4826 J . Org. Chem., Vol. 61, No. 14, 1996
Notes
Ta ble 3. Com p etition Da ta for th e Rea ction of
Sch em e 5
P er flu or o-6-br om o-4-oxa -1-h exen e, 4, w ith n -Bu 3GeH a t
303 Ka
[bromide]
[n-Bu3GeH]
[5]/[6]
yield, %
0.052
0.052
0.052
0.052
0.052
0.052
0.41
0.52
0.62
0.69
0.74
0.82
2.71
3.07
3.57
3.88
4.10
4.49
98
98
96
97
97
99
Ta ble 2. Com p etition Da ta for th e Rea ction of
P er flu or o-n -h ep tyl Ra d ica l w ith 1-Hexen e a n d
Tr ibu tylger m a n iu m Hyd r id e a t 303 Ka
a
Computed slope ) kH/kC ) 4.38 ( 0.11.
[1-hexene]
[Bu3GeH]/[1-hexene]
8/9
yield, %
in which appropriate amounts of n-Bu3GeH had been charged.
Six of such samples, varied in the amounts of n-Bu3GeH (Table
3), were needed to complete the rate determination. Samples
were sealed in NMR tubes by rubber septa, degassed (freeze and
thaw) three times under argon, and then photolyzed using a
Rayonet reactor for 10 min (monitored by 19F NMR) at room
temperature. The products (reduced 5 and cyclized 6) of the
reactions were quantitatively analyzed by 19F NMR. PhCF3 was
used as the internal standard to calculate the NMR yield of the
reactions. The ratios of reduced 5 to cyclized 6 were obtained
by measuring the integrals of the corresponding peaks in the
19F NMR (CF2H, δ -137.26 for 5; CF2H, δ -139.26 for 6). The
ratios of 5:6 were obtained for varied concentrations of n-Bu3-
GeH, which were then combined with the respective concentra-
tions of the reductant to allow the determination of the ratio
kH/kC.
1.76
1.51
1.26
1.01
0.75
0.58
0.31
0.44
0.63
0.90
1.37
1.97
0.74
0.97
1.31
1.79
2.66
3.94
94
96
99
99
100
97
a
Computed slope ) kH/kadd ) 2.42 ( 0.05.
would appear that a better model system to examine from
that respect would be radical 9. The generation and
cyclizations of radicals such as 9 are currently under
investigation.
Exp er im en ta l Section
1,1,2,2,3,3-Hexaflu or o-3-br om opr opyl tr iflu or ovin yl eth er ,
4: 19F NMR (282 MHz, CDCl3, CFCl3), δ -64.28 (s, 2F), -83.77
(s 2F), -113.39 (d of d, J ) 83 Hz, 65 Hz, 1F), -121.20 (s, 2F),
-121.62 (d of d, J ) 112 Hz, 83 Hz, 1F), -135.11 ppm (d of d, J
) 112 Hz, 66 Hz, 1F); HRMS, calcd for C5F9OBr, 325.8989,
found, 325.9018.
Ma ter ia ls. Perfluoro-n-heptyl iodide was obtained com-
mercially (PCR, Inc.) and used as received. Tributylgermanium
hydride was prepared by the reaction of n-Bu3GeCl with Li-
AlH4.21 1,1,2,2,3,3-Hexafluoro-3-bromopropyl trifluorovinyl ether
(4) was provided by the CR & D Department of DuPont, and no
further purification of the sample was needed. Both 1-H-
perfluoro-n-heptane, 7, and 1-n-hexylperfluoro-n-heptane, 8, had
been prepared and characterized in earlier work.2 All com-
pounds used in this work were >96% pure, as determined by
1H NMR and analytical gas chromatography (SE-30), and all
products were purified by preparative gas chromatography using
P r ep a r a tion of 1,1,2,2,3,3-Hexa flu or op r op yl Tr iflu or ovi-
n yl Eth er , 5, a n d 2-(d iflu or om eth yl)p er flu or o-1-oxa cyclo-
p en ta n e, 6. The title compounds were prepared from the
bromide 4. To 0.55 mL of tributylgermanium hydride with 0.5
mL of degassed benzene in a Pyrex NMR tube was added 0.27
mL (1.59 mmol) of 4. The mixture was photolyzed in a Rayonet
reactor for 10 min. 19F NMR analysis indicated that the reaction
was finished. Through preparative GC (SE-30), the title com-
pounds were isolated in a purity of >96%.
a
1/4 × 10 ft SE-30 column.
P r oced u r e for Deter m in a tion of th e Ra te Con sta n t for
H-a tom Tr a n sfer (kH) to th e P er flu or o-n -h ep tyl Ra d ica l
fr om Tr i-n -bu tylger m a n iu m Hyd r id e. Reaction samples
were prepared by adding 8 µL of radical precursor (perfluoro-
n-heptyl iodide) to benzene-d6 in a Pyrex NMR tube into which
appropriate amounts of Bu3GeH21 and 1-hexene were charged.
Six such samples, varied in the amounts of Bu3GeH and
1-hexene (Table 2), were needed to carry out the rate determi-
nation. Each reaction mixture was degassed (freeze and thaw)
three times and sealed with rubber septa under argon in a Pyrex
NMR tube and then photolyzed using a Rayonet reactor for 4 h
to complete its reactions (monitored by 19F NMR). The amounts
of products (reduction 7 and addition 8) were quantitatively
determined by 19F NMR. PhCF3 was used as the internal
standard to calculate the NMR yield of each reaction. The ratios
of reduced product 7 to addition product 8 were obtained by
measuring the integral of the corresponding peaks in the 19F
NMR (CF2-H, δ -138.1 for 7; CF2-CH2, δ -114.4 for 8).2 These
ratios of 7/8, obtained for varied concentrations and ratios of
1-hexene and tri-n-butylgermanium hydride, permitted the
determination of the ratio, kH/kadd, using the equation given in
the discussion section.
1,1,2,2,3,3-Hexa flu or op r op yl tr iflu or ovin yl eth er , 5: 1H
NMR (300 M Hz, CDCl3, TMS), δ 6.04 (t of t, J ) 52 Hz, 5 Hz,
1H); 19F NMR (282 M Hz, CDCl3, CFCl3), δ -86.56 (s, 2F),
-113.08 (d of d, J ) 83 Hz, 68 Hz, 1F), -121.45 (d of d, J ) 110
Hz, 81 Hz, 1F), 132.44 (s, 2F), -134.71 (d of d, J ) 112 Hz, 66
Hz, 1F), -137.26 ppm (m of d, J ) 58 Hz, 2F); HRMS, calcd for
C5HF9O, 247.9884, found, 247.9888.
2-(Diflu or om eth yl)p er flu or o-1-oxa cyclop en ta n e, 6: 1H
NMR (300 MHz, CDCl3, TMS), δ 6.03 (d of t, J ) 52 Hz, 7 Hz,
1H); 19F NMR (282 MHz, CDCl3, CFCl3), δ -82.89 (d, J ) 8 Hz,
1F), -82.99 (t, J ) 7 Hz, 1F), -126.18 (d, J ) 127 Hz, 1F),
-129.16 (d of d, J ) 262 Hz, 7 Hz, 1F), -131.63 (d, J ) 262 Hz,
1F), -131.38 (s, 1F), -133.40 (m of d, J ) 312 Hz, 1F), -135.43
(m of d, J ) 250 Hz, 1F), -139.26 ppm (d of d, J ) 312 Hz, 52
Hz, 1F); HRMS, calcd for C5HF9O, 247.9884, found, 247.9872.
Ack n ow led gm en t. Support of this research in part
by the National Science Foundation and by DuPont is
gratefully acknowledged.
P r oced u r e for Deter m in a tion of th e Ra te Con sta n t (kC)
for th e In tr a m olecu la r Cycliza tion of th e P er flu or o-4-oxa -
5-h exen yl Ra d ica l, 2. Reaction samples were made by adding
10 µL of radical precursor 4 to benzene-d6 in a Pyrex NMR tube
Su p p or tin g In for m a tion Ava ila ble: 1H and 19F NMR of
5 and 6 (4 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
(21) Stang, P. J .; White, M. R. J . Am. Chem. Soc. 1981, 103, 5429-
5433.
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