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13C NMR spectrum of pentafluorobutane
Research notes
P:bs
2296
=
These expressionsare identical indicating that both methods yield the same results for all solid angles. Furthermore, the expressionsare identical with expression 7 in [l] which is to say that either method available in the 180’ mode is as accurate as the most accurate method available in the 90° mode. Figure 2 shows the form of the departure from the ideal of pobsfor a band whose value of Pide*lequals 0.75. For oriented single crystal studies, GILSONhas pointed out an important advantage to be gained by using the 180’ scattering arrangement[3]. This arisesbecause both incident and scattered light are subject (ideally) to the same section of the optical indicatrix thus simplifying birefiingence considerations. PETERDAWSON
Depmtment of Physics King’s College Strand, London. W.C.2 [3] T. R. GILSON and P. J. HENDRA,her
Ramun
&WCtTO8COpy,
Wiley-Interscience (1970).
SpectrochimicaActs, Vol. 28A, pp. 2296 to 2297. PergamonPreea1972. Printed in NorthernIreland
lsC14811R spedrum of pentafluorobutane (Received 3 Augud
1971)
Abstract-From the “C n.m.r. spectrum of pentafluorobutane the C-H and C-F coupling constants have been determined and some regular trends have been observed and discussed.
of coupling constants between ‘aC and rBF has been based in the past on the observation of 1% satellites in isF spectra. However the advent of modern spectrometersoffers now the considerableadvantage of easy measuringthese couplingsdirectly from the lsC spectra which makes possible the observation of long range couplings otherwise difficult to measure. Since only one paper [I] has been published in this field, dealing more with aromatic molecules, we think worthwhileto report on the resultsobtained for 1,1,1,3,3-pentalluorobutane. Considering its particularstructurethis compound providesthe possibilityof simultaneousmeasurements of couplings CH and CF respectively of nuclei situated in comparable positions. KNOWGEDUE
EXPERIB~ENTAL Spectra were measured on the neat liquid, in 10 mm tubes, using an HFX-90 Bruker spectrometer operating at a frequency of 22.62 MHz, equipped with broad band decoupler and the 1070 Fabritek computer of average transients. Hetero nuclearlock was based on the singlet of C,F,. The temperature of the sample during broad-band decoupling was about 40-50% due to the high irradiating power level. Number of scans varied from 100 to 500, sweep time was from 80 to 160 set/scan. As an example of the proton decoupled spectra the CH, and CH, absorptions are reported in Figs. 1 and 2. Couplings C-H were measured in the undecoupled spectra. All the measured parameters are collected in Table 1. [l] F. J. WEIQERTand J. D. ROBERTS,J. Am. Chem. Sot. 98, 2361 (1971).
2296
Fig. 1. One of the central components of CH, quartet,
Fig. 2. Central component of CH, triplet. Table 1. Spectral~parametersof pentafluorobutane Carbon nucleus
Chemical* shift
SF,
123.30
CF, _CH,
118*83 21.62
CH,
Coupling con&an& in Hz with CF,
40.79
274.0 [IIt
CE, 7.2 [2]
29*4[2]
130-o [l]
3.5 [3] 1.8 [a]
5.2 [2] 1.8 [3]
* In p.p.m. from hexamethyldisyloxane. t Number of bonds between aoupled nuclei.
CE, 7.2 29.4 238.0 26.6
[3] [2] [l] [2]
CEL 2.2 5.2 130.0
c41
[3] [2] [I]
2297
Research notes DISCUSSION
The first evident feature of our results is that while lJ,H is the same in the CH, and CH, groups VCF in the CF, is considerably larger than in the CF,. ConcerningJ,, one can see that although this constant decreases by increasing the number of bonds however *J,, is still observable, while the corresponding 4J,H is not detected. This property can be used in the assignment of spectra of large fluorinated molecules. Another conclusion which can be drawn from the data is that 2JcF shows a definite dependence from the degree of substitution of the involved carbon, being larger for a secondary than for a primary carbon, while the opposite trend is observed for 2JcH: ’ JCH~-CF, _ _
J gH;-CE”r= J,,-C,, JcFrCF, = J,F,-Cg, Finally comparison (Table 2) of J,,
with J,,
< J,FS-CISS
in the same fragment for lJ, 2J, sJ shows that is
Table 2. Comparison of JHF with J,, No. of bonds
JHF
JCF
JHFiJCF (average)
1 2 3
615* 45.5~67.2* 13*2-10.2$
274238t 29.P26.6t 7.2-3.5t
2.4 1.8 2.2
* Ref. 2. t This work. $ Ref. 3. valid the empiricalrule J,, - 2 J,,. of its possible stereospecificity.
The coupling sJ,,
merits further study in consideration A. DE Maauo G. GATTI
Istituto di Chimica de& Mamnnoltxole V,ia A&n.so Cod 12 Milano, Italy [S] B. I. IONIN and B. A. ERSHOV,Plenum Press, N.Y. (1970). [3] A. DE &LSCO and G. GATTI,O.M.R. 8, 599 (1971).
P:bs
2296
=
These expressionsare identical indicating that both methods yield the same results for all solid angles. Furthermore, the expressionsare identical with expression 7 in [l] which is to say that either method available in the 180’ mode is as accurate as the most accurate method available in the 90° mode. Figure 2 shows the form of the departure from the ideal of pobsfor a band whose value of Pide*lequals 0.75. For oriented single crystal studies, GILSONhas pointed out an important advantage to be gained by using the 180’ scattering arrangement[3]. This arisesbecause both incident and scattered light are subject (ideally) to the same section of the optical indicatrix thus simplifying birefiingence considerations. PETERDAWSON
Depmtment of Physics King’s College Strand, London. W.C.2 [3] T. R. GILSON and P. J. HENDRA,her
Ramun
&WCtTO8COpy,
Wiley-Interscience (1970).
SpectrochimicaActs, Vol. 28A, pp. 2296 to 2297. PergamonPreea1972. Printed in NorthernIreland
lsC14811R spedrum of pentafluorobutane (Received 3 Augud
1971)
Abstract-From the “C n.m.r. spectrum of pentafluorobutane the C-H and C-F coupling constants have been determined and some regular trends have been observed and discussed.
of coupling constants between ‘aC and rBF has been based in the past on the observation of 1% satellites in isF spectra. However the advent of modern spectrometersoffers now the considerableadvantage of easy measuringthese couplingsdirectly from the lsC spectra which makes possible the observation of long range couplings otherwise difficult to measure. Since only one paper [I] has been published in this field, dealing more with aromatic molecules, we think worthwhileto report on the resultsobtained for 1,1,1,3,3-pentalluorobutane. Considering its particularstructurethis compound providesthe possibilityof simultaneousmeasurements of couplings CH and CF respectively of nuclei situated in comparable positions. KNOWGEDUE
EXPERIB~ENTAL Spectra were measured on the neat liquid, in 10 mm tubes, using an HFX-90 Bruker spectrometer operating at a frequency of 22.62 MHz, equipped with broad band decoupler and the 1070 Fabritek computer of average transients. Hetero nuclearlock was based on the singlet of C,F,. The temperature of the sample during broad-band decoupling was about 40-50% due to the high irradiating power level. Number of scans varied from 100 to 500, sweep time was from 80 to 160 set/scan. As an example of the proton decoupled spectra the CH, and CH, absorptions are reported in Figs. 1 and 2. Couplings C-H were measured in the undecoupled spectra. All the measured parameters are collected in Table 1. [l] F. J. WEIQERTand J. D. ROBERTS,J. Am. Chem. Sot. 98, 2361 (1971).
2296
Fig. 1. One of the central components of CH, quartet,
Fig. 2. Central component of CH, triplet. Table 1. Spectral~parametersof pentafluorobutane Carbon nucleus
Chemical* shift
SF,
123.30
CF, _CH,
118*83 21.62
CH,
Coupling con&an& in Hz with CF,
40.79
274.0 [IIt
CE, 7.2 [2]
29*4[2]
130-o [l]
3.5 [3] 1.8 [a]
5.2 [2] 1.8 [3]
* In p.p.m. from hexamethyldisyloxane. t Number of bonds between aoupled nuclei.
CE, 7.2 29.4 238.0 26.6
[3] [2] [l] [2]
CEL 2.2 5.2 130.0
c41
[3] [2] [I]
2297
Research notes DISCUSSION
The first evident feature of our results is that while lJ,H is the same in the CH, and CH, groups VCF in the CF, is considerably larger than in the CF,. ConcerningJ,, one can see that although this constant decreases by increasing the number of bonds however *J,, is still observable, while the corresponding 4J,H is not detected. This property can be used in the assignment of spectra of large fluorinated molecules. Another conclusion which can be drawn from the data is that 2JcF shows a definite dependence from the degree of substitution of the involved carbon, being larger for a secondary than for a primary carbon, while the opposite trend is observed for 2JcH: ’ JCH~-CF, _ _
J gH;-CE”r= J,,-C,, JcFrCF, = J,F,-Cg, Finally comparison (Table 2) of J,,
with J,,
< J,FS-CISS
in the same fragment for lJ, 2J, sJ shows that is
Table 2. Comparison of JHF with J,, No. of bonds
JHF
JCF
JHFiJCF (average)
1 2 3
615* 45.5~67.2* 13*2-10.2$
274238t 29.P26.6t 7.2-3.5t
2.4 1.8 2.2
* Ref. 2. t This work. $ Ref. 3. valid the empiricalrule J,, - 2 J,,. of its possible stereospecificity.
The coupling sJ,,
merits further study in consideration A. DE Maauo G. GATTI
Istituto di Chimica de& Mamnnoltxole V,ia A&n.so Cod 12 Milano, Italy [S] B. I. IONIN and B. A. ERSHOV,Plenum Press, N.Y. (1970). [3] A. DE &LSCO and G. GATTI,O.M.R. 8, 599 (1971).