A structure conformation analysis of three new lariat crown ethers based on theory and experiment

Article abstract of DOI:10.1016/j.molstruc.2004.06.005

Three new lariat crown ethers (LCEs) were synthesized. Their structures were determined by NMR spectroscopy, mass spectroscopy, and X-ray crystallography. The methoxybenzyl sidearms of c-pivot LCEs of methoxy group are located at ortho, meta, and para position, respectively. The three LCEs are found to be structural isomers. The observed X-ray crystal structures of the 2-methoxybenzyl sym-dibenzo-16-crown-5 ether showed three important conformational isomers that are stable conformations not commonly seen in X-ray crystallography. An experimental study and a theoretical analysis using the B3LYP/6-31G* method in the GAUSSIAN 98 package program were conducted on the three new 16-crown-5 ethers. Molecular mechanics and density functions were used in the theoretical study to determine the relative geometric stabilities of the three isomers. Optimal geometric structures of these compounds were also determined. The calculated molecular mechanics compared quite well with those obtained from X-ray crystallography. The ionization potentials, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, energy gaps, heat of formation, atomization energies, and vibration frequencies of the compounds were also calculated. The results of the calculations show that these new ethers are stable molecules with high reactivity and various other physical properties. The study of these 2-, 3-, 4-methoxybenzyl sym-dibenzo-16-crown-5 ethers also provided a better understanding of the conformational properties of macrocyclic ligands.

Full text of DOI:10.1016/j.molstruc.2004.06.005

Journal of Molecular Structure 702 (2004) 23–31
www.elsevier.com/locate/molstruc
A structure conformation analysis of three new lariat crown
ethers based on theory and experiment
Chia-Ching Sua, Li-Hwa Lub,
*
aDepartment of Applied Science, Chinese Naval Academy, 669 Jiun Shiaw Road, Kaohsiung 813, Taiwan, ROC
bDepartment of General Education, The Fooyin University, Ta-Liao, Kaohsiung 831, Taiwan, ROC
Received 28 April 2004; revised 31 May 2004; accepted 2 June 2004
Available online 6 July 2004
Abstract
Three new lariat crown ethers (LCEs) were synthesized. Their structures were determined by NMR spectroscopy, mass spectroscopy, and
X-ray crystallography. The methoxybenzyl sidearms of c-pivot LCEs of methoxy group are located at ortho, meta, and para position,
respectively. The three LCEs are found to be structural isomers. The observed X-ray crystal structures of the 2-methoxybenzyl sym-dibenzo-
16-crown-5 ether showed three important conformational isomers that are stable conformations not commonly seen in X-ray crystallography.
An experimental study and a theoretical analysis using the B3LYP/6-31G* method in the GAUSSIAN 98 package program were conducted on
the three new 16-crown-5 ethers. Molecular mechanics and density functions were used in the theoretical study to determine the relative
geometric stabilities of the three isomers. Optimal geometric structures of these compounds were also determined. The calculated molecular
mechanics compared quite well with those obtained from X-ray crystallography. The ionization potentials, highest occupied molecular
orbital energy, lowest unoccupied molecular orbital energy, energy gaps, heat of formation, atomization energies, and vibration frequencies
of the compounds were also calculated. The results of the calculations show that these new ethers are stable molecules with high reactivity
and various other physical properties. The study of these 2-, 3-, 4-methoxybenzyl sym-dibenzo-16-crown-5 ethers also provided a better
understanding of the conformational properties of macrocyclic ligands.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Lariat crown ether; B3LYP; 6-31G*; HOMO and LUMO energies; Energy gaps
1. Introduction
upon the diameters of the ions and the site of the interactions
(charge–dipole, dipole–dipole). Conformational study of
crown ether in both solution and solid phases has become an
area of considerable research recently.
The first macrocyclic polyethers were reported by
Lu¨ttringhaus in 1937 as part of an investigation of medium-
and large-sized rings [1]. Since Pederson [2] reported the
formation of stable complexes between macrocyclic poly-
ethers and salts of alkali and alkaline earth metals in 1967,
many crown ethers have been synthesized and extensively
studied. Current interest in the clinical use of chelating
agents as vehicles for delivery of metals to sites in
biological systems has led to the synthesis and study of a
large number of new cyclic polyoxa and polyaza ligands.
Crown ethers are multidentate ligands that exhibit selectiv-
ity over specific metal ions in solutions containing other
chemically similar ions. The binding between a cation and a
macrocyclic ligand has been shown to exhibit high
selectivity [3–15]. The binding of the cations depends
Using macrocyclic ligands containing oxygen, nitrogen
and sulfur atoms, studies to understand molecular confor-
mation have been extensively performed by both exper-
imental and theoretical approaches [16–20]. Knowledge of
the conformational preference of crownophanes is essential
for predicting their three-dimensional structures and binding
affinities with guest molecules, given that the size fit and
directionality are very important for molecular recognition.
Through the cooperation of crown ring and side arm, lariat
crown ethers (LCEs) often exhibit different cation-binding
properties when comparing with their parent crown ethers
[21–23]. Because the functional groups of sidearm LCEs
are key components in the formation of metal–crown ether
complexes and in molecular recognition [21,24], detailed
information about the conformational energies of LCE is
*
Corresponding author. Tel.: þ886-7-786-2844; fax: þ886-7-786-2841.
E-mail address: xx412@mail.fy.edu.tw (L.-H. Lu).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.06.005

24
C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
important for the understanding of the binding affinities of
the crownophanes with guest molecules and for the design
of artificial host molecules.
temperature. 2-Methoxybenzyl chloride (0.68 ml, 5 mmol)
and NaH (1.0 g, 25 mmol) were added and the reaction
mixture was refluxed for a further 3 h. Deionized water
was slowly added to the mixture to destroy the excess
NaH and terminate the reaction. After purification by
column chromatography (silica gel, 70–230 mesh, CHCl3
as eluent), the desired product 1 was obtained in 80%
(1.86 g) yield, m.p. 96.0–97.0 8C. MS (EI, 70 eV): m/z
466(Mþz, 29%), 330 (31%), 286 (13.4%), 181 (14%), 147
(24%), 136 (45%), 121 (100%), 77 (23%). Elemental
analysis: Calcd (found) for C27H30O7: C, 69.51 (69.45);
Scientific studies using theoretical calculations have
become more important in recently years. In fact,
theoretical and experimental studies are to be closely
linked. Without theoretical studies, experimental results
alone cannot yield methods to allow systematic analyses.
Without experimental studies, the accuracy of theoretical
studies cannot be proven. The two studies are therefore to
supplement each other. In the past decade, theoretical
studies have gradually become the mainstream of
chemical research. It provides scientists with a tool to
explain experimental phenomenon. In addition, chemical
calculations also provide assistance in the prediction of
unknown chemical phenomenon. It can also provide a
basis for experimental design.
1
H, 6.48 (6.40), H NMR (CDCl3): d 3.83 (S, 3H, OCH3),
3.94 (m, 4H, OCH2CH2OCH2CH2O), 4.17 (m, 3H,
OCH H0CHCH H0, 4H, OCH2CH2OCH2CH2O), 4.32
(m, 2H, OCHH0CHCHH0), 4.91 (S, 2H, CH2PhOCH3),
6.87–7.00 (m, 10H, benzo group), 7.28 (t, 1H, benzo
group), 7.53 (d, 1H, benzo group).
Recently reported calculations of organic molecules
[25–48] have shown that, the B3LYP method in the
GAUSSIAN 98 package program together with the 6-31G*
basis set function (BSF) of the density function theory
(DFT) can be a useful tool in providing sufficiently accurate
conformational analysis [49]. One of the objectives of this
research is to determine the conformational composition of
each isomer of concern. The research included using the
B3LYP/6-31G* method to conduct calculations for the
determination of relative geometric structures, molecular
orbital energy, and other thermodynamic properties of three
structural isomers of LECs. The three structural isomers
were selected to check for the accuracy of theoretical
analysis versus experimental results. The research is also to
help understand the effect of the binding between a cation
and LCEs on high selectivity so as to explain the
conformational changes.
2.3. Synthesis of 3-methoxybenzyl sym-dibenzo-16-crown-5
ether (2)
1.73 g (5 mmol) of hydroxy-sym-dibenzo-16-crown-5
ether was dissolved in 50 ml of anhydrous THF. 0.8 g
(20 mmol) of NaH was then added under nitrogen. The
reaction mixture was heated under reflux for 30–40 min.
Next, 3-methoxybenzyl chloride (5 mmol) was added to this
solution. Heating was continued under reflux for 1 h. The
excess NaH was destroyed with water and the reaction
mixture was purified as descrbed in 1 to give 2 in 80%
(1.86 g) yield, m.p. 93.0–94.0 8C. MS (EI, 70 eV): m/z 466
(Mþz, 15%), 286 (3%), 256 (3%), 181 (3%), 149 (10%), 136
(20%), 121 (100%), 107 (10%), 91 (21%). Elemental
analysis: Calcd (found) for C27H30O7: C, 69.51 (69.15);
1
H, 6.48 (6.54), H NMR (CDCl3): d 3.82 (S, 3H, OCH3),
3.93 (m, 4H, OCH2CH2OCH2CH2O), 4.16 (m, 3H,
OCH H0CHCHCH H0O; 4H, OCH2CH2OCH2CH2O), 4.31
(m, 2H, OCHH0CHCHH0), 4.89 (S, 2H, CH2PhOCH3),
6.87–7.00 (m, 11H, benzo group), 7.36 (t, 1H, benzo
group).
2. Experimental details
2.1. Reagents and chemicals
All chemicals used for the synthesis were of available
purity and were used without any further purification.
Only analytical reagent grade chemicals were used in
the preparation of the three new LCEs. The hydroxy-
sym-dibenzo-16-crown-5 ether was synthesized [50]
and used after recrystallization from chloroform–hexane
(1:5, V:V).
2.4. Synthesis of 4-methoxybenzyl sym-dibenzo-16-crown-5
ether (3)
1.73 g (5 mmol) of hydroxy-sym-dibenzo-16-crown-5
ether was dissolved in 50 ml of anhydrous THF. 0.8 g
(20 mmol) of NaH was then added under nitrogen. The
reaction mixture was heated under reflux for 30–40 min.
Next, 4-methoxybenzyl chloride (5 mmol) was added to
this solution. Heating was continued under reflux for 1 h.
The excess NaH was destroyed with water and the
reaction mixture was purified as descrbed in 1 to give 3 in
81% (1.89 g) yield, m.p. 72.0–73.0 8C. MS (EI, 70 eV):
m/z 466 (Mþz, 12%), 286 (4%), 149 (8%), 136 (20%), 121
(100%), 107 (9%), 91 (18%). Elemental analysis: Calcd
(found) for C27H30O7: C, 69.51 (69.26); H, 6.48 (6.41),
1H NMR (CDCl3): d 3.81 (S, 3H, OCH3), 3.93 (m, 4H,
2.2. Synthesis of 2-methoxybenzyl sym-dibenzo-16-crown-5
ether (1)
1.73 g (5 mmol) of hydroxy-sym-dibenzo-16-crown-5
ether was dissolved in 50 ml of anhydrous THF. 0.4 g
(10 mmol) of sodium hydride (NaH) was then added
under nitrogen. The reaction mixture was heated
under reflux for 30–40 min and then cooled to room

C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
25
OCH2CH2OCH2CH2O), 4.16 (m, 3H, OCH H0CHCH H0;
the geometric optimization calculations. The objective is
to accurately calculate the properties of the five different
major geometric structures of 1–3.
4H,
OCH2CH2OCH2CH2O),
4.31
(m,
2H,
OCHH0CHCHH0), 4.82 (S, 2H, CH2PhOCH3), 6.84–7.00
(m, 10H, benzo group), 7.36 (d, 2H, benzo group).
3.2. Geometric optimization
2.5. Production of single crystals of the three
new 16-crown-5 ethers
The results of the calculations were used to verify the
reasonableness of the input coordinate data. If unreason-
able data were used, either the geometric symmetry of
the molecules would be destroyed or unusual bond length
or bond angle would be produced. Any of these errors
would result in the termination of the calculations. It was
found that the calculations could achieve convergence
much easier if the input data were closer to the
experimental values of the minimal energy points of
the molecules. By starting the calculations using the
standard bond length and bond angle, the completion and
convergence of the self-consistent field calculations can
be achieved in fewer steps. The converged calculations
Single crystals of the three LCEs were produced by
recrystallization followed by a crystal-growing process.
The recrystallization involved heating the three 16-crown-
5 ethers together with proper amount of n-hexane.
Chloroform was then slowly added to the mixture until
the compound was fully dissolved. Magnesium sulfate
was then added and the mixture was filtered while still
hot. The filtered product was then put into a crystal-
growing bottle. The n-hexane vapor was used to slowly
diffuse the product until a perfect crystal was produced.
The structure of the resulting single crystals was then
analyzed by X-ray crystallography. Data were collected
using a Nonius CAD-4 diffractometer with graphite-
monochromate Mo Ka radiation at 25 8C. Atomic scatter-
ing factors were taken from the International Tables for
X-ray Crystallography, and data reduction and structural
refinement were performed using NRCVAX packages.
Cell parameters were obtained from 25 reflections with 2u
at 20.74–27.22, 9.42–21.46, and 18.72–22.928,
respectively.
3. Computational method
3.1. Calculation methods and input
All the calculations were performed using the B3LYP
method included in the GAUSSIAN 98 package software
together with the 6-31G* BSF of the DFT [49]. The
values obtained from the X-ray structural analysis were
used as initial coordinates in the input to the calculation.
The standard bond length, bond angle, and related atomic
van der waals radius were selected as starting point to
Fig. 2. ORTEP diagram of three conformational isomers of lariat crown
ether 1.
Fig. 1. Structure of three new lariat crown ethers.

26
C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
vibration frequency, ionization energy, energy gap between
HOMO and LUMO, atomic heat, enthalpy and Gibbs
energy, etc. of each geometric isomer were calculated. The
results were then used to determine the relative stability of
the three structural isomers. The resulting molecular
stability and conductivity are of special importance and
value.
4. Results and discussions
4.1. Geometric structure
The obtained geometric structure of three new c-pivot
LCEs is shown in Fig. 1. Through structural analysis using
X-ray crystallography, the ORTEP diagrams of the three
major structural isomers were also identified, as shown in
Figs. 2–4. The 2-methoxybenzyl sym-dibenzo-16-crown-5
Fig. 3. ORTEP diagram of lariat crown ether 2.
Table 1
Crystallographic data and optimized structure of lariat crown ether 1
˚
located using B3LYP/6-31G* calculations for atomic bond lengths (A)
can then provide the optimal geometric bond length,
bond angle and dihedral angle of the three geometric
isomers.
Atomic bond Crystallographic data
lengths
B3LYP/6-31G*
1a 1b 1c
1a
1b
1c
3.3. Orbital field energy, vibration frequency, and
thermodynamic properties
O1–C1
1.380(40) 1.393(24) 1.411(22) 1.418 1.418 1.419
1.390(30) 1.364(23) 1.390(30) 1.372 1.371 1.375
1.313(20) 1.421(17) 1.425(17) 1.431 1.433 1.422
1.426(15) 1.424(15) 1.426(16) 1.422 1.423 1.420
1.417(16) 1.405(15) 1.408(18) 1.420 1.421 1.429
1.341(17) 1.390(15) 1.352(19) 1.364 1.364 1.370
1.362(18) 1.348(17) 1.353(19) 1.364 1.364 1.375
1.430(18) 1.431(16) 1.312(24) 1.418 1.418 1.435
1.387(18) 1.418(18) 1.392(22) 1.413 1.413 1.422
1.410(18) 1.397(17) 1.415(19) 1.412 1.412 1.418
1.430(17) 1.445(17) 1.448(17) 1.420 1.420 1.430
1.383(17) 1.371(20) 1.360(18) 1.366 1.366 1.371
1.375(16) 1.383(18) 1.402(17) 1.375 1.375 1.376
1.436(18) 1.438(16) 1.442(17) 1.440 1.439 1.431
1.350(30) 1.370(30) 1.390(30) 1.400 1.401 1.396
1.340(30) 1.424(22) 1.410(30) 1.409 1.409 1.409
1.390(40) 1.370(40) 1.400(50) 1.397 1.396 1.399
1.390(30) 1.390(30) 1.360(40) 1.393 1.393 1.391
1.380(40) 1.319(24) 1.370(30) 1.396 1.395 1.399
1.390(30) 1.354(24) 1.380(30) 1.395 1.396 1.392
1.460(30) 1.476(20) 1.472(22) 1.511 1.510 1.511
1.527(18) 1.539(17) 1.498(19) 1.532 1.532 1.539
1.513(19) 1.520(18) 1.483(19) 1.527 1.526 1.531
1.381(21) 1.395(19) 1.352(22) 1.392 1.392 1.399
1.401(20) 1.364(19) 1.408(22) 1.417 1.417 1.414
1.412(22) 1.385(20) 1.379(21) 1.402 1.402 1.398
1.312(22) 1.366(21) 1.347(23) 1.388 1.389 1.392
1.405(23) 1.403(21) 1.391(22) 1.402 1.402 1.397
1.380(22) 1.390(19) 1.385(22) 1.393 1.393 1.393
1.475(22) 1.456(20) 1.450(30) 1.516 1.516 1.524
1.465(20) 1.477(20) 1.487(20) 1.515 1.515 1.527
1.365(21) 1.393(22) 1.376(21) 1.398 1.399 1.399
1.386(19) 1.374(22) 1.400(21) 1.413 1.413 1.415
1.371(23) 1.390(23) 1.397(22) 1.399 1.399 1.399
1.347(23) 1.329(24) 1.351(22) 1.392 1.392 1.391
1.395(22) 1.406(25) 1.396(22) 1.398 1.399 1.397
1.409(20) 1.356(23) 1.364(20) 1.392 1.392 1.392
O1–C2
O2–C8
O2–C9
Using the optimal solutions of the geometric calcu-
lations, thermodynamic properties of orbital energy,
O3–C10
O3–C11
O4–C16
O4–C17
O5–C18
O5–C19
O6–C20
O6–C21
O7–C26
O7–C27
C2–C3
C2–C7
C3–C4
C4–C5
C5–C6
C6–C7
C7–C8
C9–C10
C9–C27
C11–C12
C11–C16
C12–C13
C13–C14
C14–C15
C15–C16
C17–C18
C19–C20
C21–C22
C21–C26
C22–C23
C23–C24
C24–C25
C25–C26
Fig. 4. ORTEP diagram of lariat crown ether 3.

C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
27
Table 2
Table 3
Crystallographic data and optimized structure of lariat crown
ether 2 located using B3LYP/6-31G* calculations for atomic bond
Crystallographic data and optimized structure of lariat crown ether 3
˚
located using B3LYP/6-31G* calculations for atomic bond lengths (A)
˚
lengths (A)
Atomic bond lengths
Crystallographic data
B3LYP/6-31G*
Atomic bond lengths
Crystallographic data
B3LYP/6-31G*
O1–C1
1.421(5)
1.361(5)
1.398(5)
1.397(5)
1.445(6)
1.381(6)
1.380(6)
1.446(5)
1.422(5)
1.416(5)
1.416(6)
1.361(5)
1.378(6)
1.385(6)
1.384(5)
1.374(6)
1.370(6)
1.387(6)
1.349(7)
1.504(6)
1.377(6)
1.497(7)
1.537(7)
1.380(8)
1.372(7)
1.401(10)
1.356(10)
1.367(8)
1.377(7)
1.486(6)
1.488(6)
1.385(7)
1.370 (7)
1.363(8)
1.370(11)
1.363(10)
1.380(6)
1.417
1.367
1.428
1.423
1.438
1.376
1.366
1.421
1.412
1.413
1.418
1.363
1.364
1.420
1.401
1.400
1.390
1.402
1.400
1.509
1.397
1.526
1.532
1.392
1.413
1.398
1.391
1.399
1.399
1.515
1.516
1.393
1.417
1.402
1.388
1.402
1.392
O1–C1
1.410(9)
1.350(8)
1.436(7)
1.421(6)
1.416(6)
1.374(7)
1.366(7)
1.413(7)
1.408(8)
1.416(8)
1.430(7)
1.367(7)
1.388(7)
1.422(7)
1.384(10)
1.383(9)
1.363(11)
1.401(10)
1.394(9)
1.351(8)
1.504(8)
1.516(8)
1.501(8)
1.366(9)
1.395(8)
1.395(10)
1.370(11)
1.384(10)
1.382(9)
1.497(9)
1.495(10)
1.386(9)
1.383(8)
1.395(10)
1.340(10)
1.383(10)
1.391(9)
1.417
1.368
1.423
1.424
1.420
1.364
1.364
1.418
1.413
1.412
1.420
1.366
1.376
1.438
1.399
1.403
1.399
1.390
1.404
1.392
1.512
1.531
1.526
1.392
1.417
1.402
1.389
1.402
1.393
1.516
1.515
1.398
1.413
1.399
1.392
1.398
1.391
O1–C2
O1–C2
O2–C8
O2–C8
O2–C9
O2–C9
O3–C10
O3–C11
O4–C16
O4–C17
O5–C18
O5–C19
O6–C20
O6–C21
O7–C26
O7–C27
C2–C3
O3–C10
O3–C11
O4–C16
O4–C17
O5–C18
O5–C19
O6–C20
O6–C21
O7–C26
O7–C27
C2–C3
C2–C7
C2–C7
C3–C4
C3–C4
C4–C5
C4–C5
C5–C6
C5–C6
C5–C8
C6–C7
C6–C7
C6–C8
C9–C10
C9–C27
C11–C12
C11–C16
C12–C13
C13–C14
C14–C15
C15–C16
C17–C18
C19–C20
C21–C22
C21–C26
C22–C23
C23–C24
C24–C25
C25–C26
C9–C10
C9–C27
C11–C12
C11–C16
C12–C13
C13–C14
C14–C15
C15–C16
C17–C18
C19–C20
C21–C22
C21–C26
C22–C23
C23–C24
C24–C25
C25–C26
These tables show that both the bond lengths and torsion
angles, obtained from the theoretical calculations, are
consistent with those from experimental investigations
using X-ray crystallography.
ether (1) showed three conformational isomers simul-
taneously. The structures of the three structural isomers
show different crystal systems and space groups. As
described earlier [49], the coordinates of the X-ray
structural analysis were used as input data to compare
the reliability and reasonableness of the theoretical
methods used in this research. The AM 1 semi-empirical
method was first used to conduct calculations until
convergence was achieved. The geometric optimization
was then conducted using the 6-31G* BSF and the B3LYP
method. Tables 1–3 provide the resulting bond lengths of
the three major structural isomers from the X-ray crystal-
lography structural analysis and theoretical calculations.
Similarly, Tables 4–6 provide the torsion angles obtained
using the X-ray crystallography structural analysis
and theoretical calculations. In addition, Table 7 provides
the crystallographic data collected during the study.
4.2. Molecular first ionization potentials, HOMO
and LUMO energies, energy gaps
Table 8 lists the calculated values of the first
ionization potentials, HOMO, LUMO, and energy gap
ðD1HOMO–LUMOÞ of the three major structural isomers of
the LCEs. The first ionization potential 1 of 1b was
found to be the lowest. On the other hand, the energy
gap of structural isomer 2 was found to be the lowest,
indicating higher conductivity. Table 8 also shows that
1c has both the highest first ionization potential and the
highest energy gap.

28
C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
Table 4
Table 5
Crystallographic data and optimized structure of lariat crown ether 1
located using B3LYP/6-31G* calculations of atomic torsion angle
(degrees)
Crystallographic data and optimized structure of lariat crown ether 2
located using B3LYP/6-31G* calculations of atomic torsion angle
(degrees)
Atomic torsion Crystallographic data
angle
B3LYP/6-31G*
1a 1b 1c
Atomic torsion angle
Crystallographic data
B3LYP/6-31G*
1a
1b
1c
C1–O1–C2
118.5(6)
113.3(4)
118.4(4)
118.8(4)
112.5(5)
117.2(5)
113.7(4)
124.0(6)
117.1(6)
118.9(6)
119.3(6)
122.4(7)
116.9(6)
120.7(6)
117.4(5)
121.9(6)
121.8(6)
108.3(5)
106.4(4)
112.0(5)
110.0(5)
105.8(4)
124.8(5)
114.4(5)
120.8(5)
120.1(6)
118.8(6)
121.7(6)
119.3(6)
115.0(5)
125.8(5)
119.2(6)
107.5(5)
108.6(5)
108.9(6)
108.5(5)
124.8(5)
115.8(5)
119.4(6)
119.2(6)
121.4(7)
120.2(7)
119.7(6)
121.7(5)
118.2(5)
120.1(6)
108.9(5)
118.2
115.1
119.1
118.9
113.1
118.5
116.0
124.5
115.3
120.2
119.0
121.0
119.9
119.5
119.5
121.0
120.5
110.2
105.4
111.4
111.5
107.5
125.2
115.1
119.8
120.2
120.1
120.1
120.2
115.0
125.4
119.6
107.3
109.0
109.3
108.3
124.8
115.9
119.3
120.2
120.5
119.5
120.7
121.0
119.1
119.9
107.9
C8–O2–C9
C1–O1–C2
C8–O2–C9
121.1(20) 118.6(16) 118.9(15) 118.6 118.6 118.6
117.6(11) 114.0(10) 118.4(10) 115.4 115.1 117.0
C10–O3–C11
C16–O4–C17
C18–O5–C19
C20–O6–C21
C26–O7–C27
O1–C2–C3
C10–O3–C11 117.5(10) 119.0(9)
119.5(11) 118.8 119.0 119.3
C16–O4–C17 118.7(11) 117.2(10) 123.9(13) 118.9 118.9 118.9
C18–O5–C19 113.3(11) 115.5(10) 113.9(12) 113.1 113.1 114.3
C20–O6–C21 116.8(10) 118.6(11) 117.8(10) 118.4 118.5 118.5
C26–O7–C27 115.9(10) 113.5(10) 116.6(10) 116.1 116.0 116.4
O1–C2–C7
O1–C2–C3
O1–C2–C7
C3–C2–C7
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C7
C2–C7–C6
C2–C7–C8
C6–C7–C8
O2–C8–C7
O2–C9–C10
O2–C9–C27
117.0(21) 124.8(16) 120.7(19) 123.6 123.4 124.2
117.4(18) 115.5(16) 118.6(16) 116.0 116.3 115.0
125.5(21) 119.6(17) 120.6(22) 120.4 120.3 120.8
117.6(18) 119.5(17) 118.5(21) 119.8 119.9 119.5
120.0(17) 120.7(16) 119.6(18) 120.4 120.5 120.4
118.5(19) 118.4(16) 122.7(22) 119.3 119.1 119.7
121.7(18) 124.6(16) 119.0(19) 121.6 121.7 121.0
116.6(18) 117.0(14) 119.4(16) 118.5 118.4 118.6
121.4(22) 120.6(15) 114.4(17) 120.8 121.6 118.6
121.9(21) 122.3(14) 126.0(15) 120.7 120.0 122.8
114.7(16) 111.6(12) 106.6(12) 108.6 108.3 109.4
106.5(10) 105.8(10) 110.6(10) 104.4 104.8 112.3
112.3(11) 111.8(10) 118.2(11) 112.3 112.0 114.4
C3–C2–C7
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C7
C5–C6–C8
C7–C6–C8
C2–C7–C6
O2–C8–C6
O2–C9–C10
O2–C9–C27
C10–C9–C27
O3–C10–C9
O3–C11–C12
O3–C11–C16
C12–C11–C16
C11–C12–C13
C12–C13–C14
C13–C14–C15
C14–C15–C16
O4–C16–C11
O4–C16–C15
C11–C16–C15
O4–C17–C18
O5–C18–C17
O5–C19–C20
O6–C20–C19
O6–C21–C22
O6–C21–C26
C22–C21–C26
C21–C22–C23
C22–C23–C24
C23–C24–C25
C24–C25–C26
O7–C26–C21
O7–C26–C25
C21–C26–C25
O7–C27–C9
C10–C9–C27 111.6(11) 110.3910) 113.0(11) 111.3 111.3 112.0
O3–C10–C9 105.9(10) 106.8(10) 107.8(11) 108.1 108.0 110.5
O3–C11–C12 125.9(13) 122.0(11) 129.4(14) 125.1 125.1 124.6
O3–C11–C16 113.8(12) 115.4(11) 111.9(13) 115.2 115.2 116.3
C12–C11–C16 120.3(14) 122.7(12) 118.7(14) 119.7 119.7 119.1
C11–C12–C13 117.7(13) 117.8(12) 122.8(14) 120.2 120.2 120.4
C12–C13–C14 122.3(14) 120.5(14) 119.3(14) 120.1 120.1 120.5
C13–C14–C15 120.8(15) 120.9(13) 119.9(14) 120.1 120.1 119.3
C14–C15–C16 118.9(14) 119.0(12) 121.0(14) 120.3 120.2 120.9
O4–C16–C11 116.5(12) 116.3(11) 117.1(13) 115.0 115.0 119.9
O4–C16–C15 123.6(13) 124.7(12) 124.6(14) 125.4 125.4 120.2
C11–C16–C15 119.9(14) 119.0(13) 118.3(14) 119.6 119.6 119.7
O4–C17–C18 108.3(12) 108.0(11) 112.2(16) 107.3 107.3 108.6
O5–C18–C17 112.8(13) 110.7(11) 113.3(15) 109.0 109.0 108.6
O5–C19–C20 111.2(12) 113.5(12) 109.7(11) 109.3 109.3 115.0
O6–C20–C19 108.2(11) 107.2(11) 105.1(11) 108.3 108.3 109.6
O6–C21–C22 124.0(12) 123.9(14) 124.7(13) 124.8 124.9 124.2
O6–C21–C26 114.3(12) 116.0(14) 116.8(13) 115.9 115.8 116.7
C22–C21–C26 121.6(13) 120.0(15) 118.5(14) 119.3 119.3 119.1
C21–C22–C23 117.6(14) 117.8(14) 119.0(14) 120.2 120.2 120.5
C22–C23–C24 123.8(15) 123.2(15) 122.6(14) 120.5 120.5 120.4
C23–C24–C25 118.9(14) 117.7(16) 118.5(14) 119.5 119.5 119.3
C24–C25–C26 118.9(13) 121.4(15) 120.0(14) 120.7 120.6 121.1
O7–C26–C21 122.7(12) 121.3(13) 120.2(12) 121.1 121.0 122.2
O7–C26–C25 118.2(12) 118.7(13) 118.1(13) 119.0 119.1 118.1
C21–C26–C25 119.0(13) 119.8(15) 121.5(14) 119.8 119.9 119.6
O7–C27–C9
108.9(11) 107.1(10) 106.1(11) 108.2 108.1 107.7
about the relative stabilities of the three structural isomers.
In general, the formation of the three LCEs are exothermic
ðDH , 0Þ and also causes LCEs to be more rigid, which is
probably the reason that the entropy change for the reaction
is slightly negative. However, the change in the enthalpy is
big and negative enough to overcome the negative change of
entropy. These calculated results show lower atomization
enthalpy and Gibbs energy of atomization. They also show
4.3. Thermal properties (DHf; DGf ; Ha; Ga)
Table 9 provides the calculated thermal properties of the
three structural isomers of LCE, including enthalpy of
formation ðDHfÞ; Gibbs energy of formation ðDGfÞ; enthalpy
of atomization ðDHaÞ; and Gibbs energy of atomization
ðDGaÞ: These thermodynamic data provide information

C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
29
Table 6
Table 7
Crystallographic data and optimized structure of lariat crown ether 3
located using B3LYP/6-31G* calculations of atomic torsion angle
(degrees)
Crystallographic data
1
2
3
Atomic torsion angle
Crystallographic data
B3LYP/6-31G*
Empirical formula
Formula weight
Crystal system
Space group
C
27H30O7
C27H30O7
466.53
C27H30O7
466.53
466.53
C1–O1–C2
116.0(3)
116.2(3)
112.6(3)
118.1(4)
112.6(3)
119.0(4)
117.9(4)
116.9(3)
123.8(3)
119.3(4)
120.6(4)
119.7(4)
119.2(4)
119.8(5)
120.9(5)
121.9(4)
119.2(4)
106.4(3)
113.8(4)
102.5(4)
108.4(4)
109.4(4)
120.1(5)
120.6(5)
119.3(5)
120.1(6)
119.6(6)
120.4(6)
120.5(6)
116.2(4)
123.6(5)
120.2(5)
107.4(3)
106.7(3)
106.8(3)
107.0(4)
124.6(5)
116.7(4)
118.8(4)
120.9(7)
119.6(6)
120.6(5)
119.7(6)
115.0(3)
124.6(5)
120.4(5)
108.9(4)
118.1
115.3
115.8
118.3
113.2
119.1
119.2
115.8
124.7
119.5
120.0
121.2
118.1
120.6
121.3
121.4
119.7
109.4
111.9
105.3
111.2
108.1
119.1
121.0
119.8
120.8
119.4
120.5
120.3
116.0
124.8
119.2
108.4
109.2
108.9
107.2
125.5
114.9
119.6
120.2
120.1
120.1
120.2
115.0
125.2
119.8
107.6
Monoclinic
P2(1)/C
Orthohombic
Pcab
Orthohombic
C8–O2–C9
P2(1)2(1)2(1)
C10–O3–C11
C16–O4–C17
C18–O5–C19
C20–O6–C21
C26–O7–C27
O1–C2–C3
˚
Unit cell dimensions (A)
a
b
c
17.823(4)
17.532(10)
24.752(5)
9.781(3)
18.627(2)
26.842(3)
7.411(2)
16.779(4)
19.723(7)
b (degrees)
110.3
7254(5)
12
90.0
90.0
3
˚
O1–C2–C7
Volume (A )
4890(2)
8
2452(1)
4
C3–C2–C7
Z (atoms/unit cell)
calc (mg m23
C2–C3–C4
D
)
1.282
0.09
1.267
0.09
1.264
0.09
Mu (mm21
)
C3–C4–C5
C4–C5–C6
F (000)
2976
1984
992
C4–C5–C8
Range of 2u (degrees)
Crystal size (mm3)
49.8
51.8
51.8
C6–C5–C8
0.50 £ 0.15
£ 0.08
0.35 £ 0.15
£ 0.08
0.60 £ 0.50
£ 0.50
C5–C6–C7
C2–C7–C6
Octants measured
O2–C8–C5
h
k
l
221 to 19
0–20
0–12
0–22
0–33
0–9
O2–C9–C10
O2–C9–C27
C10–C9–C27
O3–C10–C9
O3–C11–C12
O3–C11–C16
C12–C11–C16
C11–C12–C13
C12–C13–C14
C13–C14–C15
C14–C15–C16
O4–C16–C11
O4–C16–C15
C11–C16–C15
O4–C17–C18
O5–C18–C17
O5–C19–C20
O6–C20–C19
O6–C21–C22
O6–C21–C26
C22–C21–C26
C21–C22–C23
C22–C23–C24
C23–C24–C25
C24–C25–C26
O7–C26–C21
O7–C26–C25
C21–C26–C25
O7–C27–C9
0–20
0–24
0–29
Number of unique
reflection
12,704
13,025
2781
4777
4777
1734
2742
2742
1833
Number of reflections
measured
Number of reflections
with I . 2sðIÞ
Number of variables
Absorption correction
Rf
635
248
307
0.892–0.965
0.070
0.904–0.955
0.058
0.818–0.975
0.056
Rw
0.070
0.054
0.049
GoF
0.929
0.955
1.305
located at the minimal points of the potential energy
surfaces, indicating that all five different isomers are very
stable molecules. The calculated maximum frequencies are
between 3261.003 and 3452.523 cm21 for the three new
LCEs. Among the calculated values, structural isomer 1 of
the conformational isomer 1a is found to have the lowest
frequency (10.201 cm21).
Table 8
Comparison of HOMO, LUMO, energy gaps ðD1HOMO–LUMOÞ; and first
ionization potentials of the three LCEs including the three geometric
isomers (eV)
that the five different isomers are stable and easy-to-form
molecules with high reactivities. Calculations indicate that
1c is formed most readily and is also the most stable.
Parameter
Molecule
1a
1b
1c
2
3
4.4. Vibration frequencies
1HOMO
1LUMO
I1st
25.4159 25.4039 25.7413 25.4420 25.4515
0.0879 20.0049
5.4159
5.3280
0.0297
5.7413
5.7116
0.2356
5.4420
5.2064
0.1635
5.4515
5.2880
5.4039
5.4088
The calculated vibration frequencies of the five different
isomers are all positive, indicating that these molecules are
D1HOMO–LUMO

30
C.-C. Su, L.-H. Lu / Journal of Molecular Structure 702 (2004) 23–31
Table 9
different complex ability between LCEs and metals will
result.
Comparison of calculated thermal properties of the three LCEs including
the three geometric isomers (298 K, kcal mol21
)
This research was performed to investigate the
conformational preferences of the three new LCEs that
can be used as building blocks of the LCE macrocycles.
The results of this research of high-density, high-energy
LCEs should provide contribution to the material science
and other related fields. This research also shows that
chemical calculations can be an important tool in
scientific study. Accurate theoretical calculations can
help identify experimental errors and their ranges, and
also provide ways to obtain important chemical and
physical information that cannot be easily obtained by
experimental approaches.
Para- Molecule
meter
1a
1b
1c
2
3
DHf
DGf
23369.469 23362.791 23372.009 23368.653 23368.367
23055.507 23043.778 23056.335 23055.263 23055.046
DHa 7.12233
DGa 6.247865
7.111688
6.229175
7.126378
6.249185
7.121031
6.247477
7.120575
6.247131
5. Conclusions
Three new LCEs were synthesized and their structures
were determined by X-ray crystallography. In the field of X-
ray structural analysis, the finding that LCE 1 has three
different conformational isomers co-existing stably is hardly
seen. Through theoretical calculations using the B3LYP/6-
31G* density function method, data of the three structural
isomers were successfully obtained. From these calculated
and analytical results, the following conclusions can be
drawn.
Acknowledgements
The helpful suggestions from Professor L. Liu-Kao and
Operator T. S.Kuo of National Taiwan Normal University,
Department of Chemistry, are greatly appreciated. The
authors also thank the National Science Council of the
Republic of China (Taiwan) for its financial support (NSC
90-2113-M-145-001). Dr Y.C. Su, P.E., of Houston, TX,
USA, is also greatly appreciated for a critical reading of this
manuscript prior to publication.
(1) The calculated bond lengths and torsion angles of
the three structural isomers are very close to the
experimental values and are quite reasonable. These
results prove that the calculations of geometric
structures of these molecules were successful.
(2) Through the calculations of the first ionization
potentials, HOMO, LUMO, and energy gaps, it was
found that the three structural isomers have low energy
gaps between the first ionization potentials
and HOMO. The electrons on the outermost molecular
orbital are therefore easily lost, indicating higher
conductivity.
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