COXMCNICATIONS TO THE EDITOR
4194
adeiiosiiie \\-ere condensed according t o the general procedure. T h e tleacylation was carried o u t in 15 -11methanolic ammonia for 20 h r . antl the desired product \vas obtained in 65C; yield using an extinction of 27,100 a t 252 ni@( p H 6 ) . Guanylyl-i3’-t5’~-cytidine.--Pyridinium S2,O2’,0j’-triacetyIwere guanosine 8’-phosphate and S,O2’,O3’-tribenzo~-lc~tidine treated under the stanrldrd conditions. After giving t h e methanolic ammonia treatment for 20 h r . the dinucleoside phosphate was obtained i n 26“; yield using an extinction of 1A,900 a t 271 m p ( p H 6). Guanylyl-(3’~5’~-guanosine.--Pyridiniuni S 2 , 0 “ , 0 5 ’ - t r i acetylguanosine 3’-phosphate and S2,02’,03’-triacetylguanosine were condensed by t h e dicvclohex!.lcarbodiirriide procedure. T h e deacetylation \vas carried o u t in aqueous 7.5 S ammonium hydroxide (25 m l . ) for 50 hr. a t room temperature. T h e yield was 31 ,c; assuming no hypochromicity for the product. Guanylyl-(3’--.5’)-uridine.--Pyridinium P , 0 2 ’ , 0 5 ’ - t r i a c e t y l were conguanosine 3’-phosphate a n d O2’,O3’-dibenzoyIuridine densed under t h e standard conditions. T h e deacylation was performed with a mixture of aqueous concentrated ammonium hydroxide-pyridine (1: 1; 25 m l . ) for 35 hr. T h e desired product
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was obtained in X C { ,yield using a n extinction o f 20,800 a t 282 r n p ( p H 7 ) . Degradation by t h e Lactobacillus uc-idoph7i~sI-1y1-(3’+Sf)-cytidine (0.5 pinole), cytidylyl-(:3’+.i’)-uridine (0.6 @mole),cytidS-IJ.l-(3’~5’!-adenosine ( 0 . 3 pmole), antl c~tidy-lyl-(3’-t5’!-guanosine(0.6 pmole i were each incubated with t h e purified venom phosphodiesterase preparation?g using amounts previously standardized.24 Degradation to the ekpected nucleosides a n d nucleoside 5’-phosphates \vas complete as followed by paper chromatography in the solvent 2-propanol-0.1 .I4 boric acid-concentrated atnmonia 7 : 2 : 1, of the nucleoside 5’-phosphates \vas further confirmed by elution of their spots and subsequent paper electrophoresis a t pH
7.1. ~~
(29) W. E. Razzell and H. G . K h u r a n a , J . Bioi. C h e m . , 236, 210.5 (19.j9).
COMMUNICATIONS T O T H E EDITOR Bridgehead Adamantane Carbonium Ion
Sir: Previous investigations have established the unusual bridgehead positions of bridged ring systems toward carbonium ion processes. 2-6 The considerable variation--l0l3-in solvolysis rates between bridgehead derivatives in different ring has been a t tributed t o changes in conformational strain factors in proceeding from the ground state to the transition state.*“z5 Estimates of angle strain provide a satisfactory quantitative explanation for the l o 3 reactivity difference between t-butyl bromide and 1-adamantyl bromide ( I ) , but do not account for the further lo3 difference between I and 1-bicyclo [2.2.2]octylbromide ( I I ) . j The geometry around the reaction sites of both I and I1 is the same, and both would be expected to have nearly the same solvolytic reactivity, on the basis of angle strain considerations.2-6 Br
sponding bridgehead carbonium ions IV and V The geometry of ions IV and V is ideal for C-C hyperconjugation,’ which, conceivably, might be of greater importance for IVa (all second degree contributing hyperconjugative forms) than for Va (all first degree contributing hyperconjugative forms) Such hyperconjugation might thus account for the greater reactivity of I over I1 Doering and co-workers4 found t h a t solvolysis of l-bromo-3,3-dimethylbicyclo [ 2 2 2loctane (111) was about two times more rapid than that of 11, C-C hyperconjugation (compare \.’a and Vb) might be responsible for the accelerative effect of methyl substituents. since in Vb one of the contributing forms is tertiary
R”QR
R‘
- R’wR R’
X possible explanation for the rate spread between I and 11 is based on electronic differences in the correi l ) P r e i e n t e d a t t h e 117th S a t i o n a l l l e e t i n g of t h e American C h e m i c a l ’hiladelphia. P a . . .Ai>i-iI. 10ti-l. Abbtracts, p 2 2 N . 1- hack#i-ound d e t a i l s , i e e l a ) I< C I:oj-t, J r , a n d P vtjn I < . Schleye ‘im , 64, 2 7 7 ( I ! M M ; 1 h 1 P. v u n I< S c h l e y e r , I< C Fo!t, J r . , \V 1
II!ltW
lievie!\?: I ) I< h p p l e q u i s t a n d J I ) R o b e r t s . (hc111 R e z ’ , 64, 10% ( 1 0 . 5 4 ~ . 1,’ S c h i i l l k r ~ p fA , i ~ a v s ( ‘ h r i n , 1 2 , 147 (1960). 14) \V \-on E I h e r i n g . 51. I.evitz. A S a y i g h . S I S p r e c h e r , a n d 1%’. P. X‘hclan. J r J . A m i‘hrrn Sor , I S , 1008 ;103:1) i c e 51 F i n k e l s t e i n . P h I ) T h e s i i . Yale YniLersity, 1935, and ref 10. 1.i) P von I< 5chleyer and I< I ) h-icholas, J . A w . C h ~ 1 n S o c , 83, 2700 I 1 $)ti1). , t i , H. S t e t t e r , J > l a y e r , > I Schrvarz. and K . \ViiIlT I L v , 93, 2 2 6 (1!360), I f . S t e t t e r a n d P . Goebel. i h i d . , 96, 550 (196,3).
I.a, I< = H b , I< = CHj
I t has been argued earlier that hyperconjugative differences of this type do not contribute significantly ( 7 ) 51 J N . Y , 19R2
S . Ileivar. “ H y p e r c i , n j u g a t i o n ,
’
I
