Miscellaneous Methods UNIT 14 STRUCTURE ELUCIDATION BY INTEGRATED SPECTROSCOPIC METHODS Structure 14.1 Introduction Objectives 14.2 Molecular Formula and Index of Hydrogen Deficiency 14.3 Structural Information Available from Diferent Types of Spectra Mass Spectrum UV-VIS Spectrum IR Spectrum 1 H-NMR Spectrum 14.4 Structure Elucidation of Organic Molecules 14.5 Summary 14.6 Terminal Questions 14.7 Answers
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  Miscellaneous Methods UNIT 14 STRUCTURE ELUCIDATION BYINTEGRATED SECTROSCOIC MET!ODS St uctu e 14#1Int oduction O$%ecti&es 14#' Molecula (o )ula and Inde* o+ !,d o-en De+icienc, 14#.St uctu al In+o )ation A&aila$le + o) Di/e ent T,0es o+ S0ect a Mass S0ect u) U2ISS0ect u) IR S0ect u) 1 !2NMR S0ect u) 14#4 St uctu e Elucidation o+ O -anic Molecules 14#3Su))a , 14# Te )inal 5uestions 14#6 Ans7e s 14#1 INTRODUCTION  This is the lastUnit o+ this cou se# You ha&e studied in details a$out the theo etical as0ects and thea00lications o+ di/e ent t,0es o+ ato)ic and )olecula s0ect osco0ic )ethods in the ea lie Units# You ha&e lea nt that the )olecula s0ect a contain i)0o tant in+o )ation a$out thest uctu e o+ the )olecule# In this Unit ,ou 7ill lea n that ho7 the in+o )ation a&aila$le + o)di/e ent t,0es o+ )olecula s0ect a can $e used +o the st uctu e elucidation o+ the O -anic)olecules# In this conte*t 7e 7ill use 1 the in+o )ation a&aila$le + o) U2IS8 IR8 !2NMR and)ass s0ect o)et ,# To +acilitate this8 7e 7ould +i st eca0itulate the i)0o tant st uctu alin+o )ation a&aila$le + o) di/e ent t,0es o+ s0ect a and then8 7ith the hel0 o+ 7o 9ede*a)0les8 illust ate ho7 to elucidate the st uctu e o+ a )olecule + o) its -i&en s0ect al data# This Unit8 thus8 ai)s to inte- ate the in+o )ation a&aila$le + o) di++e ent t,0es o+ s0ect al)ethods and a00l, this 9no7led-e to a i&e at the st uctu e o+ a )olecule# In othe 7o ds8,ou 7ill $e a$le to co elate the s0ect al si-nals o+ a )olecule to di/e ent st uctu al units0 esent in the )olecule# Once ,ou unde stand the co elation $et7een di/e ent s0ect al+eatu es and the st uctu e o+ the )olecule8 ,ou can also 0 edict the i)0o tant s0ect al details+o a -i&en )olecule + o) its st uctu e# O$%ecti&es A+te stud,in- this Unit8 ,ou should $ea$le to: ; de+ine and calculate the Inde* o+ !,d o-en De+icienc,8 ; discuss the i)0o tance o+ )olecula +o )ula and Inde* o+ !,d o-en De+icienc, in the st uctu e elucidation o+ an o -anicco)0ound8 ; list i)0o tant st uctu al in+o )ation a&aila$le + o) U2IS8 IR8 1   !2NMR and )asss0ect a o+ a )olecule8 ; co elate the si-nals and thei intensities in di/e ent t,0es o+ s0ect ao+ a )olecule to &a ious st uctu al units 0 esent in it8 ; inte- ate the in+o )ation a&aila$le+ o) di/e ent t,0es o+ s0ect a to elucidate the st uctu e o+ a )olecule8 and 3  St uctu e Elucidation ; 0 edict the s0ect al data +o a co)0ound + o) its st uctu al +o )ula# $,Inte- ated S0ect osco0ic Methods 14#' MOLECULAR (ORMULA AND INDE< O(!YDROGEN DE(ICIENCY =e ha&e )entioned that in this unit ,ou 7ill lea n as to ho7the in+o )ation a&aila$le + o) di/e ent t,0es o+ )olecula s0ect a can $e used to elucidatethe st uctu e o+ a )olecule# It is inte estin- to 9no7 that in addition to s0ect a8 the )olecula +o )ula can also 0 o&ide i)0o tant st uctu al leads# It is8 the e+o e8 7o th7hile to 9no7 a$outthe 9ind o+ in+o )ation a&aila$le + o) the )olecula +o )ula# You 9no7 that the )olecula +o )ula indicates the ele)ents constitutin- the )olecule  The inde* o+ h,d o-en and the nu)$e o+ ato)s o+ each ele)ent 0 esent in it# This can 0 o&ide in+o )ation de+icienc, hel0s us to 9no7 a$out the unsatu ation and>o the in- st uctu es in the )olecule# The in+o )ation can a$outthe nu)$e o+ $e o$tained $, co)0utin- a 0a a)ete called Inde* o+ !,d o-en De+icienc, ?I!D@#It )ulti0le $onds ?i#e# dou$le o t i0le@ o in-s 0 esent in is de+ined as the nu)$e o+ 0ai s o+ h,d o-enato)s that )ust $e e)o&ed + o) the a )olecule# co es0ondin- satu ated +o )ula to -i&e the)olecula +o )ula unde conside ation# Let us lea n a$out it 7ith the hel0 o+ so)e si)0lee*a)0les# In case o+ ethane ?C ! @8 the e a e t7o i#e#8 one 0ai o+ h,d o-en ato)s less thanthat eui ed +o the co es0ondin- satu ated co)0ound ha&in- )olecula +o )ula C ! #!ence8 its I!D 7ill $e 1# Si)ila l,8 +o eth,ne ?C ! @8 the nu)$e o+ h,d o-en ato)s eui ed+o the satu ated h,d oca $on 7ould $e C !  C !  4# !ence8 the nu)$e o+ 0ai s o+ ! ato)sneeded 7ould $e 4>' '# So8 I!D o+ eth,ne is '# ' 4 '  ' ' '  ' ' Let us no7 ta9e the e*a)0le o+ c,clo0 o0ane# =hat is its I!D I+ 7e see the )olecula +o )ula C ! 8 7e +ind that the nu)$e so+ h,d o-en ato)s a e t7o less than that +o the co es0ondin- satu ated ali0hatich,d oca $on8 i#e# 0 o0ane# Thus8 acco din- to ou de+inition its I!D should $e 1# You 9no78that this co)0ound itsel+ does not contain an, )ulti0le $ond o unsatu ation 0e se# Thenho7 do 7e account +o the I!D o+ 1 In this case8 the I!D is due to the 0 esence o+ a in- inthe )olecule# Thus8 a in- cont i$utes to I!D in the sa)e 7a, as a dou$le $ond# Si)ila l,8 7ecan conside the cont i$utions o+ halo-en ato)s and nit o-en ato)s on I!D# Theseconside ations -i&e the +ollo7in- +o )ula +o the co)0utation o+ the inde* o+ h,d o-ende+icienc, +o a )olecule + o) its )olecula +o )ula: .    Nu)$e o+ h,d o-en ato)s '  I!D Nu)$e o+ ca $on ato)s Nu)$e o+ halo-en ato)s Nu)$e o+ nit o-en ato)s ' You)a, note he e that the di&alent ato)s such as o*,-en and sul0hu a e not ta9en intoaccount 7hile calculatin- the I!D# Thus8 +o a co)0ound 7ith the )olecula +o )ula as C ! O8the inde* o+ h,d o-en de+icienc, 7ould $e Fe o as sho7n $elo7: I!D  4   1  3 H 3   'It i)0lies that the )olecule o+ C ! O does not contain an, unsatu ation o a in- st uctu e#=h, donJt ,ou t , to calculate the I!D +o the co)0ounds 7ith )olecula +o )ulas as -i&en inthe +ollo7in- SA5# SA5 1 Calculate the I!D +o the co)0ounds ha&in- the +ollo7in- )olecula +o )ulae:      1 '  4 1 1 4 1  The dete )ination o+ I!D alon-7ithothe tests>data hel0s us to choose $et7een alte nati&e st uctu es 0 o0osed +o an un9no7n co)0ound# 36  Miscellaneous Methods ?a@ C ! ?$@ C ! O ?c@ C ! OKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK##KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK## !a&in- unde stood thei)0o tance o+ )olecula +o )ula in st uctu e elucidation and the )ethod o+ co)0utin- theinde* o+ h,d o-en de+icienc,8 let us no7 ta9e u0 a co)0 ehensi&e account o+ the in+o )ationa$out the st uctu al +eatu es>units o+ a )olecule a&aila$le + o) the di++e ent t,0es o+ s0ect ae*hi$ited $, it# 4 4 3 1  1'  14#. STRUCTURAL IN(ORMATION AAILABLE (ROMDI((ERENT TYES O( SECTRA In this section8 ,ou 7ill lea n a$out i)0o tantst uctu ed in+o )ation a$out a )olecule 7hich can $e o$tained + o) its di/e ent t,0es o+ s0ect a# Let us $e-in 7ith the in+o )ation a&aila$le + o) the )ass s0ect u) o+ a )olecule# 14#.#1 Mass S0ect u)  i@ The )>F &alue o+ the )olecula ion8 M ;   -i&es the )olecula )assand can also $e used +o -ene atin- the )olecula +o )ula ?su$sec# 1.#4#1@#   ; ; ii@ The elati&e intensities o+ M  1 and M  ' 0ea9s can $e elated to the nu)$e and natu e o+ hete o ato)s 0 esent in a )olecule# You 7ould ecall + o) Unit 1. that a t,0ical 0atte n o+ M1 and M' 0ea9s is o$se &ed i+ a chlo ine o $ o)ine ato) is 0 esent in the )olecule# iii@ The odd )olecula )ass is indicati&e o+ the 0 esence o+ a nit o-en ato) in the )olecule#!o7e&e 8 this has to $e +u the con+i )ed $, othe )eans o $, anal,sin- the + a-)entation0atte ns +o the t,0ical nit o-en containin- +unctional - ou0s# i&@ The cha acte istic 0ea9sa isin- + o) t,0ical + a-)entation 0atte ns o+ &a ious classes o+ +unctional - ou0s such as  clea&a-e8 loss o+ s)all )olecules such as ! O8 C ! 8 etc# a e uite use+ul# ' ' 4 &@ Ce tain 0ea9s7hich )a, $e att i$uted to the ea an-e)ent o+ the )olecula ion o its + a-)ents ions also-i&e si-ni+icant st uctu al leads# You a e su--ested to ha&e a eloo9 at the su$section 1.#4#1o+ Unit 1.# Ta$le 1.#' containin- co))onl, lost + a-)ents and sta$le + a-)ent ions o$se &edin the )ass s0ect u) is $ein- e0 oduced he e so as to +acilitate ,ou in the inte 0 etation o+ the )ass s0ect a o+ the e*a)0les $ein- ta9en u0 in the ne*t section# Ta$le 1.#': So)eco))onl, lost + a-)ents and the sta$le + a-)ents in the )ass s0ect u) Co))onl, lost+ a-)ents ( a-)ent lost ea9 o$tained ( a-)ent lost ea9 o$tained #   #  # OC! M # M 13 .   C! .   2 .1 #  #  O! # Cl M # M 16 2 .3 # #  C! C   # O CN M '  . M # 2 4. 3  St uctu e Elucidation ! C C!  #  ' ' # # OC! C! M M ' 2 43 ' . $, Inte- ated S0ect osco0ic Methods   # # # #  C! C! M ' . M 2 P1 'P C!  ' Co))on sta$le ions )>F   &alues Ion )>F  4.  C! .   C O  # #    )>F P1    C! '    # # O  )>F  M 2 1    R C O R C! 14#.#' U2IS S0ect u) i@ An a$so 0tion in theU2IS e-ion o+ the s0ect u)8 i#e#8 the U2IS s0ect u) o+ a )olecule indicates the 0 esenceo+ ce tain +unctional - ou0s that ha&e cha acte istic n Q  8  Q   t ansitions# You )a, e+e to Ta$le '#1 o+ Unit '# These t ansitions a e so cha acte istic that the a$sence o+ a U2ISs0ect u) +o a )olecule eli)inates the 0 esence o+ a nu)$e o+ +unctional - ou0s in the)olecule# ii@ The  and the intensit, o+ the a$so 0tion $ands a e indicati&e o+ the e*tent o+ )a* con%u-ation in the )olecule la -e the 7a&elen-th8 - eate the con%u-ation# You can e+e $ac9 to Ta$le '#' o+ Unit ' +o details o+ the cha acte istic U a$so 0tions o+ &a ious st uctu alunits in the )olecules# 14#.#. IR S0ect u)  You 7ould ecall + o) Unit . o+ Bloc9 1 that the e-ion o+ IR s0ect u) an-es + o) 1  24 c) and the in+ a ed s0ect u) can $e $ oadl,di&ided into t7o e-ions as e*0lain $elo7# 1  i@ The e-ion s0annin- + o) . to 1' c) iscalled the +unctional - ou0 e-ion and includes the st etchin- &i$ ations o - ou0 + euencieso+ co))on +unctional - ou0s# The a$so 0tions in this e-ion 0 o&ide in+o )ation a$out the0 esence o+ cha acte istic +unctional - ou0s# 1  ii@ The e-ion that includes all + euencies$elo7 1' c) is called the +in-e 0 int e-ion and includes )olecula &i$ ations8cha acte istic o+ the enti e )olecule o la -e + a-)ents o+ the )olecule# This e-ion is use+ul+o con+i )in- the identit, o+ a 0a ticula )olecule $, co)0a in- 7ith the s0ect al a$so 0tionso+ its authentic sa)0le# iii@ In addition to the 0 esence ?o e&en the a$sence@ o+ a 0a ticula +unctional - ou08 the anal,sis o+ IR s0ect u) -i&es the +ollo7in- in+o )ation: 1  a@  esence o+ h,d o-en $ondin- in the )olecule ?.'2. c) @ $@ Geo)et , ?cis o t ans@ in case o+ al9enes 3P
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