“…In general, using the values of the conformational energies indicated above, the calculated result for the mean-square dipole moment of D22AC is 7.9 D 2 at 30 °C, in very good agreement with the experimental value, 7.8 D 2 , at the same temperature. Similar treatment applied to D22DAC gives 〈μ 2 〉 = 7.4 D 2 at 30 °C, also in good agreement with the experimental result, 7.6 D 2 . 5 Variation of the mean-square dipole moment of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacetate (D22AC) (continuous line) and 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl diacetate (D22DAC) (broken line) with the energies associated with gauche states about O−CH 2 bonds of the ester residue, E σ k , and about CH 2 −CH 2 bonds, E σ ‘ .…”
Section: Theoretical Analysis Of the Polarity Of The
Chains And The M...supporting
confidence: 86%
“…0.9 kcal mol -1 above that of the corresponding trans states. , As for bonds 6−9 in Figure , the rotational minima are located at 45, 135, 225, and 315°. The corresponding statistical weight matrices are − For consistency, the statistical weight matrix corresponding to the skeletal bond 10 is where σ is the statistical weight of gauche states about CH 2 −O ether bonds. Rotations of different sign about two consecutive skeletal bonds were considered negligible with the exception of those about the 3,4 and 11,12 bonds of Figure .…”
Section: Theoretical Analysis Of the Polarity Of The
Chains And The M...mentioning
The synthesis and radical polymerization of
2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl
monoacrylate are described. The values found at 50 and 60 °C for
the rate constants ratio,
k
p/k
t
1/2,
are
similar to those reported for some acrylic polymers with short side
groups at the same temperatures
although conflicting results are obtained by comparison with the
kinetic constants reported for other
similar acrylic monomers. The experimental value of the
mean-square dipole moment per repeating
unit of the resulting polymer,
poly{2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl
monoacrylate} was 7.24 D2
at 30 °C. This result is very close to the value of 7.83
D2 found, at the same temperature, for the
model
compound of the side group of the polymer,
2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacetate.
Owing
to the wide distribution of dipole moments associated with the side
groups, the dipolar correlation
coefficient of the chains was calculated by combining matricial
products of the rotational isomeric state
model and Monte Carlo techniques. The calculations suggest that
the statistics of long side groups rather
than the statistics of the main chain govern the dipolar correlation
coefficient of atactic comblike polymers.
“…In general, using the values of the conformational energies indicated above, the calculated result for the mean-square dipole moment of D22AC is 7.9 D 2 at 30 °C, in very good agreement with the experimental value, 7.8 D 2 , at the same temperature. Similar treatment applied to D22DAC gives 〈μ 2 〉 = 7.4 D 2 at 30 °C, also in good agreement with the experimental result, 7.6 D 2 . 5 Variation of the mean-square dipole moment of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacetate (D22AC) (continuous line) and 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl diacetate (D22DAC) (broken line) with the energies associated with gauche states about O−CH 2 bonds of the ester residue, E σ k , and about CH 2 −CH 2 bonds, E σ ‘ .…”
Section: Theoretical Analysis Of the Polarity Of The
Chains And The M...supporting
confidence: 86%
“…0.9 kcal mol -1 above that of the corresponding trans states. , As for bonds 6−9 in Figure , the rotational minima are located at 45, 135, 225, and 315°. The corresponding statistical weight matrices are − For consistency, the statistical weight matrix corresponding to the skeletal bond 10 is where σ is the statistical weight of gauche states about CH 2 −O ether bonds. Rotations of different sign about two consecutive skeletal bonds were considered negligible with the exception of those about the 3,4 and 11,12 bonds of Figure .…”
Section: Theoretical Analysis Of the Polarity Of The
Chains And The M...mentioning
The synthesis and radical polymerization of
2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl
monoacrylate are described. The values found at 50 and 60 °C for
the rate constants ratio,
k
p/k
t
1/2,
are
similar to those reported for some acrylic polymers with short side
groups at the same temperatures
although conflicting results are obtained by comparison with the
kinetic constants reported for other
similar acrylic monomers. The experimental value of the
mean-square dipole moment per repeating
unit of the resulting polymer,
poly{2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl
monoacrylate} was 7.24 D2
at 30 °C. This result is very close to the value of 7.83
D2 found, at the same temperature, for the
model
compound of the side group of the polymer,
2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacetate.
Owing
to the wide distribution of dipole moments associated with the side
groups, the dipolar correlation
coefficient of the chains was calculated by combining matricial
products of the rotational isomeric state
model and Monte Carlo techniques. The calculations suggest that
the statistics of long side groups rather
than the statistics of the main chain govern the dipolar correlation
coefficient of atactic comblike polymers.
“…As in the case of chemical shifts, vicinal spin coupling constants are also governed by the type and relative orientations of neighboring substituents. It has long been recognized that spin coupling constants could provide a reliable probe of conformation in flexible molecules. , Empirical expressions have been developed which relate the coupling constants to the relative geometry and electronegativity of substituents and to proton−proton dihedral angles. , These have been successfully employed to investigate conformational distributions in polymers and low molecular weight compounds . Here we are interested in observing U-shaped conformers of diesters of 2-methyl-1,3-propanediol which place the terminal groups in close proximity.…”
Proton nuclear magnetic resonance spectroscopy has been used to investigate intramolecular interactions between different aromatic groups in a series of diesters. The materials investigated comprise two aromatic groups linked by a 2-methyl-1,3-propanedioxy spacer. This spacer permits U-shaped conformations which place the two terminal aromatic groups close together, parallel in a face-to-face arrangement. For the symmetrical diesters, 1,3-bis(9-anthracenecarbonyloxy)-2-methylpropane (A2) and 1,3-bis[(3,5-dinitrobenzoyl)-oxy]-2-methylpropane (N2), neither the chemical shifts of the aromatic group protons nor the vicinal coupling constants measured in the spacer provide any evidence for a high fraction of U-shaped conformers. In both cases, the conformational distribution of the spacer is similar to that found for 1,3-diacetoxy-2-methylpropane (M2), indicating that the planar aromatic groups in A2 and N2 experience no significant mutual attractive interactions. In contrast, substantial upfield shifts are observed in the resonance frequencies of all aromatic protons in the anthacenyl and 3,5-dinitrophenyl groups of the unsymmetrical diester, 1-(9-anthracenecarbonyloxy)-3-[(3,5-dinitrobenzoyl)oxy]-2-methylpropane (AN), relative to those for the aromatic protons of the respective monoesters and symmetrical diesters. Analysis of the temperature dependence of the vicinal coupling constants indicates highly populated gauche states of the two central C-C bonds of the spacer chain, consistent with a total fraction of U-shaped conformers of about 80% at ambient temperature. Transient nuclear Overhauser effect experiments yield values of between 0.4 and 0.6 nm for average distances between protons on the dinitrophenyl ring and those on the anthracenyl ring, implying a distance of approximately 0.3 nm between the planes of the two aromatic groups. The stabilization of the U-shaped conformers in AN is rationalized in terms of quadrupole interactions between the two aromatic groups. The quadrupole moments associated with the two aromatic groups in AN have opposite sign, resulting in a significant attractive interaction when the groups are oriented face-to-face. For the symmetrical diesters, A2 and N2, the interacting aromatic groups have identical quadrupole moments and the interaction is repulsive in the face-to-face arrangement.
“…This allowed good fits to experimental data to be obtained, but the resulting values for the individual coupling constants fell considerably outside the usual range of values expected for these quantities. An alternative approach, which has been adopted by several groups − makes use of modified versions of the Karplus equation , to determine values for the conformer coupling constants, assuming fixed values for the torsion angles in each conformation. The temperature dependence of the observed couplings is then fit by varying only the conformational energies.…”
The conformational distribution of the main chain liquid crystal
polymer, poly(3-((methyltrimethylene)oxy)trimethylene
p,p‘-bibenzoate) has been studied in solution by
analysis of NMR vicinal
coupling constants and the dipole moment. Analysis of the
temperature dependence of the coupling
constants for the methylene groups adjacent to the asymmetric carbon in
the glycol spacer, measured
between −45 °C and 45 °C, yields values for the conformational
energies for each of the bonds flanking
the asymmetric carbon. Spectra recorded in deuterated chloroform
and 1,4-dioxane-d
8 yield similar
values
for the coupling constants, indicating that solvent polarity does not
significantly influence the conformational distribution. Because of uncertainty in the assignment of
NMR signals, two sets of energies
are obtained for each bond. This ambiguity is partly resolved by
analysis of the dipole moment. An
experimental value of 0.73 is obtained for the dipolar correlation
coefficient, g, in dioxane at 30 °C, which
is consistent with energies E
σβ = 0.5 ±
0.3 kJ mol-1 and
E
σα = −1.3 ± 0.4 kJ
mol-1 for the bond adjacent
to the ether linkage. Tentative values of
E
σα
p
= 0.0 ± 0.30
and E
σβ
p
= 1.1 ±
0.4 kJ mol-1 are obtained
for the neighboring bond attached to the ester group, based on the NMR
analysis and comparison with
conformational energies in poly(3-methyloxetane), which possesses
a similar structural unit.
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