H. Martinez et al. / Journal of Fluorine Chemistry 135 (2012) 167–175
175
nucleophile. The rate-enhancing effect of fluorine substituents on
E2 reactions appears to be largely due to their C–H acidifying
influence, which derives from two factors: their aforementioned
inductive effect, and when geometry allows, their powerful
to the NMR tube. The reaction was then followed by measurement
of the decrease of one particular NMR signal with respect to the
internal standard up to 30% of the reaction. For kinetic experiments
above room temperature, 0.22 mmol of substrate in 0.25 mL of
deuterated solvent were placed into an NMR tube, and then
0.75 mL of the corresponding 0.6 M stock solution and 5–10 mg of
internal standard were added. The NMR tube was warmed to the
desired temperature and the reaction followed by NMR up to 30%
of the reaction.
hyperconjugative stabilization of developing
b-negative charge.
4. Experimental
4.1. Synthesis of 1-bromo-1-fluorononane (6) [9]
In the following order 170 mL of anhydrous CH2Cl2, 5.1 mL
(28.1 mmol, 1 equiv., 95%) of nonanal and 3.9 mL (33.7 mmol,
1.2 equiv.) of 2,6-lutidine were placed into a 250 mL round
bottomed flask. The mixture was then cooled down to ꢃ5 8C
and 9.5 mL (56.2 mmol, 2 equiv.) of triflic anhydride in 20 mL of
anhydrous CH2Cl2 were added dropwise to the reaction mixture
over a period of 45 min. The reaction was stirred for 7 h at 0 8C and
was then placed in the refrigerator (0 8C) for an extra 17 h. The
relatively dilute nonanal solution, the presence of the base and the
slow addition of triflic anhydride were important in order to obtain
good yield in this reaction; otherwise a polymer is obtained as a
major product. The solvent was removed and the dark remaining
mixture was extracted with pentane (4 ꢂ 100 mL). The polymer is
insoluble in pentane. The organic layer was washed with aqueous
HCl 1.2 M (2 ꢂ 100 mL), followed by concentrated aqueous
NaHCO3 (2 ꢂ 100 mL) and then brine (1 ꢂ 100 mL). The solution
was dried over MgSO4, filtered, and the solvent removed to give a
dark yellow oil, 9.5 g, 80% yield of the geminal, bis-triflate (by
NMR). This material was used without further purification for the
following step. Once the solvent is removed, the product should be
kept in the refrigerator, since it not stable neat at room
temperature.
4.2.2. Computational methods
The quantum chemical calculations were performed with a
hybrid basis set at MP2/6-31+G(d,p)-LANL2DZ level of theory. The
effective core potential (ECP) of iodide was included in the
calculations in order to minimize the time in the optimization.
DMSO was used as a solvent in all calculations using the
polarizable continuum model (PCM). The transition states were
characterized by one and only one negative frequency and the
intrinsic reaction coordinate (IRC) connecting both the starting
material and the product. All the calculations were performed
using Gaussian 03 Rev. E01 Software package [23].
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
References
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The bis-triflate (9.5 g, 22.5 mmol, 1 equiv.) along with 150 mL
of anhydrous CH2Cl2 were placed in a 250 mL round bottomed
flask. The mixture was then cooled to 0 8C, and 22.5 mL of TBAF 1 M
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fluorononane (6) and 12% 1,1-difluorononane, which was used for
the kinetic experiments as is.
6: 1H NMR (CDCl3)
d
6.36–6.53 (dt, 2JHF = 50.7 Hz, 3JHH = 5.3 Hz,
1H, CHF), 2.00–2.45 (m, 2H, CH2), 1.20–1.75 (m, 14H, CH2), 0.89 (t,
2
3H, CH3); 19F NMR (CDCl3)
d
ꢃ130.65 (ddd, JHF = 50.3 Hz,
3JHF = 20.5 Hz, JHF = 18.2 Hz, 1F); 13C NMR (CDCl3)
d 95.9 (d,
3
1JCF = 252.5 Hz, CHF), 40.9 (d, JCF = 18.7 Hz, CH2), 32.02 (CH2),
29.56 (CH2), 29.33 (CH2), 28.91 (CH2), 25.30 (CH2), 22.86 (CH2),
14.29 (CH3); HRMS: Calc. 223.0503 ((MꢃH)+). Found 223.0489).
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2
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4.2. 1-Octyl tosylate was prepared according to the literature [8]. It’s
NMR spectra were consistent with those in the literature [25]
4.2.1. General procedure for the kinetic experiments
Stock solutions of NaN3, NaOMe and NaI (0.6 M in MeOH-d4 and
DMSO-d6) were prepared prior to the kinetics experiments. For
kinetic experiments below room temperature, 0.75 mL of the
required 0.6 M stock solution, and 5–10 mg of internal standard
(toluene for 1H NMR and trifluorotoluene for 19F NMR) were placed
into an NMR tube and the tube cooled to the desired temperature
inside the NMR instrument. Then, 0.22 mmol of substrate
previously dissolved in 0.25 mL of deuterated solvent were added
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