Tetrahvdron Letters ~~.56, pp. 4895-4896, 1970. Pergamon Press. Printed in Great Britain,

RING INVERSION IN TRIMETHYLENE SULFATES

Gordon wood, John M. McIntosh, and Maurice MIskow

Chemistry Department, Unlveralty of Windsor.

Windsor. Ontario. Canada.

(Received in USA 6 October 1970; received in UK for publication 2 November 1970)

A recent publication1 cites an ultrasonic relaxation experiment on

4-methgltrlmethylene aulfate (la) which Is Interpreted In terms of a chair/

chair ring Inversion with a barrier of A += 6.2 kcal/mole (more stable+

less stable).' Conslderatlon of thls molecule seemed to offer no explanation

for the marked difference between this value and that of 10.3 kcal/mole for

cyclohexane. 3 In order to verify the publlshed result, we prepared the

related 5.5-dlmethyltrlmethylene sulfate (l&j and recorded Its low-tempera-

ture n.m.r. spectrum. The barrier to chair/chair Inversion of ia is 8.1

f 0.2 kcal/mole based on the coalescence of the AB methylene quartet (Tcr -107'C:

JAB= 10.5 * 0.1 &.:A+ ABE 24.5 Hz.) or 8.4 f 0.2 kcal/mole tased on the

coalescence of the methyl singlets (Tc- -109~~:&= 22.0 2 0.1 Hz.). 4 For

trlmethylene sulfate itself, preliminary experiments have Indicated that

the bsrrler Is of a slmllar magnitude, lndlcatlng that the sterlc Interactlone

In 2 do not affect the barrier significantly.

For s chaIr/chaIr Interconversion, the barrier In 4-methyltrlmethylene

sulfate (la) would be expected to be at least as great as that for 3.

Since It 1s known that the ultrasonic relaxation technique cannot, by Itself,

lead to any 1dentlflcatIon of the species Involved In a conformatlonai

equilibrium5 It seems likely that the value of 6.2 kcal/mole Is a measure

of the conformational barrier between a chair and an energetically low-lying

non-chair form. A similar situation has appeared In a substituted 1,3-dloxane

4895

4096 No.56

where aooustloal mearurement8 6 give A I@= 5.0 koal/mole, whereas n.n.r.

experiments give a value of 8.4 koal/mole. ?' Thlr apparent conflict has

been resolved,by asrlgnlng the lower barrier to a ohalr/non-ohair ohange.6

The implications of these results Tor the oontormatlonal analysi8 of

trlaethglene sulfites will be the subject of a future publication.

0

9 ,Lo

O/

P R2

%

Aaknowlednementsr

&ii RI’ CH 3 R2=H

Ilr RI' H R t CB 2 3

We ttiank The National Research Council of Canada for financial support

and Hr. D. HI11 for technical assistance. The many helpful dlscusslons

with Dr. G. Buchanan are also greatfully aoknowledged.

References:

1. R.A. Pethriok, E. Wyn-Jones, P.C. Ramblin and R.F.W. Whlte, J. Chea. Soo.

(A), 2552 (1969).

2. Entropy effeots are too small to affect the argument to be presented.

3. G. Bin8ch In @Topic8 In Stereochemi8trYn, Vol. 3, E.L. Ellel and N.L.

AllInger, ed., Interscience, New York, N.Y., 1968. p. 158.

4. Heaaured in 211 CD2C12:C2D5Br at 60 MHZ. Uncertainty In the temperature

measuremente are f 2'C.

5. R.A. Pethrlok and E. Wyn-Jones. Quart.. ReV8.. a, 304 (1969).

6. G. Ecoleston and E. Wyn-Jones. Chem. Commun., 1511 (1.969).

7. J.E. Ander8on. Chem. Commun. 669 (1969).