Sept. 20, 1963
COMMUNICATIONS TO THE
inductive effect is obscured by concurrent conjugative effects. ( 7 ) National Science Foundation Predoctoral Fellow, 1960-1963; m a n K o d a k Science Award in Chemistry, 1962-1963
DEPARTMENT OF
CHEMISTRY
00
East-
R . G . LAWLER'
2835
100
rl. STREITWIESER, JR.
UXIVERSITY OF CALIFORNIA BERKELEY4, CALIFORNIA RECEIVED JULY 17, 1963
EDITOR
n
-
0
x
60-
40-
Tritiodeprotonation of Biphenylene Because of its unique structure, biphenylene has been of considerable chemical and theoretical interest for some years.* The molecular orbital prediction3 that the 2-position is the more reactive has been confirmed by repeated observations of exclusive reaction a t the 2-position b y several electrophilic substitutions : nitration, halogenation, acylation, mercuration, et^.^,* KO data have been available hitherto relating to the important question of the quantitative relative reactivities of the 1- and 2-positions. %-e now wish to report the rates of tritiodeprotonation for both the 1and 2-positions of biphenylene. The exchange medium, tritiated trifluoracetic acid70yo perchloric acid (96.9:3.1 b y volume), is similar to t h a t used by Eaborn and Taylor5 in their studies of detritiation of tritiated aromatic hydrocarbons. Biphenylene undergoes progressive decomposition to tars after long reaction times; hence, the biphenylene was isolated from each kinetic aliquot by sublimation and its purity was monitored by g s . analysis before counting on a h'uclear-Chicago Model i 2 4 liquid scintillation counter. The kinetic problem is t h a t of two parallel and reversible first-order reactions. The total specific activity a t equilibrium is the sum of the activity of the 1- and 2-positions; therefore, a plot of log ( D P M m D P X t ) Z~S.time gives a curved plot (Fig. 1) correspond20 0 -
X
X I 0 a
0
8
* 6 I a n -
z e4
Sir:
4
Time, min.
Fig. 1.-Kinetic run for tritiodeprotonation of biphenylene a t 25".
ing to the two different reactions. After the first reaction has reached equilibrium, the points representing the slower reaction (presumed to be cy) can be extrapolated back to zero time. The value of DPMt=o should be half t h a t of D P M m ,and this value, as well as corrected DPMt values, can be used to ascertain the rate of the faster reaction (presumed to be /3) as shown in Fig. 2. ( 1 ) This research was supported in p a r t b y a g r a n t from t h e United S t a t e s Air Force Office of Scientific Research of the Air Research a n d Development C o m m a n d ( 2 ) T h e chemistry of biphenylene has been reviewed recently by W . Baker and J. F W. McOmie in D . Ginsburg's "Nowhenrenoid Aromatic Compounds," Interscience Publishers, I n c . , New York, S. Y . , 1959. ( 3 ) R D. Brown, Trans F a r a d a j SOC.,46, 140 (19.50). 14) U'. Baker, M. P . V. Boarland, and J F. W. McOmie, J Chem Soc., 1476 119.54). U'. Baker. J W B a r t o n , and J. F W McOmie, ibid, 2638. 2666 (1959), W B a k e r , J F W. McOmie, D . R Preston, and V. Rogers. ibid, 4 1 4 (1960) ( 5 ) C E a h o r n and R T a y l o r , ibid , 1012 (1901):
-
n 0
20-
I 8
I a N
I O --
1
0-
Y
-
6-
0
100 5
200
3 0 0 400
I O 15 Time, min.
2 0
Fig. 2.-Analysis of kinetic run into simultaneous first-order reactions for the 1- and 2-positions of biphenylene. The bottom time scale is for the 2-position.
This method was applied to naphthalene and gave rate constants of 3.4 X lo-* and 5.6 X set.-'. The ratio of rates (6.1) is virtually identical with that obtained by Eaborn and Taylor5 ( k , = 5.3 X set.-'; kp = 8.85 X 10-j set.-') and similar to that (7.6) obtained by Dallinga, et u Z . , ~ for CF3COODD2S04-CC14. Biphenylene gave k , = 4.32 X I O F set.-' and k p = 2.75 X lop3set.-'; k p , ' k , = 63. This ratio, which has also been confirmed by detritiation of specifically labeled biphenylenes, agrees qualitatively with various molecular orbital predictions but is in serious quantitative disagreement. Localization energies, for example, predict k o , j k , e 4.7 This limitation in an important quantitative application of simple molecular orbital theory is, furthermore, not significantly improved by introduction of the a-technique. (6) G . Dallinga, A. A. V . S t u a r t , P J S m i t , a n d E I , Mackor. Z !
