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Muonium addition to 9-octalin: Observation of the muonated 9-decalinyl radical.
-t92 ss.00 + .w ~~F%SL.td
Tedrdubm Lenas, Vol. 33. No. 38. pp. 5617-5620.1992 RimcdinGtiBriuin
Muonium Addition to 9-Octalin: Observation of the ‘Muonated 90Decalinyl Radical. IvanD. Reid, Pant S&me-r Institute,CH-5232Villigm PSI. Switxdand. Christopher J. Rhodes,* Dcpamcm
of ChuGstry. QueenMaryand WestfieldColkgc, Universityof L.endon.MileEnd Rosd,London.El 4NS. Emil Roduner,
Fl~ysikalischChemisehes Institutdcr Univmitat Zurich,Wiirthurersuasse 190,CH-8057Zurich,SW-.
Abstract Implantationofpositive muon.9into a neat sampleof 9-octalii at 298K kd to the formationof a sin& 9decalinyl radical,in ccmast with expectationfmm a prcviomclaim thatthe 9dccalinyl radicalexists in distinctcis and tr(uuforms.
Several years ago.* it was mpotted by Lloyd and Williams that hydrogen atom abstraction from 15sand from fruns decslin by photochemically genemted But-0 radicals led to distinct cis or rrwrs 9decalinyl radicals, as a consequence of non-planar radical centres with appreciable banks
to isomerisation by inversion. This
raised the possibility of an interesting extension of our work on muonated cycloallcyl radicals~~ in which we could determine the barrier to out-of-plane inversion of an allcyl radical dimcdy, which has not to our knowledge been achieved. We expected, as in previous measurements of ison&c radicals,6~7that under high transverse magnetic field conditions four lines would be obsetved. corresponding to the +J/2, - l/2 ms states of the unpaimd electron in each of the two radicals as detected by flR Jn fact, the spectrum shown in figure la was recorded, which shows the presence of only a single radical, as is confirmed by the correlation spectrums (figure lb). This shows that the radical centm is actually planar, otherwise both ison~rs would be detected. While this work was in progmss, results were obtained by Robert&’ using using e.s.r. spectroscopy which show that the same bridgehead radical is formed from either cis or rrafis 9chlorodecalm. in accord with the view of a planar 9-decalinyl radical (I). The radicals observed by Lloyd and Williamst appatently do not arise via bridgehead hydrogen atom abstraction from decalin, but have other causesP
5617
5618
It is in any case interesting to compare the muon-electron coupling in the muonated 9decalinyl radical (390 MHZ, leading to a proton equivalent, or “reduced” muon coupling of 43.86) with that measured by Roberts9 (38.70) for the bridgehead proton in the protic analogue. On this basis, we obtain a hypertine isotope ratio of 1.13 which is at the lower limit of the range normally observed for confosmatlcmally constmlned alkyl radicals,5 and rather as was found to the be case for muonated cyclohexyl radicals3, suggests that the muonated 9-decalinyl radical is unable to weight conformations in which the muon is mom strongly coupled, in contrast with results for open-chain alkyl radicals~ and for the cycloheptyl radical3 where the ratios are all close to 1.4. Thus it is the case for 9-decali.nyl and cyclohexyl radicals that the overall dynamic requirements of the ring systems provide a quite rigid control that overrides any possible stabilising mechanismto*tl arising from the diering
dynamic behaviour of the bound muon (muonium atom) which, on the time average, would increase its
coupling over a corresponding proton.5
Acknowledgement
We thank the Paul Scherrer Institute, the Swiss National Science Foundation and the Leverhulme Trust for fmancial support of this work, and we am grateful to Dr. B.P. Roberts for communicating his results to us prior to publication.
References
Lloyd, R.V. and Williams, R.V., J. Phys. Chem., 1985.89, 5379. Rhodes, C.J.; Symons, M.C.R.; Cox. S.F.J.; Scott, C.A. and Roduner E.. Hype&e 1986, 32. 769. Rhodes, C.J. and Roduner, E., J. Chem. Res. (s), 1991, 196.
Interactions,
5619
4.
Roduner, E. and Reid, I.D., Israel J. Chem.. 1989.29.3.
5.
Rhodes, C.J. and Symons, M.C.R., J. Chem. Sot.. Faraday Trans. I, 1988. S4.1187.
6.
Rhodes, C.J. and Roduner. E., J. Chem. Sot., Chem. CO~WWI., 1988, 1227.
7.
Strub, W., Roduner, E. and Fischer, H., J. Phys. Gem..
8.
Reid, I.D. and Roduner, E., Structural Chem.. in press.
9.
Roberts, B.P., Tetrahedron Len., 1991.5385.
10.
The sample of 9octalin
1987.91, 4379.
was obtained from Aldrich and was degassed via four freexe-pump-thaw
cycles prior to being sealed into a 35 mm diameter thin-walled glass ampoule. llte sample was exposed to a beam of spin-polarised positive muons at thepE4 channel of the Paul Schermr Institute, Villigen, Switzerland An external magnetic field of 0.2T was applied to the sample in a tra&erse direction to the muon beam. Full details of thepSR technique have been given previously, %long with the data processing pmcednres; for the present study data mtalling 4 x 107 good decay events were accumulated. 11.
Roduner, E. and Fischer, H., Chem. Phys., 1981.54.261.
I
-.
.
*
1
200
150
(a)
.
.
.
.,
250 FREQUENCY
Transverse-field
rocncrled in ltqntd
,
,
,
I
300
350
(MHZ 1
pSR spectruml’ +octaltn
,
from the radical
nt 29RK.
(I)
’
*
.
I
300
350
(b) of
Correlation e airqte
400
spectrum radical.
(Received in UK 7 July 19%)
450
of
the
$00
ahove,
ConftrminR
550
the
’
’
.
,
400
Presence
’
Tedrdubm Lenas, Vol. 33. No. 38. pp. 5617-5620.1992 RimcdinGtiBriuin
Muonium Addition to 9-Octalin: Observation of the ‘Muonated 90Decalinyl Radical. IvanD. Reid, Pant S&me-r Institute,CH-5232Villigm PSI. Switxdand. Christopher J. Rhodes,* Dcpamcm
of ChuGstry. QueenMaryand WestfieldColkgc, Universityof L.endon.MileEnd Rosd,London.El 4NS. Emil Roduner,
Fl~ysikalischChemisehes Institutdcr Univmitat Zurich,Wiirthurersuasse 190,CH-8057Zurich,SW-.
Abstract Implantationofpositive muon.9into a neat sampleof 9-octalii at 298K kd to the formationof a sin& 9decalinyl radical,in ccmast with expectationfmm a prcviomclaim thatthe 9dccalinyl radicalexists in distinctcis and tr(uuforms.
Several years ago.* it was mpotted by Lloyd and Williams that hydrogen atom abstraction from 15sand from fruns decslin by photochemically genemted But-0 radicals led to distinct cis or rrwrs 9decalinyl radicals, as a consequence of non-planar radical centres with appreciable banks
to isomerisation by inversion. This
raised the possibility of an interesting extension of our work on muonated cycloallcyl radicals~~ in which we could determine the barrier to out-of-plane inversion of an allcyl radical dimcdy, which has not to our knowledge been achieved. We expected, as in previous measurements of ison&c radicals,6~7that under high transverse magnetic field conditions four lines would be obsetved. corresponding to the +J/2, - l/2 ms states of the unpaimd electron in each of the two radicals as detected by flR Jn fact, the spectrum shown in figure la was recorded, which shows the presence of only a single radical, as is confirmed by the correlation spectrums (figure lb). This shows that the radical centm is actually planar, otherwise both ison~rs would be detected. While this work was in progmss, results were obtained by Robert&’ using using e.s.r. spectroscopy which show that the same bridgehead radical is formed from either cis or rrafis 9chlorodecalm. in accord with the view of a planar 9-decalinyl radical (I). The radicals observed by Lloyd and Williamst appatently do not arise via bridgehead hydrogen atom abstraction from decalin, but have other causesP
5617
5618
It is in any case interesting to compare the muon-electron coupling in the muonated 9decalinyl radical (390 MHZ, leading to a proton equivalent, or “reduced” muon coupling of 43.86) with that measured by Roberts9 (38.70) for the bridgehead proton in the protic analogue. On this basis, we obtain a hypertine isotope ratio of 1.13 which is at the lower limit of the range normally observed for confosmatlcmally constmlned alkyl radicals,5 and rather as was found to the be case for muonated cyclohexyl radicals3, suggests that the muonated 9-decalinyl radical is unable to weight conformations in which the muon is mom strongly coupled, in contrast with results for open-chain alkyl radicals~ and for the cycloheptyl radical3 where the ratios are all close to 1.4. Thus it is the case for 9-decali.nyl and cyclohexyl radicals that the overall dynamic requirements of the ring systems provide a quite rigid control that overrides any possible stabilising mechanismto*tl arising from the diering
dynamic behaviour of the bound muon (muonium atom) which, on the time average, would increase its
coupling over a corresponding proton.5
Acknowledgement
We thank the Paul Scherrer Institute, the Swiss National Science Foundation and the Leverhulme Trust for fmancial support of this work, and we am grateful to Dr. B.P. Roberts for communicating his results to us prior to publication.
References
Lloyd, R.V. and Williams, R.V., J. Phys. Chem., 1985.89, 5379. Rhodes, C.J.; Symons, M.C.R.; Cox. S.F.J.; Scott, C.A. and Roduner E.. Hype&e 1986, 32. 769. Rhodes, C.J. and Roduner, E., J. Chem. Res. (s), 1991, 196.
Interactions,
5619
4.
Roduner, E. and Reid, I.D., Israel J. Chem.. 1989.29.3.
5.
Rhodes, C.J. and Symons, M.C.R., J. Chem. Sot.. Faraday Trans. I, 1988. S4.1187.
6.
Rhodes, C.J. and Roduner. E., J. Chem. Sot., Chem. CO~WWI., 1988, 1227.
7.
Strub, W., Roduner, E. and Fischer, H., J. Phys. Gem..
8.
Reid, I.D. and Roduner, E., Structural Chem.. in press.
9.
Roberts, B.P., Tetrahedron Len., 1991.5385.
10.
The sample of 9octalin
1987.91, 4379.
was obtained from Aldrich and was degassed via four freexe-pump-thaw
cycles prior to being sealed into a 35 mm diameter thin-walled glass ampoule. llte sample was exposed to a beam of spin-polarised positive muons at thepE4 channel of the Paul Schermr Institute, Villigen, Switzerland An external magnetic field of 0.2T was applied to the sample in a tra&erse direction to the muon beam. Full details of thepSR technique have been given previously, %long with the data processing pmcednres; for the present study data mtalling 4 x 107 good decay events were accumulated. 11.
Roduner, E. and Fischer, H., Chem. Phys., 1981.54.261.
I
-.
.
*
1
200
150
(a)
.
.
.
.,
250 FREQUENCY
Transverse-field
rocncrled in ltqntd
,
,
,
I
300
350
(MHZ 1
pSR spectruml’ +octaltn
,
from the radical
nt 29RK.
(I)
’
*
.
I
300
350
(b) of
Correlation e airqte
400
spectrum radical.
(Received in UK 7 July 19%)
450
of
the
$00
ahove,
ConftrminR
550
the
’
’
.
,
400
Presence
’