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Hindered Rotation in Macromolecular Solids Investigated by Nuclear Magnetic Resonance.

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modified so as to open new possibilities for preparation of
derivatives of the above classes of compound which shall
have predetermined configurations.
Lecture at Hamburg (Germany) on July 12, 1968
[VB 165 IE]
German version: Angew. Chem. 80,851 (1968)
[*I Dr. M. Budnowski
Wissenschaftliche Laboratorien der Henkel & Cie GmbH
4 Diisseldorf 1, Postfach 1100 (Germany)
vNyo+
y CH2-CH-CH,
I
I
C1
1
OH C1
x >> 6
’<
Hindered Rotation in Macromolecular Solids,
Investigated by Nuclear Magnetic Resonance
(3)
(a), R’ = RZ = H, R3 = CHz-CHOH-CH2C1
(b). R’ = H, R2 = R3 = CHZ-CHOH-CHZCl
(c), R’ = R2 =
R3 = C H ~ - C H O H - C H ~ C i
(d), R’ = R2 = CHz-CHOH-CH2C1,
R3 = C
H
2
~
0
(e), R’ = R~ = CH~T.
0
R3 = CH2-CHOH-CH2CI
(f),R’ = R2 = R3 = CH
2T
By R. KosfeldC*l
Nuclear magnetic resonance and nuclear magnetic relaxation
are used as well as the mechanical-dynamic and dielectric
methods for the study of molecular movements and their
relation with the structure of amorphous and semicrystalline
macromolecular solids.
The evaluation of investigations of this type are based on the
fact that thermal molecular motion always occurs above
absolute zero. These transpositions are strongly temperaturedependent. Owing to the complicated structure of high polymers, different types of movement can take place simultaneously or (depending on the temperature) successively. Thus
at low temperatures, smaller groups such as the CH3 group
are the first to exhibit recognizable mobility. With increasing
temperature larger parts of the molecule become mobile, and
the micro-Brownian movement begins only above the glass
temperature Tg.
We studied the freezing-in of the rotation of CH3 groups in
polycarbonate (PC) and poly-or-methylstyrene (PMSt).
Whereas the planar rotation of the CH3 groups in PC die
down between 216 and 64 “K, the rotation of the CH3 groups
in PMSt freezes at temperatures between 320 and 80 OK.
r N H
A = 0-Aryl. S-Aryl. S-Alkyl. NRz
Partial hydrolysis degrades the products ( 4 ) to the urea
derivatives ( 6 ) , a 4 4 ) giving a mixture of two isomers (6). but
@ ( 4 ) giving only one urea derivative (6). namely that formed
in lower yield from or-(4).
Total hydrolysis of ( 4 ) . ( 5 ) . and (6) leads to l-amino-2propanol derivatives (71, independently of the isomer (4)
or (6) used. Acylation of (7) with urea regenerates both
isomers (6) in approximately equal yield.
These results identify or-(3f) and @-(3f) as racemates with
the configurations (R,R,S/S,S,R) and (R,R,R/S,S,S) at
the asymmetric centers. The ring-opening reactions, which
occur with complete retention, require the same assignments
of configuration for the adducts ( 4 ) . For a - ( 4 ) the three
possibilities of ring fission lead to two moles of (R,S)-meso
and one mole of (R,S/S,S)-racemic urea derivative (6). @ - ( 4 )
can give only one racemate for ( 6 ) . Synthesis of ( 6 ) from
racemic (7) and urea yields the rneso-(4) and the rac-(4)
in about equal amounts.
Since the product distribution found for the diastereoisomers
approximates to that calculated statistically, intramolecular
interaction of the chiral groups is probably small. By variation of the anion in the reactant HA, this method can be
If a classical jump process is assumed for the rotation of the
CH3 groups, the activation energies for rotation as found
from N M R measurements are 1.2 kcal.mole-1 for P C and
1.5 kcal.mole-1 for PMSt. The limiting frequencies for this
process would then be in the MHz range, i.e. they would be
too low by a factor of 106.
Another model discussed instead of classical movement for
the CH3 groups is a quantum-mechanical rotator with a
three-fold axis of symmetry, which can overcome the potential opposing rotation by the tunnel effect. This model gives
a low-temperature potential barrier of 5.4-5.5 kcal.mole-1
for both polymers. At higher temperatures, the values of the
correlation frequencies vC, which are equal to the tunnel
frequencies for the quantum-mechanical rotator, differ considerably from those expected from the quantum-mechanical
model. This is understandable, in view of the fact that the
neighboring groups, which are responsible for the hindrance
of the CH3 rotation, also become more mobile with rising
temperature. As the temperature rises, therefore, the rotation
of the methyl groups approximate more closely to a rotation
diffusion capable of being described in the classical theory.
This result shows that the movement behavior of the methyl
groups on transition from the frozen-in to the “freely mobile”
state cannot be described merely by the model of a quantummechanical rotator, and points to a correlation spectrum.
Angew. Chem. internat. Edit.
1 Vol. 7 (1968) 1 No.
10
Correlation functions are very difficult to determine. The
amount N M E of frozen CH3 groups in relation to the total
number N M was determined as a function of the temperature
by separation of the nuclear magnetic absorption curve.
Hence it is possible to calculate the number of methyl groups
that pass from the frozen state into rotational motion
as a result of a temperature increase 6T for PC and PMSt.
[l] H. L. Hodgkin and A . F. Huxley, I. Physiology 117, 500
(1952).
[2] G. Adam, Z. Naturforsch. 236, 181 (1968).
[ 3 ] K. S . Cole and J . W. Moore, J. gen. Physlol. 4 4 , 123 (1960).
[41 I . Tasaki, I. Singer, and K. Takenaka, J. gen. Physiol. 48,
1095 (1965).
It is thus possible, from the nuclear magnetic resonance experiment, to find the number of CH3 groups that are forced
by a temperature change 6 T from a rotational movement
below vc to a rotational movement above vC. This number is
related to the number of CH3 groups found in a frequency
range 6, around a frequency vC that is fixed by the temperature.
High-pressure Properties and
Structure of Liquids
[VB 166 1El
Lecture at Hamburg (Germany) on June 14, 1968
German version: Angew. Chem. 80, 851 (1968)
~
.-
~
[ * ] Doz. Dr. R. Kosfeld
Institut fur Physikalische Chemie der
Technischen Hochschule
51 Aachen, Templergraben 59 (Germany)
Electrical Excitation of the Axon Membrane as
Co-operative Ion Exchange
By G. Adcim [*I
The widely accepted theory proposed by Hodgkin and
Huxleyril for nerve stimulation fails to explain the mechanism of regulation of the state of the axon membrane by the
membrane potential or the cation activities.
If, on the other hand, the axon membrane is regarded as a
two-dimensional cation exchanger interacting with the internal and external electrolyte reservoirs, a physico-chemical
mechanism can be advanced for the control of the electrical
state of the membranef21. In this mechanism, calcium ions
are bound in the lattice sites of the cation exchanger in the
resting state. On depolarization or on lowering of the calcium
activity in the outside medium, the resting state becomes
thermodynamically unstable, and calcium is co-operatively
displaced from the lattice sites by monovalent cations. The
movements of the ions during this cation exchange give rise
to an ion current flowing inward, as observed e.g. in the
voltage-clamp experiment.
This co-operative cation exchange is described as a twodimensional phase transition. Its kinetics can be theoretically
described for small depolarizations o n the basis of the concept of nucleation and nuclear growth.
The resulting kinetic theory has been applied to the. measurements of Cole and Moore[3Jof the ion current in the voltage
clamp experiment. Within the range of validity of the theory,
i.e. for small depolarizations, the experimentally determined
dependence of the ion current on time and on the membrane
potential, particularly the threshold behavior that characterizes axon stimulation, is quantitatively described by the
equations derived.
Three parameters must be matched. Two of these have simple
molecular meanings, and ha;e the following numerical
values: a, = 21 x 21 .&2 = area per binding site for the cooperatively exchangeable cations; w = 5.1 kcal/mole = interaction energy between two binding sites in the two different
bonding states.
It is probable, from the order of magnitude of these parameters, that the structural units responsible for the axon stimulation are membrane-bound proteins, as was suggested by
Tasaki e f al. [ 4 J .
Lecture a t Konstanz (Germany) on June 27, 1968
[ V B 167 IE]
German version: Angew. Chem. 80, 806 (1968)
[*] Dr. G. Adam
Institut fur Physiologische Chemie der Universitdt
8 Miinchen 15, Goethestrasse 33 (Germany)
Angew. Chem. internat. Edit.
Yo!. 7 (1968) No. I0
By E. Kuss[*I
In contrast to solids, compressed gases and liquids can be
studied at pressures up to 10 kbar over a wide range of densities and hence valuable information about the intermolecular
forces and the structure of liquids, which is still largely unknown,can be obtained from the physical properties. Properties
of interest in this connection are the pVT data, the equations of
state, the thermal conductivity, the viscosity, the spin-lattice
interaction of the nuclear magnetic resonance, and the electric birefringence.
The theoretical calculation of the second, third fourth, and
higher virial coefficients from fundamental potential functions leads to very complicated mathematical expressions and
in some cases to very different constants for the potential
functions. Owing to the mathematical difficulties, the potential U(r) is always taken to be spherically symmetrical, i.e.
the effect of the shape of the molecule is not yet theoretically
expressible.
The effect of the molecular structure on the pVT data of
liquids has been studied experimentally up to 2000 atm, and
in some cases even up to 5000 atm. A piezometric method
and a buoyancy method have been developed for this purpose. Since no suitable material was available for use as a
float, the test substance was introduced into a hollow body
and the buoyancy was measured in mercury. Measurements
that have not yet been completed show that some substances
whose viscosities are extremely pressure-dependent have a
very low compressibility (e.g. 2,4-bis-(l-phenylethyl)methoxybenzene).
The viscosity measurements were carried out in a falling
sphere viscometer (accuracy & 2 yo)and a capillary viscometer
(accuracy f 1 yo),both of which are suitable for fully automatic operation. The effects of chain length, “degree of
branching”, and other parameters of the molecular structure
on the viscosity-pressure behavior were determined for
numerous substances. On the basis of the relationships found,
it was possible to synthesize substances whose viscosities at
2000 atm are up to 8 x 106 times as great as a t atmospheric
pressure [I]. According to Benedek and PurceN[21, a comparison of measurements of the pressure-dependence of the
viscosity and the nuclear magnetic relaxation leads to the
conclusion that the translational degrees of freedom are more
strongly reduced than the rotational degrees of freedom by
rising pressure.
The very small measured effect in the electric birefringence
requires the complete elimination of parasite birefringence
of the high pressure windows in high-pressure measurements.
Benzene showed a marked anomaly in the pressure dependence of the Kerr constant [31, which suggests a modification
of the r-electron cloud or an unusual change in the liquid
structure under pressure.
[VB 170 IE]
Lecture a t Berlin (Germany) on July 5, 1968
German version: Angew. Chem. 80, 806 (1968)
[“I Prof. Dr. E. Kuss
Institut fur Erdolforschung der Technischen Hochschule
3 Hannover, Am kleinen Felde 30 (Germany)
111 E. Kuss, Chemie-1ng.-Techn. 37, 465 (1965); Angew. Chem.
internat. Edit. 4 , 944 (1965).
[21 G. B. Benedek and E. M . Purcell, J. chern. Physics 22, 2003
(1954).
[3] E. Kuss and H. H. Heydemann, Z. physik. Chem. N.F. 43,
91 (1964).
829
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