Mass spectra of liquid crystals. V.Cyclohexyl and phenyl esters of cyclohexanecarboxylic and benzoic acids

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1 Mass spetra of liquid rystals. V.Cylohexyl and phenyl esters of ylohexanearboxyli and benzoi aids Citation for published version (APA): Lelerq, P. A., & Bogaert, van den, H. M. (). Mass spetra of liquid rystals. V.Cylohexyl and phenyl esters of ylohexanearboxyli and benzoi aids. Organi Mass Spetrometry, (),. DOI:.0/oms.0 DOI:.0/oms.0 Doument status and date: Published: 0/0/ Doument Version: Publisher s PDF, also known as Version of Reord (inludes final page, issue and volume numbers) Please hek the doument version of this publiation: A submitted manusript is the version of the artile upon submission and before peerreview. There an be important differenes between the submitted version and the offiial published version of reord. ople interested in the researh are advised to ontat the author for the final version of the publiation, or visit the DOI to the publisher's website. The final author version and the galley proof are versions of the publiation after peer review. The final published version features the final layout of the paper inluding the volume, issue and page numbers. Link to publiation General rights Copyright and moral rights for the publiations made aessible in the publi portal are retained by the authors and/or other opyright owners and it is a ondition of aessing publiations that users reognise and abide by the legal requirements assoiated with these rights. Users may download and print one opy of any publiation from the publi portal for the purpose of private study or researh. You may not further distribute the material or use it for any profitmaking ativity or ommerial gain You may freely distribute the URL identifying the publiation in the publi portal. If the publiation is distributed under the terms of Artile fa of the Duth Copyright At, indiated by the Taverne liense above, please follow below link for the End User Agreement: Take down poliy If you believe that this doument breahes opyright please ontat us at: openaess@tue.nl providing details and we will investigate your laim. Download date: 0. Apr. 0

2 ORGANIC MASS SPECTROMETRY, VOL., () Mass Spetra of Liquid Crystals V.? Cylohexyl and Phenyl Esters of C ylohexanearboxyli and Benzoi Aids P. A. Lelerqt Laboratory of Instrumental Analysis, Eindhoven University of Tehnology, P.O. Box, 00 MB Eindhoven, The Netherlands H. M. van den Bogaert Philips Researh Laboratories, PO Box 0OO0, 00 JA Eindhoven, The Netherlands The 0 ev eletron impat mass spetra of ylohexanearboxylate and benzoate derivatives are presented. This part inludes data on six substituted ylohexyl and derivated phenyl esters, inluding eleven alkoxyphenyl and diyanoalkoxyphenyl esters. d on the observed peak shifts by various substituents, the elemental formulae of the main fragment ions are rationalized. INTRODUCTION Liquid rystals have been the subjet of onsiderable study during the last deade. Suh ompounds, blended in multiomponent mixtures, have found extensive appliation in optoeletroni devies suh as liquid rystal displays (LCDs). Surprisingly, there are only a few reports on the mass spetrometry of these ompounds. In this paper, the mass spetra of various lasses of esters are presented. Eah lass has different material properties whih are used to tune the nemati phase of LCDs for speifi appliations. Cylohexyl ylohexanoates (lass I) are esters with small optial anisotropy. These lowbirefringene materials inrease the viewing angle of LCDs. Class I esters have found wide use beause of their low visosity and their wide nemati temperature ranges. The,diyanophenyl esters of lasses I and IV have strong negative dieletri anisotropy. These omponents are used in eletrially ontrolled birefringene (ECB) LCDs. The ECB LCDs offer higher ontrast, a wider viewing angle and a more stable grey sale than twisted nemati (TN) displays. Fluorinated phenyl benzoates (lass V) are applied to derease LCD response times. The mass spetra of the five lasses of esters are ollated in Tables. In the disussion of the spetra the 'peak shift tehnique' is employed to dedue the nature of the various fragment ions. In this tehnique, use is made of the shifts in m/z values by different substituents within a lass of ompounds. It should be emphasized, however, that the ion strutures given are not to be taken literally, beause aurate mass measurements were not arried out. EXPERIMENTAL Gas hromatographi/mass spetrometri analyses were arried out under onditions reported previously.' For t For Parts I and IV. see Refs. and. Author to whom orrespondene should be addressed 00)/ /00 $ by John Wiley & Sons, Ltd. the determination of the moleular masses of the various esters, positive ion hemial ionization mass spetra were aquired on a Finnigan 000 quadrupole instrument (Finnigan, San Jose, CA, USA). Methane and ammonia were used as reagent gases. ~ ~~ RESULTS AND DISCUSSION The mass spetra of six alkylylohexyl esters of alkyl(bi)ylohexylarboxyli aids (lass I) are ondensed in Table. Class I Class I I To our knowledge, none of these spetra have been reported previously. Moleular ions are absent in all instanes. The only peaks indiative for R are found at m/z ( + R), orresponding to the oddeletron alkylylohexene ions [CH,R] +.. The heaviest ions found in the mass spetra of these ompounds are from the protonated free aids, [R'C,H,,C(OH),]+ at m/z ( + R'). These ions lose one and two moleules of water, resulting in peaks at m/z ( + R') and ( + R'), respetively. Loss of CO from the arbonyl ation at m/z ( + R') leads to peaks at m/z ( + R') from the alkylylohexyl ions [RCHIO] +. The spetra of the ylohexyl esters are dominated by abundant lowmass ion series. The eletron impat (EI) spetra of substituted phenyl esters of (bi)ylohexylarboxyli aid derivatives (lass ) are listed in Tables. The mass spetrum of has been published before.' The spetrum of the pentoxyphenyl ester of propylylohexane arboxyli aid, a homologue of and, has also been rep~rted.~ The origin of two to six harateristi ions in the spetra of was rationalized previously, Reeived August Revised manusript reeived November Aepted November

3 MASS SPECTRA OF LIQUID CRYSTALS. PART V Table. Relative abundanes of harateristi ions in the EI mass spetra of ylohexanearboxyli aid ylohexyl ester derivatives (lass I)' No R' R RMM +R' +R' +R' +R' +R' +R 0 0 ' X" 0 ' Y 0 " X" 0 0 Y No. peakb " =npropyl, =nbutyl, =npentyl, C,H,,= "m/z of base peak. CX=C,H,o,Y= C,H,~. *Coinides with m/z. Inluding isotopi ontribution of m/z ( + R)..ylohexyl. Table. Relative abundanes of harateristi ions in the EI mass spetra of ylohexanearboxyli aid phenyl ester derivatives (lass )' No. R' HP R) F F Me RMM 0 M" + R' + R' miz +R' +R' +A' No a Me = methyl, = npropyl, = nbutyl, = npentyl. "m/z of base peak. "A=(CH,ompounds) or (F,and). peakb 0 0 and their masses have been These literature data are in agreement with our findings and support the struture assignments to the main fragment ions. With the exeption of the biylohexylarboxyli aid esters, the moleular ions are present in all instanes, albeit with low abundanes. In the spetra of and, peaks at m/z ( + R') from [R'CHIoCO]+ are higher than those in the spetra of the ylohexyl esters, whereas these peaks are vir tually absent in those of the alkoxyphenyl esters. Oddeletron ions u lower in mass are found exlusively in the spetra of the alkylphenyl esters (Table ). The ions [HOCHRZ]+' are responsible for the base peaks at m/z ( + R) in the spetra of the alkoxyphenyl esters (Table ). These spetra also ontain large peaks at m/z, orresponding to [HOC,H,OH] +*, whenever the alkoxy group is larger than methoxy. Similarly, tropylium ions [HOC,HCH]+ ause peaks at m/z in the spetra

4 P. A. LECLERCQ AND H. M. van den BOGAERT Table. Relative abundane of harateristi ions in the EI mass spetra of ylohexanearboxyli aid alkoxyphenyl ester derivatives (lass )' m /z No. R' R' RMM M+. +R' +R +R' peak" 0 PI OH OMe OMe OMe O O O 0 O O a d Od ' a Me = methyl, = ethyl, =npropyl, =nbutyl, =npentyl. brn/z of base peak. See m/z ( + R). Inluding isotopi ontributions of peaks at u less. 0 a 0 0 Table. Relative abundanes of harateristi ions in the EI mass spetra of biylohexylarboxyli aid phenyl ester derivatives (lass )' mlz No. R' R RMM +R' +R' +R' X F 0 ' F 0 0 Z" a mil No. peakb 0 a a = npropyl, = npentyl, C,H, =,ylohexyl. bm/z of base peak. "X = C,H,,, = C,H,,. of the alkylphenyl esters. Alkylylohexyl ions [R'CHlo]+ give peaks at m/z ( + R'), whih are higher in the spetra of and than in those of the alkoxyphenyl () and alkylylohexyl esters (). Abundant lower mass ions are found in the spetra of esters and. while the orresponding peaks are less intense in those of the alkoxyphenyl esters. The spetra of the biylohexylarboxyli aid phenyl esters (Table ) ontain yloalkyl and ylo x C ' f d alkenyl ions up to m/z ( + R'). The fluorophenyl esters and produe additional ions by the loss of H,O from [R'CHloCO]', resulting in small peaks at m/z ( + R'): m/z (%) and (%), respetively (not inluded in Table ). New EI mass spetra of eleven alkoxy,diyanophenyl esters of alkylylohexylarboxyli aids (lass ) are presented in Table. The spetrum of the pentyloxydiyanophenyl hexylylohexanoate is also shown in Fig.. 0 m/z Figure. 0 ev El mass spetrum of the.diyano (pentyoxy)phenyl ester of hexylylohexanearboxyli aid ()

5 MASS SPECTRA OF LIQUID CRYSTALS. PART V Class V Class IV R Moleular ions are absent, or have abundanes < %. aks at m/z ( + R'), orresponding to ions [HOCH,(CN),0R] +', are small. This ontrasts strikingly with the spetra of the (unsubstituted) alkoxyphenyl esters (Table ), where the orresponding phydroxyphenylalkyl ethers represent the base peaks. The peaks at m/z ( + R') and ( + R'), however, are muh larger than in those spetra. These peaks again orrespond to the ions [R'C,H,,CO]+ and [RCH] +, respetively. The latter is aompanied by a peak from the alkylylohexene ions [R'C,H,]+' at m/z ( + R'). aks at m/z 0 are harateristi of alkoxydiyanophenyl esters, and arise from the ions [HOCH,(CN),0H] +'. The ethoxyphenyl derivatives, and also yield peaks at m/z, while these peaks are ompletely absent in the spetra of the other ompounds. This phenomenon is not easily rationalized. Lower mass yloalkyl fragment ions are abundant. aks harateristi of R' are found at m/z (R' = and Hx), (R' = ) and (R' = ). The hexylylohexanoate derivatives also give peaks at m/z and, while peaks at m/z,, and are larger in the spetra of than in those of ompounds with R' <. The underlying fragmentation mehanisms are not yet understood. The EI mass spetra of six alkoxydiyanophenyl esters of alkylylohexylbenzoi aids (lass IV) are ondensed in Table. Mass spetra of these esters have not been published, but the ourrene of very stable arbonyl ions as base peaks in the spetra of some alkylbenzoates and alkylylohexylbenzoates has been reported.'*' In agreement with these findings, peaks at m/z ( + R'), orresponding to [R'CHloCHCO]C, represent about 0% of the total ion urrents. Moleular ions, and ions [HOC,H,(CN),OR'] +', are ompletely absent. aks at m/z 0, however small, are harateristi of these esters, as desribed for S. Again, peaks at m/z are found exlusively in the spetra of the ethoxyphenyl esters and. Ions of m/z and ome from ~ ~~ ~ ~ ~~ Table. Relative abundanes of harateristi ions in the EI mass spetra of alkylylohexylarboxyli aid diyanoalkoxyphenyl esters (lass )' No. R' Hx Hx Hx R BU RMM t R' + R R' +R' +R' " " No peakb

6 ~~ ~ P. A. LECLERCQ AND H. M. van den BOGAERT Table. Relative abundanes of harateristi ions in the EI mass spetra of alkylylohexylbenzoi aid diyanoalkoxyphenyl esters (lass IV)' No R' R RMM +R' +R' 0 peak" BU 0 BU BU 0 0 a =ethyl, =nbutyl, =npentyl bmjz of base peak. Table. Relative abundanes of harateristi ions in the El mass spetra of various benzoi aid phenylester derivatives (lass V)' mlz +R No R' R' R RMM +R' +R +R' +A CN H 0 " CN H 0 d 0 CN F 0 0 Me0 H 0 I YO' F H 0 0 X' F l X" CN F 0 X" " H 0 Ye Z' H 0 mh No 0 peakb _ 0 * Me = methyl, = ethyl, = npropyl, = npentyl, C H =.phenyl, C H, =.ylohexyl. I, m jz of base peak. 'A= (CH,,ompounds,0) or (OH.and). See m/. ( + R'). "X = C,H,,, Y = C,H,,, Z = C,H,CN [HC=CHCH,CO]+ and [H,C,C,H,]+. The nature of the remaining ions listed is evident. New mass spetra of various (bi)phenyl esters of (ylohexy)benzoi aid derivatives (lass V) are given in Table. Moleular ions are not present, or have abundanes < % (, and ). In agreement with the literature ited above,"' the arbonyl ions [R'C,H,CO]+ give the base peaks at m/z ( + R'), exept in the spetrum of, whih shows the base peak at m/z, orresponding to the ion [HOC,H,CO]+. The ourrene of abundant phydroxyphenylarbonyl ion peaks in the spetra of a few alkoxybenzoates has been In the spetra of the alkyl(ylohexy)benzoates and 0, [HCC,H,CO)+' ions at m/z are found with low abundanes. The ester group appears as [HOC,HRR]+' at m/z ( + R + R) in most of the spetra. Ions [R'C,H,]+ at m/z ( + R') appear only in the spetra of the alkylbenzoates, while peaks at m/z are only found for alkylylohexylbenzoates. REFERENCES. P. A. Lelerq and H. M. van den Bogaert, Org. Mass Spetrom.. R. L. Hubbard, in oeedings of the Symposium on the,0 (). Physis and Chemistry of Liquid Crystal Devies, ed. by G. J.. J. Cermhk, I. Kolb and I. Nhdherna, Chem. um., 0 Sprokel, p., Plenum, New York (). ().. P. A. Lelerq and H. M. van den Bogaert, Org. Mass Spetrum.. T. I. Martin and W. E. Haas,Anal. Chem., A ()., ().. H. J. Deutsher, M. Shierhorn, G. Kraus and H. Remane, Fresenius'z. Anal. Chem., ( ).