The author would like to thank The Upjohn Company and the National Science Foundation for. These results lead to the hypothesis that the direct interaction between the metal and the electrophile is of great importance in the eletrophll1c subst1tut1on reactions of metallocenes. Treatments 01' the electronic structure or meta11estimate8 give a more precise location of the metal's electron density.
RESULTS 1 Competitive Ac.~lationa
The rate constant ratIo, R, is calculated from Equation 2 using the amount of aoethylferrocene and the total amount of acetylated d1ethylferrocene obtained to estimate the final concentrations of ferrocene. Any unusual polar effect in the metallocene system would be expected to increase the dissociation constants of ferroene-ocarboxylic acids.
C6HSCH2COOH
DISCUSSION
An attacking eleo~ph1le eventually binds to one of the carbon atoms of the carbocyclic ring. Conversely, steric interactions can be alleviated by bending the C-E bond away from the axial direction of the metal. Connection of the electrcph1le oceurs with both the metal-ring connecting orbltales and, aa explained by.
AICI - 4
As for binding to ring 18, thi8 means that the electrophile must bridge a greater extent in the heavier metallocenes. It is a bridge-like structure 18 that must be maintained (Fig. 4), either the structure will become distorted or the bond to the rings will be weakened, although bonding to the central metal may partially compensate for 10S8 of the bond energy. S1mple molecular orbital approximations made for substituent effects 1n metallocenes 1 indicate that the a-position should be more reactive than the ~-poait1on i.
W -Pemoewlalkano1e Ae1de
The steric effect of the phenyl E~OUP is to hinder the solvation of the roaction center. This steric effect dictates that the removal of the phenyl group from the reaction. terrain with increasing ohaJ.n len;;th will increase the sol. The alkyl chain len;:de 1s critienl as ring size must be proper to enable participation. 2-phenyl-1-ethyl~-toluenesulfonate-solvolyzes at about: if.1 at least one third of the rote of ethyl.,2-toluenesulfonate. sUt;i!.ests that the inductive and steric effect,s of the phenyl.
HCOOH
Pigure 13
- lound
I'he solution.ion t'ltH3 dried over ol1hydroB. t'1Q.:~neG1urll BUlf~ate, filtered and the filtrate evaporated to dryness under reduced pressure. of the solvent gave an orange liquid, n. 3 Anhydrous acetic acid was prepared by heating under reflux for four hours or overnight in quantities of glacial acetic acid (Baker 8 analytical rea.::~ent) mixed in a voltml or . active anhydride followed by: 'ractional distll1iif\.g the solvent thrur,h Q 90 em. lon~; column packed \'lith Glass H.,aschig rin~.:B. $Olvent '.'IS::; deQ):;f:::;enated by bubblitl{~ a stream of oxygen • .free dry 111 tro.~en throu:-:;h it for a hS.lf'. It '.";ns with the desire to decide between these two alternative theories that the present investigation' of halogen (.ltion of l.;.-S,-hutyl- cycle:lohexcne 'I!as undertaken. Such roagento mi .)lt be hydro;~:cn chlori(le or " In l;-~-butylcyolohex~ne i£ the ~-butyl group becomesi3 axial .. it if.) is opposed only by a quani-axial hydrof:an s1nzle, 2nd . energy;Y dlrferene~ bctHeen an axial And equatorial ~-butyl .. group 1n eyclohextrne 1s therefore !3'f1W.more than in eyclohexs.no. .. and hydro:;en should greatly favor Xlllen. The .!c.-butyl group is sufficiently removed from. the double bond so as not to affect the collection while Qt at the same time keeping the 'olefin in a :f'1x,&d eonformnt. A test of the hypothesis that the 4-!-butyl f~roup exerts no influence on addition would result from comparing Q o£ .. products or unsymmetrical addition. It seer.1S . that any effectH ~. r)Util ~:;group of additives to 4,-&-butylcyclohexene! I have been attributed steric hindrance or enhancement effects (67). The relative amounts of each isomer were determined from tho aret'H'-; peaks of two kinct6 of' «rhydro~ens and clc?ar ma{;r.(:tic rC'sonance spectrum. On the b[u;in of: thet:e assigrunent:3., irji' A rare absorption occurred which resulted in long-term retention of up to:10) III of a mixture containing 16:~ of this isomer. In order to tt'"~ 1nflutmce of the ~-butyl group on adi tlor •• acetic acid was added. Jill blocked the approach of tht"l electrophile on one side of the rin.~ "/hieh reGtricts approaeh to on the other side (f 'lg. This process would seem powerless as one of the 'E!'nterinf:': t:rrups will be eclipsed. 1'The minimization of charge separation can OVERCOt'l10e any energy exchange due to t.twisting of the '7r bond. PyrolYEiiD was considered complete one hour after ester addition to the top of the column was complete. The organic layer of the product was examined from the aqueous layer, dried over calcium acid. And vacuum distilled t.Lrouf,:.h t.Podhlo1niak column. At intervals of a few minutes, portions of the reaction mixture were removed and ohchromatographed on 8. At the end of the reaction, the presence of hydrogen chloride was noted, and increasing amounts of chloropentanes WE"l'e. But in the dichloride mixture obtained on removal of acetic acid 4% of the long retention time isomer was found. HGe The retention time of the product on a Carbowa."C column differed greatly from the retention times of both products from the chlorination of 4-~-butylcyclohexonef. 75% of the olefin and that this olefin waB eomerized to an extent of ::.!om ) 0;:; in the other positional isOMores.. the corn position of the ncetHters was then, in the order of ascending J·ctent.ion t.ine, . 32;~. One is struck by the fact that the dryness of the easy-to-digest product (carbon) decreases as the hull of the 2-buffered product increases. It looks like there's a new ster1.c ei'Tect. begins to dominate \.mieh it':) sol":iE~how connected to,h most of the substit7.uentc, around the carbonyl ~;rout. Although the "'all .wq isomer II is the slowest, the difference is only a factor of 5.5 in rate. This can be explained if the steric crowding of the methyl groups 01-' eom~rable. Another example of an etheric effect in 2-substituted cyclohexyl derivatives is solvolysis. The result that the lithium aluminum hydride reduction of glG-2,6-dimf'!tylcyclohexanone r:iv(ls, but ll}~ the most stable iSOMer 16 is very noticeable compared to other rC:3ults Sf; reported in Yl' can III of of this rpult eonl5titutes. They give an alcohol, namely IVa (page 1(3), unless isolation of the alkoxide occurred during the reduction. This possibility is unlikely because the isomerization of the isomers: IV in the sodium atom). catalyzed by ketone is very 510\>1 even at :2100. 400 mL pentane was added to the clean filtrate and the layers were separated. The pentane layer was washed with :;00 ml and 8.i:: dissolved in water and dried over barium oxide. The desiccant MiS is removed by filtration. and the pentane was distilled on a. sterull bath leaving li liquid residues behind. 1. Chranatography on a diisodecyl phthalnte column at 1400 indicated the presence of small amounts of the 1,3-dimethyl. The alcohol mixture had an estimated 9O~J' of an iOllUitr whose retention time was 10.6 t;1 minutes and about 10; used to be; of an iamer whose retention time was 13.4 minutes. Vacuum distillation of the liquid residue through a 12 tnm. long f·ractionat.1on column packed with 3x3 mm. steel wire mesh cylinders. of the alcohol mixture in 80 ml. dinitrobenzoyl chloride in a steam bath for half an hour. The yellow solid which precipitated 'lae collected by suction and when air dried yielded le.O g. Chromatoeraphy or this material dissolved in 100 ml of methylene chloride and 50 ml of alumina packed in pentane envelope 6.7 G. SO . acetate. must have resulted in a r.ram nucleophilic attack by 801- ven t on the auxiliary sac.e or origin of migration as occupied by the migrated hydrogen. This type o:f mechani8r.1 can also explain the formation of tran!-3-~but11oyoloheX1l acetate from 4-!-butyl-. In the Stevens rearrangement, the origin of the migration is either nitrogen (ammonium halide) or crultur (sulfonum halide), and in the \<11 tt1g rearrangement the origin is an oxygen atom (l - 4). Both rearrangements are initiated by the base (for the Stevens rearrangement.,) hydrox1da, ethox1de and cm1de, and by the rearrangement Wl tt1g )phenyl and butylll thlwn, potassium amide, end ProWl80diu.~). '!' rearrangements can be formulated 88 follows' fig 1). The Stevens rearrangement has been shown to be intramolecular by applying the reaction simultaneously to two different compounds (which individually react at similar rates) in arunc r,ledlum and showing that there is no inter-. If the benzyl group were taught as an eet1on, the reverse order would be expected since the relative rates of bar deficiency of the corresponding benzyl halogens (1n-volVine of the ccrbon1um 1ntermGdiate ion, SN1) arc 1n. Moreover, if the migration involved a true carbonium ion (ie, not an internal ion pair) intermediot racemization would be expected for optically active r:11grat1ng groups while retention is observed (3). The data are also consistent with the rn1grst1on of group R a.s a carban10n (lb ,e) which rnovGs from the origin to terms. Contemporary displacement and failure to develop a significant positive charge on the migrating part of R should allow this reaction and a bridge. A possible exception to this statement is the reaction of 4-carnphyL~rcuric iodide With tr110dlde ion to give 4-.TAaLS I
Pisure 12
TADLE I
Substituted Cyclohoxllnones
GURE 3
