Ikck I 11;1.11 I I.: - 2 spectri ) p h tc ) I i ic ter. 'The analysis revenled oiily d ) ( J L l t 1..1a i i c l .3.0 xtoiiis of tlcuteriuiii per iiiole for stiiiplcs .I ;tilt1 I), respectively. The oxitkttions were carried out :Lt (is" using azotliisobutyroiiitrile as the catalyst aiitl chlorobenzene as the solvent. -1sensitive constant pressure apparatus was used to iiieasui-e the voluiiies of oxygen consumed. 'I'he results are sunimarizetl in Table I. TA11LIL ' h i s ICtsr,ATl\,k;
I
I ~ AiiI 01:OXII)ATI(JX IIP CUMENE APU'I) 1 ) l C G I'liKI JC'UMLXU
A d d e ~ iInliil,itnr
Curnl~r~iind
1 )etiteri~riiiriciic.I
kalfiu
0.91 1 )cuteriiciiiiici~c11 Sl)rlc 0.85 I ) c i i t c . r ~ ~ c u ~At ~ e t i ~ ~/ ~ - S i ~ r o ~ ~ l i ~ ~ ~ i o l 1 0 5 I ) ~ ~ ~ t c . r i ~ c u ~ 1i5i c i i c : /,-Sit r~~~ilieiirii I .07 I )cuterimiiiiciic A ~,1-l~icl1lor~i~ 11 ~ l i c i i ~1 . I!) I )euterocuiiiciic I$ ~ , 1 - l ~ i c i i ! 1 ~ r ~ ~ ~ l 1 e t i ~1 i l27 SlJllC
Froiii the (1iit;t iii Table I i t can readily be see11 that both of the effects cliscussctl above ;ire in operatioil. The two effects were separated by the addition of ;ti1 inhibitor to replace the usual tcr~iiinationstci).G Thc ratio of the inhibited rates represent the secondary isotope effect and indicate that hyperconjugation is important in stabilizing free radicals. The effect on the chain terniinating step is much larger since i t coiiipletely overshadows the secontlary effect, even though the over-all rate of oxidation is proportional to the inverse square root of the termination rate constant. Such an effect probalAy iiieans that the chain terminating step irivolves scission of a p-carbon-hydrogen bond and could be written thusly' 2CsH~C(CHa)200+ CsHS-C(CHJ2OOH
+ C$HjC(CIIJ=CH2 +
0 2
1 % iiic.:tsuriilg ~ t I ic
rigitl I
!ii
~i
~
iii
)diwhere t hc
projection, is vir-
S;LIII~ ;ts i l l ;t 1)I;tliai-c~-~~l~,~~eiit:tii~iie,~
o?)t:iiiietl for a-broiiiiiic :t slliiL o f 1 1 c i ~ i . -aiitl ~ a-clil~)rinc~ a siiift of I S - I ! ) e1ii.--'. These are interiiiediate',''c or borderline \r;tlucs',l,l' between those reportc!! for axial aiid equatorial halogens in six iiieiiiLere(1rings. Tlic good agreeiiient (T:tl>lc I) hetwccii tlic shifts for a-c!ilt,rvc:tiiil,li(!r (11, 1i3 = H , I< = C1) and a'-clilcii-oc:!iiiphor (11, I
