Computing Handedness
J. Am. Chem. Soc., Vol. 123, No. 26, 2001 6261
and Br2 in CCl4, followed by hydrogenation of (R)-(+)-â-citronellol
4. Experimental Section
(7) (Fluka, [R]24 ) +4.46° (neat), 97.4% ee).
D
4.1. Measurements. CD and UV absorption spectra were recorded
simultaneously on a JASCO J-720 spectropolarimeter equipped with a
liquid nitrogen-controlled quartz cell with path length of 5 mm in a
cryostat, ranging from 23 to -90 °C, and a Peltier-controlled quartz
cell with path length of 10 mm, ranging from 80 to -10 °C. Detailed
measurement conditions have already described in the literature.11 The
sample concentration was 2 × 10-5 (Si-repeat unit)-1 dm-3 for UV
and CD measurements. 13C (75.43 MHz) and 29Si (59.59 MHz) NMR
spectra were taken in CDCl3 at 30 °C with a Varian Unity 300 NMR
spectrometer using tetramethylsilane as an internal standard. Optical
rotation at the Na-D line was measured with a JASCO DIP-370
polarimeter using a quartz cell with path length of 10 mm at room
temperature (24 °C). The weight-average molecular weight (Mw) and
number-average molecular weight (Mn) of the polymers were evaluated
using gel permeation chromatography (Shimadzu A10 instruments,
Shodex KF806M as a column, and HPLC-grade tetrahydrofuran as
eluent at 30 °C), based on a calibration with polystyrene standards.
The enantiopurity of starting materials and intermediates were
determined at Toray Research Center (TRC, Shiga, Japan) using the
chiral gas chromatography technique (Spelco, â-DEX-325 and â-DEX-
225, 30 m × 0.25 mm ID, column oven temperature 70-95 °C, He
carrier with 1.2 mL/min). Detailed analytical conditions were â-DEX-
325 at 70 °C for 4 and 9, â-DEX-225 at 82 °C for 6 and 10, and â-DEX-
225 at 90 °C for 7 and 11 (see in section 4.3.). We concluded that the
enantiopurities of 4, 6, 7, 9, 10, 11 used in this work were sufficiently
high with almost identical ee’s. However, the chiral GC analysis at
the TRC indicated that the enantiopurity of (S)-(-)-â-3,7-citronellol
Filtration of the reaction mixture and vacuum distillation of the
filtrate afforded pure 1. Colorless liquid. Yield 9.8 g (42%); bp 108-
113°/0.20 mmHg, [R]24 ) +3.18° (neat). 29Si NMR (CDCl3, 30 °C,
D
ppm) 34.73, 13C NMR (CDCl3, 30 °C, ppm) 11.33, 17.38, 18.64, 22.63,
22.72, 24.76, 27.99, 28.70, 28.73, 29.14, 34.81, 36.44, 36.48, 39.32.
(S)-(+)-3,7-Dimethyloctyl-(S)-3-methylpentyldichlorosilane (8) was
synthesized in a similar way using (S)-3,7-dimethyloctylbromide (9,
[R]24 ) +6.05° (neat), 95.0% ee) (Chemical Soft) from (S)-(-)-3,7-
D
dimethyloctanol (10, [R]24 ) -4.22° (neat), 95.9% ee) and (S)-(-)-
D
â-citronellol (11, Fluka, [R]24D ) -4.55° (neat), 97.4% ee) as starting
material. Colorless liquid; bp 109-113°/0.20 mmHg, [R]24D ) +5.60°
(neat). 29Si NMR (CDCl3, 30 °C, ppm) 34.75, 13C NMR (CDCl3, 30
°C, ppm) 11.32, 17.37, 18.64, 19.11, 22.63, 22.71, 24.75, 27.98, 28.70,
29.14, 34.80, 36.44, 36.47, 39.31.
4.4. Polymer Preparation. A typical synthetic procedure is described
as follows for PS-1. To a mixture of 12 mL of dry toluene (Kanto),
0.50 g (22 mmol) of sodium (Wako), and 0.06 g (0.23 mmol) of 18-
crown-6 (Wako), 1.6 g (4.9 mmol) of 1 was added dropwise in an
argon atmosphere. The mixture was stirred slowly at 110 °C. After 2
h, 150 mL of dry toluene was added to reduce solution viscosity and
stirring was continued for a further 30 min. The hot reaction mixture
slurry was passed immediately through a 5-µm PTFE filter under argon
gas pressure. To the clear filtrate, 2-propanol and ethanol as precipitating
solvents were added carefully. Several portions of white precipitates
were collected by centrifugation and dried at 120 °C under vacuum
overnight.
For PS-1, high-molecular weight (HMW) fraction: Mw ) 5.83 ×
106 (DPw ) ca. 23 000) and Mn ) 3.44 × 106; low-molecular weight
(LMW) fraction: Mw ) 7.36 × 104 (DPw ) ca. 290) and Mn ) 2.47
× 104; for PS-2, HMW fraction, Mw ) 4.67 × 106 (DPw ) ca. 18 400)
and Mn ) 2.09 × 106, LMW fraction, Mw ) 6.37 × 104 (DPw ) ca.
250) and Mn ) 23400. 29Si NMR (CDCl3, 20 °C, ppm); for PS-1 (LMW
fraction): -25.32; for PS-2 (LMW fraction): -25.69, 13C NMR (CDCl3,
20 °C, ppm, major peaks); for PS-1 (LMW fraction):11.95, 17.38,
18.77, 22.57, 22.75, 25.58, 28.11, 28.70, 28.73, 29.14, 34.81, 36.86,
36.48, 39.39; for PS-2 (LMW fraction, major peaks): 11.91,19.00,
22.56, 22.74, 25.58, 28.13, 29.06, 35.34, 37.18, 38.51, 39.36.
(Merck, [R]24 ) -3.11° (neat), corresponding to 68.4% ee based on
D
[R]24D of purer 11 by Fluka) was only 64.8% ee, and also (S)-(-)-3,7-
dimethyloctanol (Chemical Soft (Kyoto, Japan), based on the Merck
product) was 66.4% ee. On the basis of the analysis, we used 7(Fluka)
and 11 (Fluka) only as starting materials.
4.2. Molecular Mechanics Calculations. Molecular mechanics
calculation was performed using the Molecular Simulation Inc., the
Discover 3 module, Ver. 4.00 on Silicon Graphics Indigo II XZ based
on standard default parameters with a Si-Si bond length of 2.34 Å
and a Si-Si-Si bond angle of 111° using the MSI pcff force field
suitable for polymers. For this calculation, the MSI built-in function
of simple-minimize (default: dihedral angle restraints, the steepest
descents with the first derivative for 1.0, iteration limit 1000, movement
limit 0.2, followed the conjugate gradients) and simple-dynamics
(default: constant volume and constant temperature, initial temperature
300 K, time step 1 fs, velocity Verlet integration method, initial velocity
is random from Boltzman distribution) were used.
Initially, after an oligomer model (31 repeating units terminated with
hydrogen) with dihedral angle of 180° was generated, two oligomer
models with dihedral angle of 150° and 210° were preliminarily
generated. Next, calculation of P-screw-sense oligomer model setup
with desired dihedral angle was carried out based on the 150°-model,
and M-models were based on the 210°-model, respectively.
Acknowledgment. We thank Hiromi Tamoto-Takigawa for
preliminary CD and UV measurements. Drs. Masao Morita, Kei-
ichi Torimitsu, and Hideaki Takayanagi are gratefully acknowl-
edged for their continuing support. Professors Takahiro Sato,
Junji Watanabe, Masashi Kunitake, Shoji Furukawa, and Eiji
Yashima are acknowledged for fruitful comments and discus-
sion. Drs. Zhong-Biao Zhang and Hongzhi Tang are acknowl-
edged for discussion. Correspondence and requests for material
and Supporting Information should be addressed to M.F.
(e-mail: fujiki@will.brl.ntt.co.jp).
4.3. Monomer Preparation. The synthetic procedure for (R)-(+)-
3,7-dimethyloctyl-(S)-3-methylpentyldichlorosilane (1) is described. (S)-
3-Methylpentyltrichlorosilane (2) was obtained by coupling 68 g (0.40
mol) of tetrachlorosilane (Shin-Etsu) with the Grignard reagent formed
from 29.5 g (0.25 mol) of (S)-(+)-3-methylpentyl chloride (3) (Chemical
Soft). Colorless liquid. Yield 33.3 g (76%); bp 70-73°/6.5 mmHg,
Supporting Information Available: Variable temperature
UV and CD spectra of PS-1 (HMW fraction) in isooctane at
-80, -40, -20, -10, -8, -5, 0, 5, 10, 25, 55, and 80 °C,
variable temperature UV and CD spectra of PS-2 (HMW
fraction) in isooctane at -83, -61, -40, -19, -5, 0, 25, 55,
and 80 °C, variable temperature gabs values of PS-1 (HMW and
LMW fractions) and PS-2 (HMW fraction), which are normal-
ized by the regression gabs curve of PS-4, and schematic
illustration of twisting and translational motions of helical motifs
and helix reversals (PDF). This material is available free of
[R]24 ) +2.25° (neat). 29Si NMR (CDCl3, 30 °C) 13.66 ppm, 13C
D
NMR (CDCl3, 30 °C, ppm) 19.00, 21.66, 22.61, 22.70, 24.67, 27.95,
28.93, 34.38, 36.39, 39.24. Dichlorosilane 1 was obtained by slowly
adding Grignard reagent (5) obtained from 33 g (0.15 mol) of (R)-(-
)-3,7-dimethyloctylbromide (4, [R]24 ) -5.96° (neat), 96.6% ee) to
D
17.4 g (79 mmol) of 2 in dry diethyl ether at room temperature. The
bromide 4 was prepared at Chemical Soft by bromination of (R)-(+)-
3,7-dimethyloctanol (6, [R]24 ) +3.90° (neat), 95.7% ee) with PPh3
JA0026509
D