Enthalpies of Formation of Hexaethylethane, Octamethylhexane, and Tri-tert-butylmethane. Extremely Strained Hydrocarbons

Article abstract of DOI:10.1021/jo9702002

3,3,4,4-Tetraethylhexane (1) and 2,2,3,3,4,4,5,5-octamethylhexane (2) were synthesized from 3-ethylpentane and 2,2,3-trimethylbutane, respectively, by UV-irradiation with mercury in the gas phase. The enthalpies of combustion ΔH_c° of 1, 2, and tri-tert-butylmethane (3) when measured calorimetrically were ΔH_c° = -9467.2 ± 2.3, -9491.4 ± 2.3, and -8825.0 ± 4.3 kJ·mol^-1, respectively. The enthalpies of vaporization of 1 and 2 and the enthalpy of sublimation of 3 were derived from the temperature dependence of their vapor pressures. The latter were determined by a flow method. The resulting standard enthalpies of formation were ΔH_f° (g) = -265.5 ± 2.6, -248.3 ± 2.4, and -235.2 ± 4.3 kJ·mol^-1 for 1, 2, and 3, respectively. They correspond to strain enthalpies (H_s) of 118.1, 177.2, and 156.1 kJ·mol^-1, respectively, These values provide valuable test cases for semiempirical and empirical calculations.

Full text of DOI:10.1021/jo9702002

J . Org. Chem. 1997, 62, 4683-4686
4683
En th a lp ies of F or m a tion of Hexa eth yleth a n e, Octa m eth ylh exa n e,
†
a n d Tr i-ter t-bu tylm eth a n e. Extr em ely Str a in ed Hyd r oca r bon s
Sergey P. Verevkin, Margot N o¨ lke, Hans-Dieter Beckhaus, and Christoph R u¨ chardt*
Institut f u¨ r Organische Chemie und Biochemie der Universit a¨ t Freiburg,
Albertstr.21, D-79104 Freiburg i. Br., Germany
Received February 4, 1997X
3
3
,3,4,4-Tetraethylhexane (1) and 2,2,3,3,4,4,5,5-octamethylhexane (2) were synthesized from
-ethylpentane and 2,2,3-trimethylbutane, respectively, by UV-irradiation with mercury in the gas
phase. The enthalpies of combustion ∆H
c
° of 1, 2, and tri-tert-butylmethane (3) when measured
-
1
calorimetrically were ∆H
c
° ) -9467.2 ( 2.3, -9491.4 ( 2.3, and -8825.0 ( 4.3 kJ ‚mol ,
respectively. The enthalpies of vaporization of 1 and 2 and the enthalpy of sublimation of 3 were
derived from the temperature dependence of their vapor pressures. The latter were determined
by a flow method. The resulting standard enthalpies of formation were ∆H
f
° (g) ) -265.5 ( 2.6,
-
1
-
248.3 ( 2.4, and -235.2 ( 4.3 kJ ‚mol for 1, 2, and 3, respectively. They correspond to strain
1
-
enthalpies (H
s
) of 118.1, 177.2, and 156.1 kJ ‚mol , respectively. These values provide valuable
test cases for semiempirical and empirical calculations.
In tr od u ction
Syn th esis
The best synthetic procedure4,7 for 1 and 2, so far, has
2
Sterically congested hydrocarbons exhibit the impor-
•
been the dimerization of tertiary radicals R , generated
by photolysis of the corresponding azo compounds
tant principle that steric effects increase the energy of a
molecule, as measured as its heat of formation.3 In-
tramolecular van der Waals repulsions are responsible
for this excess energy, the so-called strain energy, which
RsNdNsR).8 The competing disproportionation pre-
(
dominates, however, and causes low yields of the dimers
9
R-R. We applied, therefore, a new method that was
2
causes unique structural distorsions. Elongated bonds
introduced recently for the synthesis of highly strained
dimers by mercury-sensitized photolysis of “monomers”
RH and successfully synthesized 3,3,4,4-tetraethylhexane
(1) and 2,2,3,3,4,4,5,5-octamethylhexane (2) in 22% and
16% yields, respectively. By distillation in a spinning
band column a purity >99.9% was reached. A great
advantage of this simple method is that the starting
materials are readily accessible and cheap.
up to 165 pm4b are found especially between two quater-
4
nary carbon atoms and enlarged bond angles (to more
than 120°) at tertiary carbons. The strain of branched
hydrocarbons is demonstrated by their unique thermo-
lability and by the ease of their homolytic cleavage
reactions into alkyl radicals. Whereas 2,2,3,3-tetra-
5
6
methylbutane, often called hexamethylethane, is stable
up to 400 °C, 3,3,4,4-tetraethylhexane, i.e., hexaethyl-
ethane (1),4 has a half-life of only 1 h at 280 °C.
a,7
Although the heats of formation ∆H
,2,3,3,4,4,5,5-octamethylhexane (2) and, hence, their
experimentally determined strain energies H are of
f
° (g) of 1 and
2
s
general interest and should be useful as test cases for
the development of calculational procedures, no measure-
ments have been possible so far because of synthetic
Resu lts
problems, which are common to all structures with two
4
neighboring quaternary carbons (“C
q
-C
q
ethanes” ).
The standard enthalpies of combustion ∆H
c
° were
In this context, we also
measured calorimetrically.1
0,11
†
Thermolabile Hydrocarbons. 32. Part 31: see ref 1.
*
To whom correspondence should be addressed. Fax: 49 (0)761-
(8) Duismann, W.; Beckhaus, H.-D.; R u¨ chardt, C. Liebigs Ann.
Chem. 1974, 1348.
2
03-5987. E-mail: ruechardt@oca.chemie.uni-freiburg.de.
X
Abstract published in Advance ACS Abstracts, J une 15, 1997.
(9) (a) Brown, S. H.; Crabtree, R. H. J . Chem. Soc. Chem. Commun.
1987, 970. (b) Brown, S. H.; Crabtree, R. H. Tetrahedron Lett. 1987,
28, 5599. (c) Brown, S. H.; Crabtree, R. H. J . Chem. Educ. 1988, 65,
290. (d) Brown, S. H.; Crabtree, R. H. J . Am. Chem. Soc. 1989, 111,
2935. (e) Muedas, C. M.; Ferguson, R. R.; Crabtree, R. H. Terahdron
Lett. 1989, 30, 3389. (f) Boojamra, C. G.; Crabtree, R. H.; Ferguson,
R. R.; Muedas, C. Tetrahedron Lett. 1989, 30, 5583. (g) Ferguson, R.
R.; Boojamra, C. G.; Brown, S. H.; Crabtree, R. H. Heterocycles 1989,
28, 121. (h) Ferguson, R. R.; Crabtree, R. H. New J . Chem. 1989, 13,
647. (i) Muedas, C. M.; Ferguson, R. R.; Brown, S. H.; Crabtree, R. H.
J . Am. Chem. Soc. 1991, 113, 2233. (j) Ferguson, R. R.; Crabtree, R.
H. J . Org. Chem. 1991, 56, 5503. (k) Krajnik, P.; Michos, D.; Crabtree,
R. H. New J . Chem. 1993, 17, 805. (l) Genkinger, O.; Bargon, J .
Tetrahedron Lett. 1996, 37, 6853-6856.
(
1) Herberg, K.; Verevkin, S. P.; N o¨ lke, M.; Beckhaus, H.-D.;
R u¨ chardt, C.; Liebigs Ann. 1995, 515-522.
2) R u¨ chardt, C.; Beckhaus, H.-D. Angew. Chem. 1985, 97, 531-
40; Angew. Chem., Int. Ed. Engl. 1985, 24, 529-538.
3) Greenberg, A.; Liebman, J . F. Strained Organic Molecules;
Organic Chemistry Series 38; Academic Press: New York, 1978.
4) (a) Winiker, R.; Beckhaus, H.-D.; R u¨ chardt, C. Chem. Ber. 1980,
13, 3456-3476. (b)Flamm-ter Meer, M. A.; Beckhaus, H.-D.; Peters,
K.; v. Schering, H.-G.; R u¨ chardt, C. Chem. Ber. 1985, 118, 4665.
5) (a) Flamm-ter Meer, M. A.; Beckhaus, H.-D.; R u¨ chardt, C.
(
5
(
(
1
(
Thermochim. Acta 1984, 80, 81-89. (b) Beckhaus, H.-D.; Kratt, G.;
Lay, K.; Geiselmann, J .; R u¨ chardt, C.; Kitschke, B.; Lindner, H. J .
Chem. Ber. 1980, 113, 3441-3455. (c) Flamm-ter Meer, M. A.;
Beckhaus, H.-D.; Peters, K.; v. Schering, H.-G.; Fritz, H.; R u¨ chardt,
C. Chem. Ber. 1986, 119, 1492-1510.
(10) Beckhaus, H.-D.; R u¨ chardt, C.; Smisek, M. Thermochim. Acta
1984, 79, 149-159.
(11) Hubbard, W. N.; Scott, D. W.; Waddington, G. In Experimental
Thermochemistry; Rossini, F. D., Ed.; Interscience Publishers: New
York, 1956; pp 75-127.
(
6) (a) Good, W. D. J . Chem. Thermodyn. 1972, 4, 709. (b) Bauer, S.
H.; Beach, J . Y. J . Am. Chem. Soc. 1942, 64, 1142.
7) Beckhaus, H.-D.; R u¨ chardt, C. Tetrahedron Lett. 1973, 15,1971.
(
S0022-3263(97)00200-4 CCC: $14.00 © 1997 American Chemical Society

4
684 J . Org. Chem., Vol. 62, No. 14, 1997
Verevkin et al.
Ta ble 1. Exp er im en ta l Th er m och em ica l Resu lts a n d MM2 Ca lcu la tion s for Com p ou n d s 1-3 a t 298 K (k J m ol-1)
state
∆Hc°(l or cr)a
∆Hf°(l or cr)
∆Hvap° b
∆Hf°(g) (exptl)
∆Hf°(g) (MM2)
Hs (exp.)
1
2
3
l
l
cr
-9467.2 ( 2.3
-9491.4 ( 2.3
-8825.0 ( 4.3
-329.4 ( 2.3
-305.2 ( 2.3
-292.2 ( 4.3
63.9 ( 1.2c
-265.5 ( 2.6
-248.3 ( 2.4
-235.2 ( 4.3
-260.5
-253.5
-236.0
118.1
177.2
156.1
56.90 ( 0.70e
d
57.03 ( 0.43
a
Taken from the specific enthalpies of combustion in Table 4. b From Table 5, the mean temperatures of the measurements are about
c
d
2
90-310 K. Slightly different from the preliminary result given in ref 16. The value for the enthalpy of combustion of 3 from our
12 12
previous work proved to be incorrect, due to sensitivity to oxygen; the enthalpy of sublimation was also in error due to the condensation
e
of water. These interferences were eliminated by precautions mentioned in the Experimental Section. Enthalpy of sublimation. The
value of ∆Hsub,T° has been independently determined for 3 to be 58.6 kJ ‚mol by the head-space technique.
-
1
16
-
1
Ta ble 2. P u r ities, Den sities d (293K), Sp ecific Hea ts cp(298K),
strained are tri-tert-butylmethane 3 (H
and hexaethylethane (1) (H
) 155.2 kJ‚mol )
s
a n d Exp a n sion Coefficien ts of th e Ma ter ia ls
-1
s
) 123.1 kJ ‚mol ). In spite
of this high strain, the enthalpies of formation ∆H ° (g)
f
a
b
-6 c
purity
%)
d(293K)
cp(298K)
-1
(δV/δT) 10
(
(g cm-1)
(J K g-1
)
(L g
-1
K
-1)
-1
of 1-3 were well reproduced (within 4-5 kJ ‚mol , see
Table 1) by MM2 force-field calculations.17 The specific
structural features of the symmetrically hexaalkylated
1
2
3
99.99
99.94
99.99
0.859
0.857
0.850
1.50
2.31
2.13
1.92
1.67
1.32
1.0
1.0
0.1
0.1
0.1
18
ethanes 1 and 2 have been described in an earlier paper.
d
cotton
mylar
e
It has been shown that a strong interplay between the
six geminal and vicinal alkyl groups, which may be called
dynamic gearing, determines the symmetry of the struc-
tures, and often the anti conformation becomes less stable
1.38
a
b
Measured by the suspension method. From DSC measure-
c
d
ments. Estimated. CH1.774O0.887, ∆uc°(cotton) ) -16 945.2 ( 4.2
J g
-
1
e
-1
. C10H8O4, mylar A ∆uc°(mylar) ) -22 831.0 ( 4.8 J g
(
g
combustion of 1 and 3), mylar B ∆uc°(mylar) ) -22 744.8 ( 1.5 J
than the gauche one. 1 adopts C
ethyl groups at each C atom in the anti-conformation
and the other in the gauche-conformation. The confor-
mation at the central C -C bond of 1 is defined by the
2
symmetry with two
-
1
-5
(combustion of 2), m(mylar) ) mmoist[1 - 4.64 × 10 (relative
q
moisture of air in %)].
q
q
reinvestigated12 tri-tert-butylmethane 3 because we dis-
covered that this compound reacts with oxygen in the
calorimetric bomb at 30 atm prior to ignition. To avoid
this autoxidation, the samples for combustion were
prepared in a glovebox under N and were sealed in
2
mylar bags. For 3, measurements in two different
calorimeters gave identical results.
two gauche ethyl groups in the gauche position to each
other. 2 adopts a preferred conformation with tert-butyl
groups in the anti position (for a detailed description see
ref 18). These strong steric interactions of alkyl groups,
mainly intramolecular van der Waals repulsions, serve
as a valuable test case for other calculational procedures.
The enthalpies of vaporization ∆Hvap° of 1 and 2 and
Exp er im en ta l Section
∆
H
sub° for 3 were obtained from the temperature depen-
dence of the vapor pressures measured in a flow sys-
Gen er a l Meth od s. The analytical instruments used had
tem.1
perimental basis for the quantitative estimation of the
strain enthalpies H of 1-3. They are derived as a
difference between the experimental ∆H ° (g) and the sum
of strain-free increments for alkanes.15
3,14
These thermochemical data constitute the ex-
been described in a previous publication.1
Ma ter ia ls. Syn th esis a n d P u r ifica tion . The best syn-
thesis for the highly strained molecules 1 and 2 is to dimerize
s
16
19
f
3
-ethylpentane and 2,2,3-trimethylbutane, respectively, by
9
the mercury-photosensitized dehydrodimerization. The ex-
periments were carried out in a cylindrical 1 L quartz vessel
with an attached condenser. At the bottom of the vessel was
attached a small Pyrex flask by a ground joint containing about
A summary of the results from these measurements
is given in Table 1. The given standard deviations of the
mean include the uncertainties from calibration and the
uncertainties from the combustion energies of the aux-
iliary materials.
3
0-50 mL of the liquid monomer and, in addition, a drop of
mercury. The substrate was refluxed, and simultaneously the
vapor phase was irradiated (254 nm). The reaction was
controlled by following the generation of hydrogen in a gas
burette, which was attached to the condenser. The temper-
ature of the condenser was kept at -30 °C to avoid the transfer
of material in the gas stream.
Discu ssion
s
The strain enthalpies H , which are due to steric
repulsion between the bulky alkyl groups, are derived
from the difference between the experimental standard
3-Ethylpentane and 2,2,3-trimethylbutane were synthesized
following the literature procedure.19
3-Eth ylp en ta n e:19 1H-NMR (250 MHz, CDCl
, TMS) δ 0.81
3
enthalpies of formation ∆H
the sum of the appropriate strain-free increments (CH
f
° (g) of the molecules 1-3 and
1
5
(t, 9H, CH ), 1.08 (sept, 1H, (CH CH ) 3CH), 1.26 (q, 6H,
-
3
3
2
3
(
CH
3
CH
2
CH); bp 92 °C.
[
C] ) -42.05, CH [2C] ) -21.46, CH[3C] ) -9.04 and
2
2,2,3-Tr im eth ylbu tan e:19 1H-NMR (250 MHz, CDCl , TMS)
-1
C[4C] ) -1.26 kJ ‚mol ). They are listed in Table 1. The
most strained compound in this series is octamethylhex-
ane (2) with the strain H
3
δ 0.83 (d, 6H, (CH
C(CH CH); bp 80 °C.
,3,4,4-Tetr a eth ylh exa n e (1). Twenty-five g of 3-ethyl-
3 2 3 3
) CH), 0.84 (s, 9H, C(CH ) ), 1.35 (sept, 1H,
) 172.0 kJ ‚mol-
1
.
Less
3 2
)
s
3
pentane was irradiated under reflux for 8 d (generation of 2.4
(
12) Flamm-ter Meer, M. A.; Beckhaus, H.-D.; R u¨ chardt, C. Ther-
mochim. Acta 1986, 107, 331-338.
13) Cox, J . D.; Pilcher, G. In Thermochemistry of Organic Com-
pounds; Academic Press: London, 1970.
14) Bernl o¨ hr, W.; Beckhaus, H.-D.; R u¨ chardt, C.; Peters, K.; von
Schnering, H. G. Chem. Ber. 1984, 117, 1013-1018.
15) Schleyer, P. v. R.; Williams, J . E.; Blanchard, K. B. J . Am.
Chem. Soc. 1970, 92, 2377.
16) Chickos, J . S.; Hesse, D. G.; Hosseini, S.; Liebman, J . F.;
L of hydrogen) and purified by distillation of the residue: 5.5
1
g (22%) of 1; H-NMR (250 MHz, CDCl
3
, TMS) δ 0.90 (t, 18H,
(
1
3
2 3 2 3
6 CH CH ), 1.49 (q, 12H, 6 CH CH ); C-NMR (20 MHz,
(
(
(17) Allinger, N. L. J . Am. Chem. Soc. 1977, 99, 8127-8134.
(18) Beckhaus, H.-D.; R u¨ chardt, C.; Anderson, J . E. Tetrahedron
1982, 38, 2299-2309.
(19) Edgar, G.; Calingaert, G.; Marker, R. E. J . Am. Chem. Soc.
1929, 51, 1487.
(
Mendenhall, G. D.; Verevkin, S. P.; Rakus, K.; Beckhaus, H.-D.;
R u¨ chardt, C. J . Chem. Thermodyn. 1995, 27, 693-705.

Enthalpies of Formation of Strained Hydrocarbons
J . Org. Chem., Vol. 62, No. 14, 1997 4685
Ta ble 3. Resu lts fr om Typ ica l Com bu stion Exp er im en tsa
1
2
3 (in macro)
3 (in micro)
b
m(substance) (g)
0.255 518
0.000 685
0.022 664
0.506 26
-12 701.41
-6.61
0.163 372
0.000 677
0.021 372
0.330 88
-8301.31
-4.23
0.224 001
0.000 700
0.033 007
0.457 22
-11 471.11
-5.86
0.033 593
0.000 800
0.008 769
1.295 42
-1818.58
-3.51
b
m′(cotton) (g)
b
m′′(mylar) (g)
c
∆
Tc (K)
c
ꢀ
calor(-∆Tc) (J )
cont(-∆Tc) (J )
ꢀ
d
∆
Ecorr. (J )
3.22
1.46
3.18
2.13
d
-
m′∆u′c (J )
11.67
517.44
-47 645.3
-9470.48
-326.10
11.46
488.1
-47 758.27
-9492.87
-303.67
11.88
755.42
-47 794.67
-8828.49
-288.78
13.56
200.29
-47 812.66
-8831.80
-285.43
d
-
m′′∆u′′c (J )
∆
∆
∆
uc(substance) (J g-1)
H°c(substance) (kJ mol 1)
-
-
1
H°f(substance) (kJ mol
)
a
i
i
For the definition of the symbols see ref 11. Macrocalorimeter:Th ) 298 K; Vbomb ) 0.2664 L; p gas ) 30.45 bar; m water ) 0.78 g;
i
i
Eignition ) 1.5 J ; mplatin ) 9.77 g. Microcalorimeter:Th ) 298 K; Vbomb ) 0.0460 L; p gas ) 30.45 bar; m water ) 0.23 g; Eignition ) 1.5 J ; mplatin
b
c
f
i
-1
)
2.37 g. Corrected masses obtained from weight by calculating the buoyancy. ∆Tc ) T - T + ∆Tcorr, ꢀcalor ) 25 088.9 ( 2.6 J K
1 i
-
(
0.010%) for 1-3 (in macro), ꢀcalor ) 1403.86 ( 0.22 J K (0.015%) for 3 (in micro), from calibration with benzoic acid; ꢀcont(-∆Tc) ) ꢀ cont
i f f d
(
T - 298 K) + ꢀ cont (298 K - T + ∆Τcorr). ∆Ecorr is sum of items 81-85, 87-90, 93, and 94 in ref 11.
Ta ble 4. Sp ecific En er gies of Com bu stion -∆u c° (J g-1)
a s th e Resu lt of All Com bu stion Exp er im en ts for
Com p ou n d s 1-3
Ta ble 5. Va p or P r essu r es p Deter m in ed by th e
Tr a n sp ir a tion Meth od
∆
Hvap,T° or
∆Hsub,T°
3a
3b
e
1
2
Ta (K)
mb (mg)
VN2 (L)
c
pd (mbar)
(kJ mol )
-1
4
4
4
4
4
7 645.3
7 598.0
7 618.9
7 656.6
7 624.8
47 747.4
47 779.2
47 790.5
47 731.1
47 758.3
47 794.7
47 791.3
47 629.8
47 716.0
47 737.3
47 812.7
47 874.2
47 847.4
47 752.5
47 802.2
-
-
-
-
-
-
-
2
1
1
1
1
2
2
-3
-3
-2
-2
-2
-2
-2
1
2
282.9 9.07 × 10
287.2 1.17 × 10
293.0 1.48 × 10
297.3 1.15 × 10
302.3 1.72 × 10
303.0 9.20 × 10
307.3 8.90 × 10
288.9 2.92
299.3 1.29
299.3 2.12
04.3 1.73
04.3 1.29
2.126 5.434 × 10
1.733 8.540 × 10
1.264 1.473 × 10
0.696 2.075 × 10
0.642 3.358 × 10
0.340 3.391 × 10
0.240 4.644 × 10
17.890 2.303 × 10
3.200 5.298 × 10
5.280 5.310 × 10
2.810 7.898 × 10
2.280 7.361 × 10
1.190 1.545 × 10
0.945 2.308 × 10
0.610 3.072 × 10
14.060 1.050 × 10
3.171 2.297 × 10
8.210 4.110 × 10
1.760 4.085 × 10
4.760 6.079 × 10
0.599 7.236 × 10
3.070 9.195 × 10
2.140 1.400 × 10
2.090 2.069 × 10
1.130 2.964 × 10
1.180 4.120 × 10
0.837 6.209 × 10
63.9 ( 1.2
4
4
7 719.4
7 729.8
mean value:
7 628.7
4
47 750.8
47 775.8
-
2
56.90 ( 0.70
a
Experiments in the macrocalorimeter. b Experiments in the
-2
-
-
-
-
-
-
2
2
2
1
1
1
microcalorimeter.
3
3
CDCl
10, M /2), 57 (100, C
3
) δ 11.0 (CH
3
), 27.5 (CH
2
), 44.0 (C); MS (70 eV) m/ z 99
+
+
314.4 1.44
19.4 1.72
24.5 1.49
(
4
H
9
). Anal. Calcd for C14 30 (198.39):
H
3
3
C, 84.76; H, 15.24. Found: C, 84.57; H, 15.05. The product
was purified by distillation in a spinning band column, bp 80
-
2
°
C (0.6 Torr). After purification, no impurities >0.001% could
be detected in the sample by GC.
,2,3,3,4,4,5,5-Octa m eth ylh exa n e (2). A 3.97 g (16%)
3
264.7 1.09
57.03 ( 0.43
(sublimation)
-
-
-
1
1
1
-2
272.9 5.39 × 10
-
2
2
2
2
2
2
2
2
3
3
3
78.5 2.44
79.1 5.34 × 10
83.6 2.11
84.6 3.22 × 10
88.6 2.08
93.5 2.21
98.4 3.20
03.3 2.48
08.4 3.61
13.7 3.86
2
-2
sample of 2 was obtained by irradiation of 25 g of 2,2,3-
trimethylbutane under reflux for 18 d (generation of 1.8 L of
hydrogen) and distillation of the residue: 1H-NMR (250 MHz,
-
2
-2
-
-
2
1
CDCl
3
, TMS) δ 1.00 (s, 18 H, C(CH
3
)
3
), 1.18 (s, 12H, C(CH
) δ 22.73 (CH C, 30.01 (CH
C; MS (70 eV) m/ z 141 (9, M
3 2
) C);
1
3
C NMR (20 MHz, CDCl
1.43 ((CH C, 46.47 (CH
3
3
)
2
3
)
3
+
C,
-
-1
-1
-1
-1
4
3
)
2
3
)
3
+
+
+
9
C
4
H
9
), 99 (19, M /2), 57 (100, C
4
H
). Anal. Calcd for C14
H
30
(
198.39): C, 84.76; H, 15.24. Found: C, 84.45; H, 15.42. The
product was purified in a spinning band column, bp 65 °C (0.6
318.6 4.00
0.619 8.687 × 10-1
9
d
Torr) [lit. bp 102 °C (12 Torr)], purity >99.94%.
a
Temperature of saturation, N2 gas stream 0.95-1.88 L h-1.
Mass of transferred sample by cooling to the temperature of
Tr i-ter t-Bu tylm eth a n e (3) was prepared and purified by
recrystallization and sublimation by the previous procedure,12
mp 83 °C. After purification, no impurities (>0.001%) could
be detected in the sample of 1 by GC.
Com bu stion Ca lor im etr y. Compounds 1 and 2 were
stable under bomb conditions. Tri-tert-butylmethane (3) is
sensitive to oxygen; therefore, the preparation of the samples
for combustion experiments was performed in a glovebox under
b
c
condensation Tcond ) 243 K. Amount of nitrogen used to transfer
the mass m of the sample. d Vapour pressures at temperatures T
of experiment, corrections for residual vapor pressure at Tcond were
made. e T corresponds to to the average of the temperature applied
for the measurements (see column 2).
Results for typical combustion experiments of each com-
pound are given in Table 3. The individual values of the
specific enthalpies of combustion and the mean values are
listed in Table 4.
2
N . The combustion experiments for the liquids 1 and 2 and
the solid sample of 3 were performed in sealed mylar bags in
1
a macrocalorimeter with a stirred water bath. Measurements
of the heat of combustion of 3 were, in addition, performed in
En th a lp ies of Va p or iza tion or Su blim a tion . Tr a n sp i-
r a tion Meth od . The enthalpies of vaporization ∆Hvap° of 1
and 2 and of sublimation ∆Hsub° for 3 were determined by
1
0
an isoperibolic microcalorimeter, and no differences between
both series of measurements were found. The energy equiva-
lents of the calorimeters were calibrated with a standard
reference sample of benzoic acid (sample SRM 39i, National
means of the method of transference in a saturated N
2
stream.1
3,14
The substances were mixed with glass beads and
1
1
Bureau of Standards). Conventional procedures were used
for the reduction of the data to standard conditions. The
densities of the substances were determined with the suspen-
sion method. The specific heat capacities were measured by
DSC (Table 2).
filled into a thermostated U-shaped tube. At several temper-
atures, a slow stream of nitrogen was passed through the
U-shaped tube, and the transported amount of material was
condensed in a trap cooled to -30 °C. Its mass was determined
by GC analysis after addition of an internal standard, and the

4
686 J . Org. Chem., Vol. 62, No. 14, 1997
Verevkin et al.
vapor pressure p was calculated from these data and the
residual vapor pressure at the condensation temperature.13
The latter and the enthalpies of sublimation or vaporization,
Ack n ow led gm en t. Thanks are due to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for financial support and to F. Schillinger and
E. Hickl for technical assistance.
respectively, were calculated by the following equation: ∆Hvap
°
)
-R[d ln (p)/dT] (with R ) gas constant, T ) temperature).
The enthalpies of vaporization and sublimation at 298 K are
recorded in Table 5.
J O9702002