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6-1971 Photochemical Reactions of Some Benzyl Compounds Thomas Wesley Lesniak Union College - Schenectady, NY
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This Open Access is brought to you for free and open access by the Student Work at Union | Digital Works. It has been accepted for inclusion in Honors Theses by an authorized administrator of Union | Digital Works. For more information, please contact [email protected]. PHOTOCHEMICAL REACTIONS OF SO¥.E BENZYL CO!.POUNDS
by
Thomas Wesley Lesniak a c 197/ "'
Senior Thesi~ Subrratted in Partial Fulfillment
Of the Reouire1I1ir:mts of Graduation
DEPARTMENT OF CH.Elli.ISTRY UNION COLLIDE
,June 2, 1971 l il;11 ~2 L (_1,37. 1111 r~ «.z
This Thesis
Submitted by
to the
Department of Chemistry of Union College in partial fulfillment of the requirements of the degree of
Bachelor of Science with a ~ajor in Chemistry
is approved by
ii Abstract
1 Zimmerman and Sandel have investigated many photolytie. reactions - . involving benzyl compounds and have hypothesized the intermediate to be a carbonium ion. The addition of a ~-electron donating group
has been used to increase the stability of the carbonium. ion intermediate.
3, 5-Disubstituted benzyl carbo.nium ions have added stability.. If the carbonium ion is produced, one could expect to alkylate aromatic rings with it to produce a Friedel-Crafts producto With this in mind 3-methoxybenzyl bromide, 3-methoxybenzyl acetate, and 3,5-dimethoxy• benzyl acetate were photolyzed in dry benzene using radiation of JOO run.
The products were analyzed on a gas ehromatogra.ph and only a trace of Friedel-Crafts product was observed for the 3-methox.ybenzyl compounds.
The product from the photolysis of J,5-dimetho.x:ybenzyl acetate was found to be prtmarily the dimer of a free radical reaction. However, some Friedel-Crafts product was also obtained.
iii Table of Contents
Abstract •••••••••••e•••••••••••••••••••••••••••••••••••••••e•••it iii
List of Figures •••e••110•••••••••••••-.e•e•eeee••fl••••••••••••••••• v
Introduction •••-t••..,•••••~•&ee•••&o••••••&•ll!'•••••••••e•11t••••••••• 1
Discussion ••••8•e•e•••••••••ae••••••••••••••••••••••••••c&~•••••• 4
Conclusion ••ei111e•••••••••••••••••••••••••eeaee•••••••••••••••.,••• g
Experimental ••••••~•••O••••••••e••••••••••••••••••o••••it••••••e• 10
References ••~•••••••••••$•••&•••••••&••••••••••••••••6•••e•••••e 22
iv List 0£ Figures
Electron density calculations for electron donating groups and withdrawing groups on benzene in the ground state and first excited state •••••••.•.•••••••••••••••••••1 Reactions of 3-methoxybenzyl compounds beli.eved to proceed through the same carbonium ion intermediate ••••••••••••••2 Scheme of reactions studied in this research •••••••••••••••••••••3
Gas chromatog:rarn of the product obtained from the photolysis of 3-methoxybenzyl bromide in
benzene e ••••••••••••••••••••••••••• Ct •••• 14 NMR spectrum of the blank of the photolysis reaction of 3,5-dimethoxybenzyl acetate in
benzene It "" ••••••••••••• e •••• e •• e •• 15 NMR spectrum of the photolysis product from the reaction of 3,5-dimethoxybenzyl acetate in benzene ••••••••••••••••••••••"'••••••"'••••ee•••••t!••••-1'••"'9•e•••l6 NMR spectrum of the blank of the photolysis reaction of 3,5-dimethoxybenzyl acetate after removal of solvent .••••••••• 17 ~1MR spectrum of the nhotolysis product of 3,5-dimethoxybenzyl acetate stripped of solvent ••••..•••••••••.••18 Gas chromatogram of the blank from the photolysis reaction of 3,5-dimethoxybenzyl acetate in benzene ••••.••••••••••19
Gas chromatogram of the photolysis product from the reaction o.f J,5-dimethox:ybenzyl acetate in benzene •••.•.••.•••.••20
Gas chromatogram of the photolysis product from the reaction of 3,5-dimethoxybenzyl acetate after removal of solvent . " ..•...... ,,. e •••••• e ••• 21 ...... 41 • " fli •••••••
v Introduction
Many photolytic solvolysis reactions of benzyl compounds have been
studied and the reaction is thou~ht to proceed throu~h a carbonium ion
inte. rmediate. 1 ' 2 ' 3 By means of electron density calculations (Figure 1),
it can be seen that the electron densities for the JTleta-positions
increase appreciably from the ground state to the first excited state.
Thus, ~ta-electron donating substituents should increase the stability
of the carbonium ion intermediate.
D 1000 D U71 (-0.571) w 0.428 ( +0.572) 1.000 (0.000) 1.om ro.oooi 1.143 (-0.143) O.S57 ( +0.143) J .000 (OJ)OO) 1.000 (0 000) 6 6 1.143 (-0.143) 0.!157 ( +O 143) ·Ground states Fig. J .-Monosuhstitutcd benzene cicctron densities (W "' Cll2', 1> = Clh-:). Unparcnthcsizcd numbers are !!'-electron densities; parenthesized numbers are formal charges. /CH3 /CH~ 0 1.762 ( + 238) 0 I. %.1( +.OH) 0.nn(+.ozRJ · ·60.734( +.266) 1.167(-.167) J .028 ( - .028) 1.204(-.204) o.soo < + .001 l 6 0.762 ( + .2:311) 1.02! (- .021) fir1t Excited State Ground Stale Evidence for the carbonium ion intermediate can be seen in reactions of the type shown in Figure 2 where 3-rnethoxybenzyl chloride and 3-methoxybenzyl acetate ~ive rise to the same product under identical reaction conditions. This suggests that both reactions proceed throu~h the same intermediate. one can not conclude from reactions of this type that the carbonium ion is produced. It is possible that the reaction 1 might proceed via an ~r2 mechanism. These reactions also yield some free radical products. However, these are of little sii:&iificance compared to the priniAry reaction. + Dioxane- HtJ->- +free rA,tllcal :proauc~s Dioxa.ne-H20 +free ram.cal :proauc~s FiP-nre 2. Reactions of 3-~ethoxyhenzvl comoounds bel:i.eved to nroce ed throul'.'h the sar-e ca rborrium ion intermediate. Stability of the carb0nium ion is increased with the addition of a single meta-electron donatin~ substituent and can be further increased by the addition of another methoxy substituent to fonn the 3,5-dimethoxy• benzyl compounds. Besides improving stability, the disubstituted compounds also do not undergo free radical reactions which is an advant.aze in the identification of the photolysis products.1 If the inter~ediate in reactions of this type is assumed to be a carbonium ion, then one ~ight use the carbonium ion in the alkylat1ons 2 of aromatic rings. In this study 3-methoxybenzyl compounds and a 3,5-dimethoxybenzyl compound were prepared and photolyzed in the presence of benzene in the hopes of obtaining the correspondin~ Friedel-Crafts Producte. The 3,5-diir.ethoxybenzyl compound was also photoly7.ed in anisole. Fiirure 3 is the scheme of react:i.ons for this research. Figure 3. Scheme of reactions studied. Al Cl rnJCH2@ benzene~ ~ OCH3 hv benzene acetic ~o /CH20Ac hv > tlyd1±de> y benzene OCH3 hv OCH / OCH3YnlcH20Ac 3lo/8@ benzen~ ~ · OCH OCH3 or OCH0CH~CH2rnl°CH 3 3 - 0 ~ ~ 3 OCH3 OCH3 Discussion 3-Methoxybenzyl bromide was prepared and photolyzed in benzene in a 1:15 mole ratio of reactant to solvent. A small amount of hexadecane was added to the solution as a standard. The progress of the reaction was checked every few hours by injecting a small sample into a gas chromatograph. The ratio of new peak heights to the hei~ht of the hexadecane standard was used to see if a reaction was occuring and also as a relative measure of the rate at which it was proceeding. After' 20 hours the reaction was complete. As was expected, the gas chromatogram contained more than one major product peak (A.s stated in the !ntroduction, free radical products as well as those from a carbonium ion inter• mediate were anticipated). However, when most of the solvent was stripped off, the chromatogram showed seven distinct peaks (Fi.~re 4). The blank was then stripped of solvent and a small sample was injected into the chromatographe Again the chromatogram showed numerous peaks. All of the peaks in the chromatogram of the blank can not be a result of the absorption of light since the samples were covered with aluminum foil. The products corresponding to these peaks must have resulted from a thermal reaction. The largest peak in the chromatogram of the photolysis Product was found also in the chromatogram of the blank and mass spec.;.. trometry revealed that it was starting material. The rna,jor photolysis Product was collected for infrared analysis. The substance was not homogeneous; part of it was a clear, colorless liquid soluble in chloro• form, and the other was a red oil which was insoluble in chloroform. No data could be obtained from the infrared spectrum. A mass spectrum was obtained for the collected substance and it revealed that the material 4 had decomposed. It is interesting to note that a small peak was observed in the gas chromatogram of the photolysis product with the same retention time as the prepared 3-benzylanisole, the expected Friedel-Crafts product. (This peak is peak "F" in Figure 4). Of greater,·retention time was' another smaller peak (Peak "G" in Figure 4) which might correspond to a dimer product of the intermediate benzyl free radical. A 1:4 mole ratio of 3-methox:ybenzyl acetate and benzene was Photolyzed in an nmr tube for 72.5 hours. No visible change could be seen between the nmr spectrum after 72.5 hours of irradiation and the nmr spectrum before photolysis. Thus, little or no reaction occurred. Numerous problems were encountered in the preparation of 3,5-dimethoxy• benzyl alcohol. Zimmerman and Sandel1 report that the product can be obtained from a reduction of 3,5-dimetho:x:ybenzoic acid using equimolar quantities of the acid and lithium aluminum hydride in ether. However, this reaction was attempted several times with slight modlfications an.d none of the alcohol was obtained. Reduction of the correspondin.g methyl ester yielded only starting material using either tetrhydrofuran or ether as solvent~. Finally, the alcohol was obtained by the reduction of the corresponding acid chloride with lithium aluminum hydride. 'T'he reaction of acetic anhydride and 3,5-dimethoxybenzyl alcohol yielded 3,5-dimethoxybenzyl acetate, the desired material for the photolysis reactions. A 1:20 mole ratio of 3,5-dimethoxybenzyl acetate and benzene was Photolyzed in an nmr tube for 170 hours. An nmr of a blank (Figure 5) was compared to the nmr spectrum of the mixture after irradiation for 170 hours (Figure'6). It became obvious that better observations could be made if the solvent were stripped of. This was done and an nmr spectrum was obtained for the blank and photolysis products in deuterated chloroform. These spectra are Figures 7 and S, respectively~ In comparing the two nmr epectra, several features are apparent. First, the multiplet that appears in the spectrum of the blank between 6.53-6.84 ppm exists as a s·ing l et at 6.51 ppm in the spectrum of the photolysis product. second, the singlet at 5.29 ppm in the spectrum of the blank is completely missing from the photolysis product spectrum. Third, the singlet in the spectrum of the blank at 3.90 ppm appears as somewhat of a multiplet in the spectrum of the photolysis product. Fourth, the singlet at 2•18 ppm in the spectrum of the blank is not present in the spectrum of the photolysis product. Instead, numerous peaks appear from 1.,00-J.OO ppm including a triplet between 1.01-1.42 ppm. (All o.f the nmr spectra obtained are with an external T¥iS). The above discussion leads to the conclusion that the product after photolysis is a different substance th~n starting material. If the product obtained from photolysis were indeed the expected Friedel-Crafts product, then one would expect to see a different spectrum between 6.50-7.50 PJlll• The spectrum of the Photolysis product is in good a.llreement with what one might expect for the dimer of the free radical intermediate. From the nrnr spectrum of the Photolysis product, it appears that no starting material remains and that the reaction has gone to completion. This is seen in the complete disappearence of the peak which appears at 5.29 pµn in the spectrum of . the blank. A gas chromatogram of both the blank and photolysis product was obtained and is shown in Figures 9 and 10, respectively. In the chromato~ram 6 of the blank no peak appears beyond a retention time of 6 minutes. In the chromatogram of the photolysis product, a small peak appears after 8 minutes and a very broad and rather high peak appears with a retention t•l.Jne between 10 and 14 minutes. This means that the product formed' in the photolysis reaction is probably of a higher molecular weight than the startin.P; material. 'rhe peak with a retention tiI:le of B minutes probably corresponds to the Friedel-Crafts product. This can be better seen in Figure 11 which is the gas chromatogram of the photolysis product after removal of solvent. ~he large peak with a retention time of 10-14 minutes corresponds most likely to the dimer product of the intermediate benzyl free radical. A 1 :4 mole ratio of .3, 5-dimethoxybenzyl acetate to anisole was photolyzed for 70 hours. ~he nmr spectra of the blank and photolysis product were obtained and found to be nearly identical. However, some ferences were noticed in the section corresponding to the aromatic d'f1 hydro~ens. sev~ral small peaks are visible between o.60-0.90 ppm in the spectrum of the photolysis product which are a.bsent in the spectrum of the blank. A gas chromatogram was obtained for both the blank and the photolysis product. In the blank no peak was observed e...fter 7 minutes. However, a single peak was seen in the chromatogram of the photolysis product with a retention time of 11-12 minutes. This means that a reaction did occur and that a product exists which has a higher molecular weight than the starting material. 7 Conclusion 3-Methoxybenzyl bromide was flrst considered as a reactant in a photochemical reaction because bromide is a. good leaving group; thus, the carbonium ion intermediate could easily be formed. However, the use of bromide as a reactant has two disadvantages: bromides form radicals very easily upon photolysis and bromides also tend to decompose quite readily on gas chromatographic analysis. Since acetates do not decompose very easily, acetate was used as a leaving group instead of bromide in subsequent photochemical solvolysis~ The reaction of 3-methoxybenzyl acetate in benzene did not yield the expected Friedel-Crafts product. One should not conclude from this reaction that a carbonium ion intermediate was not formed. It is possible that the intermediate was formed and did not react with the benzene. 3-Methoxybenzyl acetate should be photolyzed in several different solvents. In this way one might better know whether a carbonium ion intermediate was fonned~ It must be restated that the identification of the photolysis Product to be the expected Friedel-Crafts product is not sufficient evidence to confirm that a carboniurn ion is indeed formed. The problems encountered in the preparation of 3,5-dimethoxybenzy1 alcohol can be explained in terms of insolubilities. Adams4 has reported that the reduction of free carboxylic acid is generally less satisfactory than the reduction of the corresponding esters or acid chlorides. The frequent problem is that an insoluble derivative is formed which is slowly reduced or not reduced at all. This was definitely evidenced in the preparation of J,5-dimethoxybenzyl alcohol frorn 3,5-dimethoxybenzoic acid. s The photolysis of 3,5-dimethoxybenzyl acetate in both benzene and anisole yie· ld ed the unexpected free benzyl radical dimer. Some of the Friedel-C ra ft s product was also probably produced. Thus, the hypothesis that a carbonium ion might be used to alkylate a benzene ring was shown to be possible even though the primary product .is probably the dimer of the benzyl free radi.cal intermediate. Perhaps part of the problem .for the low yield of Friedel-Crafts product is due to solvent. Benzene is not a good solvating solvent. The reaction should be run again in a polar, solvating solvent; dimethylformarnide should be i~vestigated. It is interesting to note that a reaction occurred with 3,5-dimethoxybenzyl acetate in benzene but did not occur with 3-methoxy• benzyl acetate in benzene. This data would seem to support the findings of Zimmerman and Sandell which state that a second meta.-methoxy group aids the photochemical reaction. Several procedures have to be completed yet to f:i.nish up this study. First, the products from the photolysis of 3,5-dimethoxybenzyl acetate in benzene and anisole should be more carefully analyzed. Then for final confirmation, the Friedel-Crafts product and dimer of the free radical intermediate should be synthesized unambiguously and should be similarly analyzed. ~rext, the photochemical reactions should be examined in other solvents. A step further into th:is research would be to confirm the carbonium ion intennediate. This might be done by using optically_ active substituents and checking their rotation before and after photolysis. If the carboniurn ion were indeed the ~Lntermediate, one would expect to see a ra.cemic m·J..x:ture of products. 9 I \ Experimental 1-Methox.ybenzyl bromide. - .3-Methoxybenzyl alcohol (19.74 g, 0.143 moles) and PB:r3 (38.8 g, 0.14.3 moles) were comM.ned in a method reported by Streitwieser and Wolfe5. The crude product was extracted with ether and washed 5 times with a. saturated solution of NaHC03 to remove acid. ~he pure product was then obtained in $2.5% yield from distillation: bp 143-145° (760 mm) (lit. 5 76.5-7!5.0° (7 mm)); nmr (Ccl4) cf J.6o (s,3), 4•28 (s,2), and 6.56-7.25 (m,4) • .3.-Benzylanisole.. - 3-Methox:ybenzyl bromide (1.68 g, 0.00~6 moles) and AlC13 (l.92 g, 0.144 moles) in 40 ml of dry benzene (35.l g, 0.450 moles) 6: gave the product in 71.2't yield using a method in Vogel bp 133-136° (l.00-2.25 mm) (lit.11050 (0.65 mm); ir (neat) 1120 cm-1, 1035 cm-1, and 692 cm-1; nmr (cc14) cf 1.50 (s,3), J.?9 (s,2), 6.44-6.74 (m,3), and 6.~6- 7e22 (m,6). 1.5-Dim.ethoxybenzoie acid, _ 3,5-Dinydroxybenzoic acid (25.0 g, 0.160 moles) and dimethyl sulfate (00.0 g, o.640 moles) were stirred in 300 ml of a 2·08 ~ NaOH solution for 30 min. The crude product was extracted with ether and washed 3 times with 2}-f Na.OH. The pure product was obtained in a 76.41, Yield t~om recrystallization from a J:l mixture of water and methanol: mp 17 1 -1 -l 4-180° (lit.7 184-1B6°); ir (KBr) 1?20 cm-, 1220 cm , and 1170 cm ·; nrnr (acetone) rf 3. eo ( s ,6), 6. 57-6. 73 ( t ,1), and 7 .08-? .20 ( d,2). 1a5-Dimethoxybenzoic acid chlorlde,,;s. - 3,5-Dimethox:ybenzoic acid (20.0 g, o.110 moles) and soc12 (26.2 g, o.220 moles) were refluxed in benzene 10 for 2 hr. The pure product was obtained in 97.1% yield from distillation: bp 135-139° (3025-3.70 nun); ir (neat) 1760 cm-land lack of absorption between JB00-3100 cm-1; nmr (cc14) cf 3.00 (s,6), 6.62-6.00 (t,l), and 7.14-7.27 (d,2). 3..2,-Dimethoxybenzyl alcohol, - 3,5-Dimethoxybenzoic add chloride (2o.4 g, 0.102 moles) and LiAlH4 (6.0 g, 0.162 moles) were refluxed in anhydrous ether for 45 hr. To remove excess LiAlH4, 100 ml of H20 was added. Ammonium chloride was added until the solution became clear. The layers were separated and the ether layer was washed 3 times wUh H20 and then dried w:i.th Mgso4• The ether was stripped off and the product w 0 -1 as recovered in an 81.7% yield: mp 3S-40; ir (KBr) 3300 cm and lack of ab -i ( ) '" 61'\ ( sorption between 1800-1650 cm ; nmr CDC13 a J .. c·v s , 6) , 4.70 (s,2), 6.4)-6.5~ (t,1), and 6.60-6 .. 76 (d,2). l,5-Dimethox.vbenzyl acetatee _- J,5-Dimetho.x:ybenzyl alcohol (14.0 g, o.os33 moles) and acetic anhydride (16.2 g, 0.159 moles) were combined with 3 drops of cone. H2so4• The product was extracted with ether and washed 5 times with a saturated solution of NaHC03 to remove a.cet:ic acid. The ether was then washed 3 times with H20 and then dried with Mgso4• The pure product was obtained from distillation in 57.7% yield: bp 132-13a0 (o.~-1.3 mm)(lit. l 121.5° (0.4 m)); ir (neat) 1743 em-l and lack of absorption between JB00-3200 cm-1; nmr (GDCl3) d 2.10 (s,3), 3.82 (s,6), 5.13 (s,2), and 6.47-6.76 (m,3) • .1.-~ethoxybenzyl acetate .. _ 3-:rtethoxybenzyl alcohol (10.10 g, 0.07h moles), aceti.c anhydride (l7 .zo g, o.160 moles), and 3 drops of cone. H2so4 11 were st·irre d. until the reaction cooled to room temperature. The product was extracted with ether, washed 5 times with a saturated solution of NaHco 3' washed 3 times wlth H20, and dried with Mg.so4• The pure product was then obtained in 71.7t yield from distillation: bp m-89° (0.55- 0.P,o mm); ir (neat) 1735 cm-1 and lack of absorption between 3000-3100 cm-1; nmr (CDCl3) d 2.00 (s,3), J.76 (s,3), 5.13 (s,2), and 6.~0-7.57 (m,4). ~hotochemical Reactions; The reactants were placed in solvent and then irradiated in a Rayonet Photochemical Reactor containing a circular bank of 16 lamps each emitting maximum radiation of 300 nm .. A sample of each substance Photolyzed was covered with aluminum foil and served as a blank to monitor thermal reactions~ 1.-Metho.xybenzyl bromide. - 3-Metho:xybenzyl bromide (1.49 ~, 0.0074 moles) was placed in 10 ml (P.7 g, 0 .. 113 moles) of benzene with 0.1533 g of hexadecane as a standard. This solution was separated i.nto F?: samples Whi c h were removed and periodically checked on a ~as chromatograph. l-Methoxybenzyl acetate,_ 3-~ethoxybenzyl acetate (0.20 g, 0.0011 moles) and O .30 ~ (0.0039 moles) of benzene were mixerl to~ether in an nmr tube and irradiated for 72.5 hr. The reaction was monitored usin~ an nmr spectrometer about every 20 hr. 3.,5-Dirnethox.ybenzyl acetate,_ _ A _ 3,5-dimethoxybenzyl acetate (0.100 e, C.00047 mol ) d ~50 (O 0109 moles) of benzene were added to an es an 0 • g • n~r tube and irradiated for 170 hr. 12 .l..~-Dimethoxybenzyl acetate. -.B - 3,5-Dimethoxybenzyl acetate (0.250 g, 0.0012 moles) and anisole (0.4BO g, 0.0043 moles) were placed in an nmr tube and irradiated for 70 hr. The nmr spectrometer was used to check the progress of the reaction& 13 ·''•I ._o 0 ...... _- ---~ ... ·· ... 0 - --~--· . \ "·· , I I 0 I ... -=-1··- · ------;----\ I ;... .. i , ; i , .. i .. . g ~,--2-;- -;'.'J l __ __:______:__ : ------~--!' __:.___ .. ----;-~--+---- .. 5 ~ N¥R s-pect rum .of the b I an~ o~- _ : !: • \ _ . . · the-photo~~sirs--reaction qf 1 , \ -: - --: . 3, 5 ... dimetllo:x:ybenzy:Lacet~te · - .. ' I! _ _- i . • b' I . , 1 ! ___ :..: ! ip enzene1• , i _ ~ 1 . .I --,------·.. -- ; - ·--. ,1 • I .. _ ' '. ; i . ' \ -- ~f J= [+J.-=E1"~~T-+---- i·•· j-: . I I . .. ! : ; i .,----=L------1 i __ \.,-- ! _ . .,....~; . ;----"\ F' ) - : -, ci I . ----~ c i. -- r i ~ ;;; , - I : • , ' - --<{·--'~,----·1 ------·---: ---+---·--'------.------;-- --~1 -·.·.. • ! ' ••\\ ---- - L __ ;_ ---- .L. ------~J__ .. .. --1l.. 1_ ·,I 0 •I 11.,-.··_ i, --r- , .T + i + 1- ' ; i -:- t i I . 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I · · ·· ·· ·. - I · ·.I.· · ·· · - -:r: L ' •• • • • • • • • - - - - · · · · · re ct n f- 3, 5- ime ho belzyl - · .. · · - ---- · ;- · · ·-·- · - , @--- i, __ ae1tat __ i be ze e. _ .... _ _1 . _ . -- . I . I . . . . • I I . 1 . . l ' I - - . . .., -- - ... - -- ',-- f- ~z- r J,;- t Q - r--JS-·t t- ·r·-· ----t--ct------0 - 00 I - - - · \ . - I \ · I -- ; \ - - - - . - . - . -- - . . . I l I : .. · I I •• . . -- .. ·- I .... - I l i . . l . . i I ...... - - ' It.------ I 1- 1 · . \ • - ,. . , .. . • • •, -- . -- , • - - . - - .. - --• • ...... - - l . i . - . I l " .. . - I · ·-· . . . - . . .. ; - . ' . - . -· . - l - .. I. - - I. .. - ... . I · i I ..... ·-· • _1 I I . . l I . . . f \\ l- . . '· t . . . I - ·: . - I ' - ·-- - -·--. -· - - . .: - ·. I. I i-11····1·.-·:-··1-l-1 ..' 1<--r·-; l I . . . I ! . . · 1' · . ; 1 ·...... ' ·_. - .. ! . - . \' ------1 - : I - I ·1·· I .. . I .. I •... 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(eds.), D~ctionarv of Organic Compounds, 7. Volume II, New York, Oxford University Press, (1965), PP• 1128. 22