Cahn-In Gold-Prelog R/S System Revisited: Simplifying Assignment of Configuration in Chiral Compounds

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1 Review Artile imepu Journls Journl of Orgni & Inorgni Chemistry ISSN 7- DOI: 0.767/ Chn-In Gol-Prelog R/S System Revisite: Simplifying Assignment of Configurtion in Chirl Compouns Bijoy Kunu Kml Mnsion, ini Bzr, Gorkhpur, Uttr Presh, Ini Astrt A prtilly useful metho following Chn-Ingol-Prelog R/S system is esrie for estlishing R/S onfigurtion in hirl ompouns. The metho is se on the ft tht in given tetrherl hirl ron sequentil rottion of ny three groups in ny of the four tringulr formts oes not ffet the onfigurtion. This provies n opportunity to rotte the three groups prtiulrly inluing the lowest priority group either in lok- or ntilok wise mnner till the lowest priority group is ehin the plne of the pper n thus viewing the moleule from the front for estlishing R/S onfigurtion. The utility of the metho hs een emonstrte in hirl ompouns involving oth yli n yli strutures ering one/two ron tom. Chn-Ingol-Prelog R/S system revisite: Simplifying ssignment of onfigurtion in hirl ompouns Sequentil rottion of these groups in tringles A (,, ) n C (,, ) in tetrherl hirl ron hve no ffet on the onfigurtion n n e use s metho s in C to ple the lowest priority group t the k (on sh on) n estlish R/S onfigurtion y viewing the moleule from the front. A C okwise rottion of three groups N COO Antilokwise rottion of three groups COO C N C OOC N Sequentil rottion of three groups long ny of the four tringles hs no ffet on the onfigurtion COO N COO N N C C OOC C Convert using sequentil rottion of three groups long the tringles till lowest prioirty group is on the sh on to ssign onfigurtion y viewing from the front. Corresponing uthor: Bijoy Kunu ijoy_kunu@yhoo.om Former Diretor, Kml Mnsion, ini Bzr, Gorkhpur-7 00, Uttr Presh, Ini. Tel: Cittion: Kunu B. Chn-In Gol-Prelog R/S System Revisite: Simplifying Assignment of Configurtion in Chirl Compouns. J Org Inorg Chem., :. Keywors: Stereohemistry; R/S onfigurtion; Chirlity; Chn-Ingol-Prelog R/S system Reeive: July 6, ; Aepte: August 6, ; Pulishe: August 5, Introution The unmiguous ssignment of enntiomers of hirl ompoun is generlly rrie out using Chn-Ingol-Prelog R/S system. The metho involves prioritiztion of sustituents strting from highest tomi numer to lowest followe y ssignment of R n S onfigurtion y pling the lowest priority sustituents t the k []. There re two methos wiely tught to grute stuents to ssign R/S onfigurtions: one tht involves use of moel kits n seon tht involves mentl rottion of moleule. In oth the ses entire moleule is rotte so tht the lowest priority group is t the k n then remining three groups in the orer of priority is exmine either in lok or ntilokwise iretions. Yet nother metho tht is lso use n isusse in severl text ooks involves mentl viewing of the moleule from the reverse sie of the lowest priority group (Figure ). I Uner Liense of Cretive Commons Attriution.0 Liense This rtile is ville in:

2 Journl of Orgni ARCIVOS & Inorgni DE Chemistry MEDICINA ISSN ISSN Figure COO C N Conventionlly use metho to estlish R/S onfigurtion isusse in text ooks. foun tht lthough ll the three methos re tught to grute stuents, lrge perentge of stuents remin wry to these methos n often fil to either unerstn the sis or re unle to extrpolte the methoology to moleules with more thn one hirl enter. This n e minly ttriute to mentl exerise involving visuliztion of hirl moleules to ssign onfigurtion. I opine tht while introuing R/S onfigurtion to grute stuents, n lterntive metho of tehing y rwing strutures inste mentl visuliztion to ress the issue of R/S ssignment my e more enefiil. In this ommunition I isuss simple metho tht involves rwing of itionl flying-wege strutures on pper of the struture in question n then preit the R/S onfigurtion without mentl visuliztion. The ie stems from the presene of four set of tringles in ny tetrherl hirl ron. The ltter in the flying wege projetion omprises two ons present on the plne of pper, one wege on ove the pper n sh on going elow the plne of the pper (Figures n ). A lose exmintion of the tetrherl struture revels tht t ny given time, four tringles n e forme y onneting the three groups tthe to the hirl ron (Figure ). Out of the four tringles: A omprises groups,, ; B omprises groups,, ; C omprises groups,, n D omprises groups,,. I rgue tht three sustituents in the tringle B with priority from (Figures A n ) when ple in irulr formt, n e sequentilly rotte long the periphery either lokwise (Figures B n ) or ntilokwise (Figures C n ) without ffeting its onfigurtion. It is pertinent to mention tht the presene of single on etween the hirl ron n the sustituent (Figures A n ) llows one to rotte this on. Inee, the epition of tetrherl ron A with tringle B lso provies ottom view of the ompoun whih in turn will provie grute stuents with etter unerstning with regr to the orienttion of four ons in ny tetrherl ron in D spe. We then exmine the onfigurtion in A/B/C n s expete, the iretion of priority from remine lokwise in ll the three situtions leing to the ssignment of R onfigurtion (Figure ). In other wors ssignment of R or S onfigurtion with sequentil rottion of sustituents long the tringle is not ffete. This lso provies n option to ssign onfigurtions in B n C y simply trnsforming them to A y sequentil rottion of three groups long the tringle in either iretions n then looking t the moleule from the front to exmine the iretion of priority from. The ove lterntive metho for the ssignment of onfigurtion ws emonstrte y using lnine s moel hirl ompoun y mintining the iretion of priority of funtionl groups (N ) (COO) (C ) s in A using tringulr formt B. Aoringly, N funtionlity is ple on, is reple with COO n is reple with C. The resulting flying wege struture A (Figure ) ws exmine using moleulr moel kit whih exhiite R onfigurtion. Now ntilokwise sequentil rottion of the sustituents N, COO n C long the tringle B y holing the group will furnish flying wege struture B (Figure ) wheres lokwise sequentil rottion of N, COO n C will furnish flying wege struture C (Figure ). Grtifyingly, oth B n C espite sequentil rottions of funtionl groups in either iretion long the tringle B exhiite R onfigurtion. Next, the ove lterntive metho for the ssignment of onfigurtion ws further emonstrte y using -lnine (A) A Figure Figure B B Figure B C Four tringles A, B, C n D in tetrherl hirl ron. okwise rottion of groups (,, ) A D Antilokwise rottion of groups (,, ) Sequentil rottion of sustituents long the tringle B oth in lok n ntilokwise formt in tetrherl ron retine R-onfigurtion. N Anti-lokwise sequentil rottion of three groups exept the group COO N C COO A okwise sequentil rottion of three groups exept the group OOC Sequentil rottion of the three sustituents N, C n in Alnine (A) long the tringle B oth in lok n ntilokwise formt retine the R-onfigurtion. C C C N This rtile is ville in:

3 Journl of Orgni ARCIVOS & Inorgni DE Chemistry MEDICINA ISSN ISSN s moel sustrte. Using the flying wege projetion involving tringle B, -lnine A ws rwn y eliertely pling COO funtionlity on (lterntively one n reple with / C /N to rw flying wege projetion of -lnine (Figure S), while hs een reple with, hs een reple with C n hs een reple with N funtionlity (Figure 5). Now ntilokwise sequentil rottion of the sustituents N, n C long the tringle B y holing the COO group will furnish flying wege struture B wheres lokwise sequentil rottion of N, n C will furnish flying wege struture C. We then exmine the onfigurtion of A, B n C using moleulr moel kit n s expete grtifyingly ll the three flying wege strutures espite sequentil rottion of three sustituents exhiite S-onfigurtion. This implies tht if one hs to ssign R/S onfigurtion in given flying wege struture, the three groups n e sequentilly rotte in tringulr formt in either iretions till the lowest priority group is on the sh on. This then provies option to the viewer to exmine the onfigurtion s in C y iretly looking from the front without pplying the onventionlly use metho of mentl visuliztions. Thus to estlish onfigurtions of A n B, one n trnsform them to C y pling the lowest priority group hyrogen k n view the moleule from the front. The exerise ws then repete one y one for the remining three tringles A, C n D (Figure ) where one group ws hel sttionry n remining three sustituents were rotte sequentilly long respetive tringles. (Figure S) s envisge no evition ws oserve from S-onfigurtion espite sequentil rottion of sustituents long the tringles. I further oserve tht even multiple sequentil rottions of sustituents long the tringles i not ffet the onfigurtion (Figure S). It is noteworthy tht for given hirl tetrherl ron ompoun suh s -lnine, mximum of flying wege strutures se on tringles A, B, C n D. One n esily rw these flying wege strutures y sequentil rottions of groups roun the four tringles without othering out heking the onfigurtions (Figures S n S5). To the est of my knowlege, till te this informtion of rwing mximum of flying wege strutures with retention of onfigurtion for hirl ompoun with n symmetri entre is not ville in the literture. Out of only flying wege strutures hve lowest priority group on the sh on. In orer to further prove the generl ppliility of the metho for estlishing onfigurtion, the metho ws extene to two ron yli hirl ompouns. For this S, S-ihloroutne 5A ws initilly selete s moel sustrte (Figure 6). In the first instne, the three sustituents were rotte sequentilly on eh of the hirl rons till on oth the hirl rons ws on the sh line s in 5B. The onfigurtion of 5B with lowest priority group on the sh on for the oth the rons ws then ssigne y simply looking from the front whih ws lso onfirme using moleulr moel kit n s expete 5B to exhiite S, S onfigurtion. I further sequentilly rotte the three sustituents on either of the hirl rons oth in lokwise n ntilokwise iretion to generte strutures Uner Liense of Cretive Commons Attriution.0 Liense 5C n 5D. Moleulr moel kits for oth 5C n 5D onfirme tht sequentil rottion of three sustituents in given flying wege struture either in lokwise or ntilokwise iretions i not h ny ering on its R or S onfigurtion. Thus, in given sitution, R/S onfigurtion in either of the three strutures 5A/5C/5D n e ssigne y onverting them to struture 5B y sequentil rottion of sustituents long the tringle. Similrly, the onfigurtion of R, S-ihloroutne in 6A (Figure 7) ws ssigne following sequentil rottion of sustituents long the tringle for one of the rons only till the ws ple on the sh on s in 6B (Figure 7). For the seon ron, the ws lrey ple on the sh on. Next, looking t oth the rons in 6B from front onfirme the presene of R n S onfigurtions. In further stuies the struture the sustituents in the seon ron 6B ws sequentilly rotte to stuy effet on onfigurtion. The resulting struture 6C (Figure 7) ws exmine using moleulr moel kit whih onfirme the presene of R n S onfigurtions. Finlly, the utility of the metho emonstrte in yli struture -isopropylylohexn--one 7 hving hirl ron in ring N Figure 5 COO B Figure 6 Anti-lokwise sequentil rottion of three groups exept the COO group C COO A okwise sequentil rottion of three groups exept the COO group C N COO N Sequentil rottion of the three sustituents N, C n in -Alnine long the tringle B oth in lok n ntilokwise formt retine the S-onfigurtion. C C C C 5A 5B 5C 5D S, S-ihloroutne: sequentil rottion of sustituents, C n long the tringle oth in lok n ntilokwise formt retine the S-onfigurtion. C C C C 6A 6B 6C Figure 7 R, S-ihloroutne: sequentil rottion of sustituents, C n long the tringle oth in lok n ntilokwise formt retine S n R onfigurtions. C

4 Journl of Orgni ARCIVOS & Inorgni DE Chemistry MEDICINA ISSN ISSN (Figure 8). Sine in the yli struture, the four sustituents re ple in mnner tht they nnot e move in tringle sequene s emonstrte ove. In this sitution, the four sustituents n e numere strting from numer for the highest priority group n numer to the lowest priority group. Next, inste sustituents only the numers n e rotte long the tringle in sequentil mnner till the lowest numer is on the sh line (Figure 8). Finlly, one n view the moleule from the front n estlish the R/S onfigurtion y simply moving from priority numer to. Thus, using this metho one n esily ssign R onfigurtion to the struture 7. Inee in some of the exmples isusse ove where the lowest priority group is on the wege on, one n ssign R/S onfigurtion y pplying the onventionl rule of reversing the oserve iretion of the priority se on tomi numers. The metho esrie here is more prtil n remins pplile in ll situtions n involves sequentil rottions of three groups long the tringle till the lowest priority group is on the sh on (ehin the plne of pper). The R/S onfigurtion n then e ssigne y looking t the resulting moleule from the front inste rotting the moleule mentlly or using moleulr moel kits. The four tringles A, B, C n D on one hn n e use to emonstrte tht sequentil rottion of groups in the respetive tringle hve no ffet on the onfigurtion, on the other hn ny one of the tringles A, B n C n e hosen to ssign R/S onfigurtion in given hirl ompoun y pushing the lowest priority group on the sh on following sequentil rottions. The R/S onfigurtion n then e ssigne y simply looking from the front of the moleule for the iretion of priority from highest to lowest tomi numers. Figure 8 7 C O Conlusions R-onfigurtion -isopropylylohexn--one: Sequentil lokwise rottions of sustituents, n long the tringle in the form of numers ( to se on priority) llotte to eh group retine the R-onfigurtion. In summry, prtil metho involving sequentil rottion of ny of the three out of four groups in ny of the four tringulr formts in tetrherl hirl ompoun n e pplie for estlishing R/S onfigurtions. In other wors in ition to onventionlly use metho se on mentl exerise, n lterntive metho involving sequentil rottions of ny three groups in tringulr formt will provie itionl option for ssignment of R/S onfigurtion. Aknowlegements I m thnkful to Sengupt SK, e of the Deprtment, Deprtment of Chemistry, DDU University, Gorkhpur, Uttr Presh, Ini for inviting me s visiting fellow to teh R/S onfigurtion to grute stuents. This rtile is ville in:

5 Journl of Orgni ARCIVOS & Inorgni DE Chemistry MEDICINA ISSN ISSN Referene Chn RS, Ingol CK, Prelog V (966) Speifition of Moleulr Chirlity. Angewnte Chemie Interntionl 5: 85. Uner Liense of Cretive Commons Attriution.0 Liense 5