
0.88
0.83
0.73
0.62
0.51
0.43
0.37
0.30
0.31
0.42
1.03
1.29
1.28
1.28
201.67 100.08
201.93 119.48
202.13 151.86
202.27 148.85
202.49 102.41
203.11
204.28
205.59
206.90
25.84
15.01
15.15
15.12
a Average molar heat capacity for temperature interval DT with mean temperature ꢀTꢁ.

958
G. J. Kabo et al.
TABLE 3. Smoothed values of standard molar thermodynamic functions of c-C5H9OH in the condensed
state (R=8.31451 J·K−1·mol−1
)
T
T
T/K
Cp, m/R
D0 Hm°/RT
D0 Sm°/R
Fm°/R
Crystal IV
0
5
0
0
0
0
0.0391
0.2987
0.8047
1.435
2.082
2.718
3.291
3.807
4.272
4.691
5.412
6.013
6.537
7.027
7.507
8.008
8.573
9.204
9.899
0.0097
0.0772
0.2300
0.4514
0.7122
0.9944
1.282
1.566
1.841
2.106
2.599
3.045
3.449
3.819
4.165
4.491
4.807
5.120
5.437
5.759
6.091
6.434
6.646
0.0130
0.1032
0.3134
0.6300
1.019
1.456
1.919
2.392
2.868
3.340
4.261
5.142
5.980
6.778
7.544
8.282
9.003
9.713
10.42
11.13
11.84
12.57
13.00
0.0032
0.0260
0.0835
0.1787
0.3033
0.4615
0.6363
0.8262
1.027
1.234
1.663
2.097
2.531
2.959
3.379
3.791
4.196
4.593
4.984
5.370
5.752
6.132
6.358
10
15
20
25
30
35
40
45
50
60
70
80
90
100
110
120
130
140
150
160
170
176
10.66
11.48
12.37
12.94
Crystal III
176
180
190
200
12.94
13.33
14.35
15.43
15.73
6.685
6.828
7.197
7.581
7.684
13.04
13.34
14.09
14.85
15.05
6.358
6.510
6.889
7.268
7.367
202.6
Crystal II
202.6
210
220
230
234
14.90
15.33
15.93
16.56
16.82
9.682
9.873
10.13
10.40
10.51
17.05
17.59
18.32
19.04
19.33
7.367
7.717
8.183
8.639
8.819
Crystal I
234
240
250
255.6
16.82
17.21
17.90
18.30
10.54
10.70
10.97
11.13
19.35
19.79
20.50
20.90
8.819
9.088
9.530
9.775
Liquid
255.6
260
270
280
290
298.15
300
18.28
18.59
19.36
20.21
21.14
21.95
22.14
11.71
11.82
12.08
12.36
12.65
12.89
12.94
21.48
21.79
22.51
23.23
23.95
24.55
24.69
9.775
9.976
10.43
10.87
11.31
11.66
11.74

Properties of cyclopentanol
959
TABLE 4. Experimental determination of the molar enthalpy of vaporization of c-C5H9OH. The
vaporization enthalpy DvapH of specimens and the molar enthalpy DvapHm° were calculated from the
expression:
t=t
DH=K−1
·
2 DE·dt;
DvapHm°=DvapH·M/m;
g
t=0
where m is the specimen mass in vacuum; M is the molar mass; K is the calorimeter constant; DE is
the thermocouple potential difference corresponding to the temperature imbalance between cell and
calorimeter thermostat at the time t; t2 is the experiment duration; T is temperature of the calorimeter
t=t
2 DE·dt
T
K
m
g
Dh
DvapHm°
Type of
cell
N
J·g−1
kJ·mol−1
g
t=0
1
2
3
4
5
6
7
8
299.20
299.61
299.71
299.20
299.20
299.61
299.57
299.16
0.14998
0.15129
0.22133
0.19277
0.14479
0.17221
0.14559
0.23519
18291.32
18935.98
27548.04
24090.47
19222.51
22714.65
18963.72
30632.33
A
A
A
A
B
B
B
B
656.95
674.21
670.44
673.14
663.82
659.49
651.28
651.21
56.59
58.07
57.75
57.98
57.18
56.80
56.10
56.09
Note: K values for cells A and B are 185.65 mV·s·J−1 and 200.00 mV·s·J−1, respectively.
top. Calculations made by the molecular-mechanics method (MM2) led us to the
conclusion that the potential barrier of pseudorotation in c-C5H9OH (1.9 kJ·mol−1) is
substantially lower than that for rotation of the OH– top (about 7 kJ·mol−1). Such a
distinction allows us to consider internal rotation and pseudorotation in c-C5H9OH
as independent motions and to study pseudorotation at a fixed position of the OH–
top. The state of the carbon ring was not taken into consideration in the calculation
of the potential function of internal rotation of the OH– top.
Changes in potential energy during rotation of the OH– top (figure 2) may be
expressed by the following equation on the basis of our molecular-mechanics study:
Vm(8)/(kJ·mol−1)=3.36−2.10·cos(8)−0.20·cos(28)+2.30·cos(38),
(3)
where 8 is the angle of rotation.
It was found by the molecular-mechanics method, that only the half-chair (figure 3)
is a stable configuration of the carbon ring in cyclopentanol, and the following function
corresponds to energy changes during pseudorotation:
Vm( f )/(kJ·mol−1)=0.95+0.95·cos(2f ),
(4)
where f is the phase angle of pseudorotation (0EfQ2p).
Parameters of pseudorotation obtained in this work differ from those of reference 11.
The existence of two envelope conformers with axial and equatorial positions of the
OH– group was assumed in reference 11.

960
G. J. Kabo et al.
FIGURE 2. Potential-energy function of internal rotation of the OH– top in cyclopentanol and lowest
energy levels of internal rotation.
STANDARD MOLAR THERMODYNAMIC PROPERTIES OF c-C5H9OH IN THE
IDEAL-GAS STATE
To calculate the thermodynamic properties of cyclopentanol by statistical
thermodynamics we used the molar mass M=86.1335 g·mol−1. Principal moments of
inertia of molecule and reduced moment of inertia of the OH– top were obtained from
atomic coordinates calculated by the MM2 method. IA=134.19·10−47 kg·m2,
IB=271.51·10−47 kg·m2, IC=362.10·10−47 kg·m2; Ired(OH)=1.3·10−47 kg·m2. The
symmetry number of general rotation is 1. Studies of i.r. and Raman spectra of
cyclopentanol and its deuteroanalogues as well as calculation of normal vibrational
wavenumbers were made in reference 17. Vibration wavenumbers of c-C5H9OH taken
from reference 17 are listed:
(3653, 2970, 2970, 2906, 2906, 2871, 1473, 1437, 1382, 1268, 1250, 1213, 1183, 1142,
1083, 1001, 943, 893, 873, 789, 535, 467, 122, 2970, 2906, 2906, 2871, 1448, 1437,
1335, 1288, 1200, 1160, 1074, 1035, 906, 829, 753, 575, 412, 250, and 188) cm−1.

Properties of cyclopentanol
961
FIGURE 3. Conformers of cyclopentanol corresponding to energy minima and potential-energy function
for ring inversion.
In statistical calculations we did not take into consideration a wavenumber of
250 cm−1 corresponding to rotational vibration of the OH– top. Contributions of
its internal rotation to the thermodynamic properties were calculated by energy levels.
For this purpose 79 energy levels up to 393 kJ·mol−1 were generated by the variation
method on the basis of the potential energy function (equation 3) and reduced moment
of inertia 1.3·10−47 kg·m2 calculated by atomic coordinates. Wave functions of the free
rotator with moment of inertia 1.3·10−47 kg·m2 at quantum numbers from −39 to 39
were used as a basis for building of wave functions for the OH– top in a cyclopentanol
molecule.
An attempt to calculate contributions of pseudorotation to the thermodynamic
functions on the base of a corresponding vibrational wavenumber of 122 cm−1
taking into account the mixing of conformers led to the standard molar entropy of the

962
G. J. Kabo et al.
TABLE 5. Standard molar thermodynamic functions of c-C5H9OH in the ideal gas state (p°=101325 Pa,
R=8.31451 J·K−1·mol−1
)
T
T
T
K
D0 Sm°
Cp, m
R
D0 Hm°
Fm°
R
DfHm°
Df Gm°
R
RT
kJ·mol−1
kJ·mol−1
298.15
300
400
500
600
700
800
900
1000
41.86
41.94
46.21
50.45
54.56
58.48
62.21
65.74
69.08
12.68
12.76
17.08
20.93
24.14
26.79
29.02
30.91
32.52
7.897
7.927
9.679
11.56
13.40
15.12
16.73
18.20
19.55
33.97
34.02
36.53
38.89
41.16
43.36
45.48
47.54
49.53
−242.6
−242.8
−251.5
−258.4
−263.8
−267.7
−270.5
−272.4
−273.3
−112.4
−111.6
−66.5
−19.5
28.9
77.9
127.8
177.4
227.5
gas that is substantially lower than the experimental one. As was shown in
reference 17 this wavenumber determined for the crystalline state is not reliable, as
the lower vibrational wavenumbers of c-C5H9OH are shifted in the solid state
to the short-wave region, in comparison with gas-phase wavenumbers. Besides,
the mode of pseudorotation in cyclopentanol differs substantially from a vibrational
one due to a relatively low value of the potential barrier to pseudorotation (Vm, max
=
1.9 kJ·mol−1QRT at T=298.15 K), and a vibrational approximation could not
reproduce correctly its contributions to thermodynamic functions.
Hence, we did not use the wavenumber of 122 cm−1 in final statistical calculations
(table 5). Contributions of pseudorotation to the thermodynamic properties were
calculated on the basis of the classical approximation for the potential function
(equation 4) and reduced moment of inertia of 15.3·10−47 kg·m2. The value of the
pseudorotational moment of inertia was selected so that the calculated standard molar
entropy for the gas at T=340 K agrees with the experimental value.
Another experimental supporting value to prove results of statistical
calculations is the molar entropy of dehydrogenation of c-C5H9OH:
DrSm=(116.629.9) J·K−1·mol−1 at T=453.7 K.(18) The value of the standard molar
entropy of c-C5H9OH(g): Sm°(g, 453.7 K) = (392.4 2 10.0) J·K−1·mol−1 was obtained
using entropies of c-C4H8CO,(19) and H2,(20) at T=453.7 K: (366.3 and
142.7) J·K−1·mol−1, respectively. The standard molar entropy of c-C5H9OH from
statistical calculations is Sm°(g, 453.7 K)=403.1 J·K−1·mol−1. Divergence of this value
from the experimental one does not exceed the probable joint experimental
and calculational errors.
The molar heat capacity of c-C5H9OH(g) was measured in reference 21. The Cp, m
values found there differ substantially from those calculated in this work (table 6). Such
a great difference (about 17 J·K−1·mol−1) could not be explained by probable
uncertainties in molecular parameters of cyclopentanol. Moreover, correctness of the
experimental values of the molar heat capacity of c-C5H9OH(g),(21) seems to be doubtful
in view of the following comparison of experimental molar heat capacities of some
alcoholsandcorrespondingketones(table 7).ThedifferenceinCp, m betweenc-C5H9OH
and c-C4H8CO is expected to be much lower than follows from reference 21, and the
heat capacity of c-C5H9OH calculated in this work seems to be appropriate.

Properties of cyclopentanol
963
TABLE 6. Experimental(21) and calculated values of the molar heat capacity Cp, m of c-C5H9OH(g) at constant
pressure
T
K
C
p, m/(J·K−1·mol−1
)
expt.
calc.
420
430
440
450
460
470
480
168.120.8
169.221.2
172.321.6
175.421.6
178.422.0
181.522.5
184.622.9
148.6
152.0
155.3
158.5
161.7
164.8
167.9
The standard molar enthalpy and standard molar Gibbs free energy of formation
of c-C5H9OH(g) (table 5) were calculated on the basis of the value:
DfHm(g, 298.15 K)=−242.6 kJ·mol−1.(22)
PHASE TRANSITIONS OF CYCLOPENTANOL AND MOLECULAR ROTATION
IN CRYSTALS
We confirmed the existence of four different kinds of crystals of cyclopentanol(2) in our
experiments (see figure 1, table 1). A conclusion about the existence of c-C5H9OH in
the plastic-crystal state in the range T=202.6 K to 255.6 K may be made on the basis
of the relation of the molar transition entropy: DtrsSm(202.6 K)= 16.61 J·K−1·mol−1,
to the molar fusion entropy: DfusSm(255.6 K)= 4.80 J·K−1·mol−1. To estimate possible
contributions of different kinds of rotation to the molar transition entropy:
DtrsSm(202.6 K), we calculated the contributions of internal and general rotation of
isolated molecules of c-C5H9OH at T=202.6 K (ideal-gas state):
Sr°ot(OH– top)=13.2 J·K−1·mol−1;
Sr°ot(pseudorotation)=26.4 J·K−1·mol−1;
Sr°ot(IA)=36.0 J·K−1·mol−1;
Sr°ot(IB)=38.9 J·K−1·mol−1;
Sr°ot(IC)=40.1 J·K−1·mol−1.
TABLE 7. Experimental gas-phase molar heat capacities of some alcohols and corresponding ketones
C
p, m(g)
C
p, m(g)
DCp, m
Compound
Ref.
24
Compound
Ref.
25
J·K−1·mol−1
J·K−1·mol−1
J·K−1·mol−1
CH3COCH3
88.58
CH3CHOHCH3
108.1
19.5
17.6
29.7
10.9
(T=371.2 K, p=33.78 kPa)
(T=373.15 K, p=25.33 kPa)
CH3CHOHCH2CH3 142.7 27
(T=401.15 K, p=25.33 kPa)
CH3CH2COCH3
125.1
26
(T=397.15 K, p=25.16 kPa)
c-C4H8CO
139.5
(T=440 K, p:0)
175.6
28
28
c-C5H9OH
169.2
(T=440 K, p=?)
186.5
21
c-C5H10CO
c-C6H11OH
21
(T=440 K, p:0)
(T=440 K, p=?)

964
G. J. Kabo et al.
It is of high importance, that the molar entropy of phase transition of c-C5H9OH
into the plastic-crystal state: DtrsSm(202.6 K)=16.61 J·K−1·mol−1, is much less than the
contribution to the entropy arising only from the pseudorotation of isolated
molecules of c-C5H9OH at T=202.6 K. As was shown, molar entropies of similar
phase transitions for c-C5H10: DtrsSm(122.40 K) = 39.9 J·K−1·mol−1,(20) and for
c-C5H9Cl: DtrsSm(169.35 K)=52.8 J·K−1·mol−1,(1) are higher than corresponding
pseudorotational contributions. Absence of pseudorotation in the plastic-crystal state
seems to be unlikely due to the low value of its potential barrier. Hence, we consider
two variants to explain the relatively low value of DtrsSm(202.6 K) for c-C5H9OH.
1. Transformation of pseudorotation into vibrational ring inversion with a
relatively high potential barrier in the plastic crystal state.
2. Formation of molecular associates in the plastic crystal due to reorientation of
molecules in comparison with the rigid crystal and due to hydrogen bonding. In this
case, the entropy rise due to ‘‘melting’’ of pseudorotation in the plastic crystal
is compensated in part by the entropy reduction due to molecular association.
Undoubtedly, rotation of OH– tops is absent in molecules associated by H-bonds
involving OH– groups.
A conclusion about possible spherically symmetrical rotation of cyclopentanol
molecules in the plastic crystal based on measurements of dielectric properties(7) proved
to be questionable on the basis of the above entropy evaluations. One of the possible
explanations of changes in dielectric properties of cyclopentanol during
the (cr, III-to-cr, II) transition may be connected with the disappearance of any
prohibition to pseudorotation. Besides, values of the principal moments of inertia IA
and IC for c-C5H9OH molecules differ by a factor of about 3, causing a substantial
asymmetry of general molecular rotation.
A significant distinction in thermal behavior of cyclopentanol and of other
cyclopentane derivatives is shown by a comparison of entropies of related compounds
in the crystalline state at T=100 K and in the liquid state at T=298.15 K, and of
summedentropiesofphasetransitions(table8).Cyclopentanolhasananomalouslylow
value of liquid-state molar entropy and the lowest value of the difference
{Sm(l, 298.15 K)−Sm(cr, 100 K)}inanumberofcyclopentanederivatives(table8). The
summed value of the molar entropy of all phase transitions in the condensed state:
DSm, sum=22.0 J·K−1·mol−1 is also the lowest for c-C5H9OH, whereas the molar fusion
TABLE 8. Molar entropies of some c-C5H10 derivatives in the crystalline and liquid states and molar entropies of
transitions in the condensed state. SDtrsSm is the sum of molar entropies of all phase transitions between the
low-temperature rigid crystal and the liquid
Sm(cr, 100 K) Sm(l, 298.15 K)
DSm
Tfus
K
D
fusSm
SDtrsSm
Compound
Ref.
J·K−1·mol−1
J·K−1·mol−1
J·K−1·mol−1
J·K−1·mol−1
J·K−1·mol−1
c-C5H10
54.9
64.0
69.2
68.3
62.4
204.2
247.9
238.0
256.3
204.1
149.3
183.9
168.8
188.0
141.7
179.3
130.7
180.0
155.4
255.6
3.4
53.0
3.5
50.4
4.8
45.8
53.0
48.6
50.4
22.0
20
20
1
29
CH3-c-C5H9
c-C5H9Cl
c-C5H9SH
c-C5H9OH
this work

G. J. Kabo et al.
965
entropy: DfusSm=4.80 J·K−1·mol−1, is usual for plastic crystals. As DSm, sum for
c-C5H9OH is considerably less than the sum of contributions of pseudorotation and
internal rotation (OH– top) to the molar entropy calculated for isolated molecules
(ideal-gas state): Sm(pseudorot, 255.6 K)+ Sm(int.rot., 255.6 K)=42.55 J·K−1·mol−1
at Tfus=255.6 K, we may assume that these intramolecular degrees of freedom have
a rather high potential barrier in the liquid. Liquid cyclopentanol probably possesses
an anomalously high degree of order due to strong H-bonds. This fact is confirmed
also by the anomalous rise of the heat capacity of liquid cyclopentanol with rising
temperature (table 9): the value of {Cs, m(300 K)−Cs, m(260 K)} for c-C5H9OH
(29.5 J·K−1·mol−1) is higher than those for other liquid cyclopentane derivatives
(average: 10.5 J·K−1·mol−1) almost by a factor of 3. We may suppose, that such
anomalous rise of the heat capacity is tied with energy expensed for partial
decomposition of molecular associates. We estimated the energy of decomposition of
associates in the range T=260 K to 300 K using the heat-capacity difference of
cyclopentanol with its nearest analog cyclopentanone much less able to form
associates:
T=300 K
DEm=
DCs·dT=740 J·mol−1.
g
T=260 K
As the above value is much lower than usual energies of hydrogen bonding (about
20 kJ·mol−1), the equilibrium
nC5H9OH=(C5H9OH)n ,
in the liquid phase should be shifted to the right in the temperature range T=260 K to
300 K, and the degree of dissociation changes little even if the constant of dissociation
changes significantly at a temperature rise from T=260 K to T=300 K.
A high degree of association of cyclopentanol in the liquid state is also confirmed
indirectly by an anomalous high molar entropy of vaporization to the ideal-gas state:
S°(g, 298.15 K)−S(l, 298.15 K)=143.8 J·K−1·mol−1.
TABLE 9. Liquid-phase molar heat capacities and standard molar entropies of vaporization
(p°=101325 Pa) of some cyclopentane derivatives. DCs, m={Cs, m(300 K)−Cs, m(260 K)}
a
DCs, m
DvapSm°
Compound
Cs, m/(J·K−1·mol−1
)
Ref.
J·K−1·mol−1
J·K−1·mol−1
T=260 K
T=300 K
c-C5H10
c-C4H8S
CH3-c-C5H9
c-C5H9Cl
c-C5H9SH
c-C4H8CO
c-C5H9OH
115.5
131.7
145.5
143.9
156.3
145.1
154.6
127.5
140.7
159.6
152.8
165.7
155.0
184.1
12.0
9.0
14.1
8.9
9.4
9.9
88.7
102.1
91.0
101.5
104.6
106.0
143.8
20
20
20
1
29
26, 19
this work
29.5
a At T=298.15 K.

966
G. J. Kabo et al.
The molar entropy of vaporization of c-C5H9OH at the normal boiling temperature:
D
vapHm(414.0 K)=111 J·K−1·mol−1, (23) indicates a large deviation from Trouton’s rule.
Unfortunately, spectral study of c-C5H9OH in the wide temperature range T=96 K
to 252 K,(10) dedicated to study of conformational equilibrium, could not be interpreted
exactly, as information about accuracy in thermostating samples, about cooling rates,
and about possibilities to obtain non-equilibrium conformational composition of
cyclopentanol in spectroscopic apparatus is absent in reference 10. Complication of
i.r. spectra of c-C5H9OH at TQ203 K could be explained only taking into
consideration some details of experimental method not described in reference 10: the
way of cooling down to 96 K, cooling rate, character of temperature regime during
spectral registrations, etc.
Taking into account these circumstances, we made a thermodynamic analysis of
possibility for cyclopentanol to exist at TQ96 K as a mixture of conformers with
non-equivalent orientation of the OH– top. Such a possibility seems to be rather
grounded from consideration of temperature dependence of i.r. spectra.(10) If
this phenomenon takes place for cyclopentanol cooled under equilibrium conditions,
we have to assume existence of a residual molar entropy Sm°(T:0), which is equal
at least to 5.7 J·K−1·mol−1; that corresponds to mixing two non-equivalent conformers.
Such an assumption requires the addition of a corresponding correction
to the experimental molar entropy of c-C5H9OH, but in this case we could not find
any reasonable values of molecular parameters of cyclopentanol (vibration numbers,
barrier heights, and moments of inertia for internal rotation) to put the results of
statistical calculations of entropy into agreement with the corrected experimental
value.
That is why we assumed absence of residual entropy at T:0 for our samples of
cyclopentanol under conditions of calorimetric experiments {cooling rate of (0.03 to
0.05) K·s−1}. Thermodynamic results do not allow us to interpret the character of
structural changes during phase transitions of c-C5H9OH at T=176 K and 234 K with
small DtrsSm values.
REFERENCES
1. Diky, V. V.; Kabo, G. J.; Kozyro, A. A.; Krasulin, A. P.; Sevruk, V. M. J. Chem. Thermodynamics
1993, 25, 1169.
2. Parks, G. S.; Kennedy, W. D.; Gates, R. R.; Mosley, J. R.; Moore, G. E.; Renquist, M. L. J. Am. Chem.
Soc. 1956, 78, 56.
3. Kreutzenbeck, J.; Wurflinger, A. J. Phys. Chem. Solids 1978, 39, 193.
4. Wisotski, K. D.; Wurflinger, A. J. Phys. Chem. Solids 1981, 43, 13.
5. Adachi, K.; Suga, H.; Seki, S. Bull. Chem. Soc. Japan 1970, 43, 1916.
6. Labruyere-Verhavert, M. L. Bull. Soc. Chim. Belg. 1951, 60, 270.
7. Green, J. R.; Wheeler, D. R. Mol. Cryst. Liq. Cryst. 1969, 6, 1.
8. Corfield, G.; Davies, M. Trans. Faraday Soc. 1964, 60, 10.
9. Green, J. R.; Dalich, S. J.; Griffith, W. T. Mol. Cryst. Liq. Cryst. 1972, 17, 251.
10. Sciesinska, E.; Sciesinski, J.; Goldewska, M. Spectr. Lett. 1982, 15, 399.
11. Ekejiuba, I. O. C.; Hallam, H. E. J. Chem. Soc. B 1970, 209.
12. Lambert, J. B.; Xue, L.; Howton, S. C. J. Am. Chem. Soc. 1991, 113, 9858.
13. Sevruk, V. M.; Simirsky, V. V.; Kabo, G. Y.; Kozyro, A. A.; Krasulin, A. P. Zh. Fiz. Khim. 1990, 64,
3402.

Properties of cyclopentanol
967
14. Benson, G. C.; D’Arcy, P. J. J. Chem. Thermodynamics 1986, 18, 493.
15. Wadso, I. Acta Chem. Scand. 1966, 20, 544.
16. Ambrose, D.; Ghiassee, N. B. J. Chem. Thermodynamics 1987, 19, 903.
17. Durig, J. R.; Karriker, J. M.; Harris, W. C. Spectrochim. Acta 1971, 27A, 1955.
18. Fedoseenko, V. I.; Yursha, I. A.; Kabo, G. J. Doklady AN BSSR (Minsk) 1984, 28, 1109.
19. Diky, V. V.; Kabo, G. J. Doklady AN BSSR (Minsk) 1991, 35, 158.
20. TRC Thermodynamic Tables. Hydrocarbons. K. N. Marsh: Director. The Texas A&M University
System: College Station. 1994.
21. Vilcu, R.; Coman, B. Rev. Roum. Chim. 1975, 20, 603.
22. Thermochemical Data of Organic Compounds. II edition. Pedley, J. B.; Naylor, R. D.; Kirby, S. P.:
editors. Chapman and Hall: London. 1986.
23. Smith, B. D.; Srivastava, R. Thermodynamic Data for Pure Compounds. Part B. Elsevier: Amsterdam.
1986.
24. Pennington, R. E.; Kobe, K. A. J. Am. Chem. Soc. 1957, 79, 300.
25. Hales, J. L.; Cox, J. D.; Lees, E. B. Trans. Faraday Soc. 1963, 59, 1544.
26. Nickerson, J. K.; Kobe, K. A.; McKetta, J. J. J. Phys. Chem. 1961, 65, 1037.
27. Berman, N. S.; McKetta, J. J. J. Phys. Chem. 1962, 66, 1444.
28. Shvaro, O. V.; Peshchenko, A. D.; Sachek, A. I., et al. Inzh. Fiz. Zh. (Minsk) 1987, 52, 807.
29. Berg, W. T.; Scott, D. W.; Hubbard, W. N.; Todd, S. S.; Messerly, J. F.; Hossenlopp, I. A.; Ann Osborn,
Douslin, D. R.; McCullough, J. P. J. Phys. Chem. 1961, 65, 1425.