2298 (4) H. Hart and J. M. Sandri, J. Am. Chem. SOC.,81, 320 (1959): H. Hart and D. A. Law, ibid., 86, 1957 (1964): L. Birladeanu, T. Hanafusa, B. Johnson, and S. Winstein, ibid.. 88, 2316 (1966). (5) C. F. Wilcox, L. M. Loew. and R. Hoffmann. J. Am. Chem. SOC.,95, 8192 (1973). (6) P. R. Story and S. R. Fahrenholtz. J. Am. Chem. Soc., 86, 527 (1964); R. E. Leone, J. C. Barborak. and P. v. R. Schleyer in "Carbonium Ions", Vol. IV, G. A. Olah and P. v. R. Schleyer, Ed., Wiley-lnterscience, New York, N.Y., 1973, p 1860. (7) K. Fukui, Forischr. Chem. Forsch., 15, 1 (1970), and references cited therein. (8) C. F. Wilcox, Jr.. L. M. Loew, R. G. Jesaitis, S.Belin, and J. N. C. Hsu, J. Am. Chem. Soc.. 96,4061 (1974). (9) R. Hoffmann, Acc. Chem. Res., 4, 1 (1970); M. J. S. Dewar, "The Molecular Orbital Theory of Organic Chemistry", McGraw-Hill, New York, N.Y., 1969: E. Heillbronner and H. Bock, "Das HMO-Modell und seine Anwendung", Verlag Chemie, Weinheim/Bergstr.. Germany, 1968. (10 Calculational methods are described in ref 5. (11) Using perturbation expression 1, one finds:
stabilization
[ (0.72)(0.86) - 2(0.46)(0.32)]2 - 0.11
~
AEZ-3
This is to be compared wlth the stabilization of nortricyclyl which can be thought of as simply the interaction of methyl cation LUMO with cyclopropane HOMO -
[ (1 .00)(0.72)]2
0.52 AEI.2
4 . 2
Thus the stabilization energy due to the second cyclopropane in quadricyclyl should be no greater than 0.1 1/0.52 = 0.21 of the initial stabilization in nortricyclyl. This fraction is reduced still further since A€,-d < AE2-4 (Le., the methyl cation LUMO is lower than the cyclopropyl carbinyl LUMO). This 'simple perturbation theory result is to be compared with the experimental relative rates
I
I
log
(2.)
log
=
(1)
1.2
-
= 0.14
(12) This species is stabilized yet further, of course, because of relief of angle strain at the cationic center. It is the intention of this paper to focus on only electronic effects, however. (13) Using the procedure of ref 11, (.4--H)2 a 0.47 for the interaction of cyclopropane wkh the already strongly stabilized cyclopropyl allyl cation: this represents 90% of the stabilization due to interaction of cyclopropane wlth methyl cation. (14) M. J. Goldstein, J. Am. Chem. SOC., 89, 6357 (1967); M. J. Goldstein and R . Hoffmann, ibid., 93,6193 (1971).
Leslie M. Loew* Department of Chemistry State University of New York at Binghamton Binghamton, New York 13901 Charles F. Wilcox Department of Chemistry, Cornell University Ithaca, New York 14850 Received November 23, 1974
The Gaseous Tetramethylenechloronium Ion' Sir:
The formation of chloronium and bromonium ions in the gas phase was postulated* to explain the dominant peaks in the mass spectra of higher 1-haloalkanes (eq 1). Despite the apparent general acceptance of this rati~nalization,~ and the postulation of similar cyclization-displacement reactions involving anchimeric assistance to explain3 unusual
r.+ 1, R = C,H,; Y = Y' = H
R = C2H5; Y lb, R C,H,; Y la.
= H; = D;
Y' Y'
2
=D =H
Journal of the American Chemical Society
/
97.8
/
Table I.
Partial Mass Spectra of Labeled 1-Chlorohexanes Relative abundance
Compound
?n/e
lChlorohexane 1Chlorohexane-l,l-d, l-Chlorohexane-4.4-d,
90
91
92
93
94
95
0.3
72. 0.2 0.5
3.6 1.9 1.6
23. 70. 71.
1.3 3.8 3.8
23 22
Table 11. Collisional Activation Spectra of C,H,35C1+ and C,H,D,35C1+ Ions13
mle 27 28 29 30 31 39 40 41 42 43 47 48 49 50 51 52 53 54 (55) 61 (62) (63) 73 74 75 76 77 78 90 91 92
1Chloroheptanea 16 4 9.2
1-Chlorohexanea 15 4 0
1-Chlorohexane, 18 eVa 16 4 9.1
4 2 9.6
5 2. 9.5
14 2 8.3
1.1 0.5 2 1. 3.4 0.5 7.2
