Intermolecular Interactions
FULL PAPER
prepared according to litterature procedures. The synthesis of 22’, 23’, 43,
5
0’,0, 53’,0, 53’,2, 50’,3, 52’,3, 53’,3, 6, 7, C12L0’,0, C12L3’,0, C12L2’,0, C12L0’,3
,
C12L2’,2, C12L3’,2, C12L2’,3, C12L3’,3 and C12L0’,2 are given in Appendix 6
(Supporting information). Acetonitrile and dichloromethane were distil-
led over calcium hydride. Silicagel plates Merck 60 F254 were used for
thin layer chromatography (TLC) and Fluka silica gel 60 (0.04–
0.063 mm) or Acros neutral activated alumina (0.050–0.200 mm) was
used for preparative column chromatography.
Spectroscopic and analytical measurements: 1H and 13C NMR spectra
were recorded at 258C on a Bruker Avance 400 MHz spectrometer.
Chemical shifts are given in ppm with respect to TMS. Pneumatically-as-
sisted electrospray (ESI-MS) mass spectra were recorded from 10ꢀ4 m sol-
utions on an Applied Biosystems API 150EX LC/MS System equipped
with a Turbo Ionspray source. Elemental analyses were performed by
K. L. Buchwalder from the Microchemical Laboratory of the University
of Geneva. TGA were performed with a thermogravimetric balance Met-
tler Toledo Star Systems (under N2). DSC traces were obtained with a
Mettler Toledo DSC1 Star Systems differential scanning calorimeters
from 3–5 mg samples (5 and 0.58Cminꢀ1, under N2). The characterization
of the mesophases and of the isotropic liquids were performed with a po-
larizing microscope Leitz Orthoplan-Pol with a Leitz LL 20x/0.40 polariz-
ing lens, and equipped with a Linkam THMS 600 variable-temperature
stage. The variable-temperature FT-IR spectra were recorded on an
IRTF Nicolet iS10 spectrometrer in diffuse reflectance mode by using a
high-temperature diffuse reflectance environmental chamber. The sam-
ples were diluted into a KBr matrix and the resulting mixtures containing
about 10% of compound were ground before being heated at 2008C
during few minutes. After cooling to room temperature the FT-IR spec-
tra were recorded in the 20–2008C and in the 200–208C temperature
ranges using a heating or cooling rate of 28Cminꢀ1. The spectra were re-
corded with a resolution of 0.4 cmꢀ1. The mathematical analyses were
performed by using Igor Pro (WaveMetrics Inc.) and Excel (Microsoft)
softwares.
Figure 9. Plots of a) the cohesion free energy densities (CFED) versus
the melting temperature (Tm) and b) the molar volumes (Vm) versus DSm
for saturated linear hydrocarbons CnH2n+2. The dotted trace shows the
theoretical curve computed with Equation (17).
X-ray crystallography: A summary of crystal data, intensity measure-
ments and structure refinements for C12L3’,0, C12L2’,0, C12L0’,2, C12L3’,2
,
C12L2’,3 and C12L3’,3 is given in Table S1 (Supporting Information). All
crystals were mounted on quartz fibers with protection oil. Cell dimen-
sions and intensities were measured at 180–200 K on a Agilent Supernova
diffractometer with mirror-monochromated CuKa radiation (l=
1.54187 ꢃ) and CCD camera. Data were corrected for Lorentz and polar-
ization effects and for absorption. The structures were solved by direct
methods (SIR97),[46] all other calculation were performed with
SHELXL[47] systems and ORTEP[48] programs. CCDC-917848 (C12L3’,0),
CCDC-917849 (C12L2’,0), CCDC-917850 (C12L0’,2), CCDC-917851
(C12L3’,2), CCDC-917852 (C12L2’,3), and CCDC-917853 (C12L3’,3) the sup-
plementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
sane (C24H50)[41] is translated into a molar volume of Vm =
444.5 cm3 molꢀ1, from which a molar entropy of DSm =
254 Jmolꢀ1 K can be estimated with Equation (17). Equa-
tion (14) then provides the melting temperature Tm =312 K,
whereas Equation (13) gives the melting enthalpy DHm =
79.2 kJmolꢀ1 in good agreement with experimental calori-
metric
results
of
DHm =81.75 kJmolꢀ1,
DSm =
253.9 Jmolꢀ1 K, and Tm =322 K.[42] We are aware that multi-
parameter predictions along the alkane series have numer-
ous precedences,[43] but the exploitation of the standard co-
hesion free energy densities (CFED) proposed in Equa-
tion (16) provides an unexpectedly simple and rational cor-
relation between melting entropies and molecular volumes
in Equation (17), which we believe to be useful for synthetic
chemists in order to predict and tune melting temperatures
beyond the limited predictions usually obtained with the ex-
clusive resort of H/S compensation.[13] Efforts are currently
focussed on the extension of the CFED concept for the ra-
tionalization and prediction of the successive melting proc-
esses characterizing the transformation of solids into liquid
crystals and of liquid crystals into isotropic liquids.
Acknowledgements
Financial support from the Swiss National Science Foundation is grateful-
ly acknowledged.
[1] T. Engel, P. Reid, Physical Chemistry, Pearson Benjamin Cummings,
San Francisco, 2006, pp. 113–122.
Experimental Section
Solvents and starting materials: These were purchased from Strem,
Acros, Fluka AG and Aldrich and used without further purification
42,[45]
unless otherwise stated. Compounds 40,[44]
52’,0 [15] and 52’,2[15] were
,
Chem. Eur. J. 2013, 19, 8447 – 8456
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8455