lec 9 - Sec$on 1.5 Interpre$ng Mass Spectra CHM3122...

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Sec$on’1.5:’Interpre$ng’Mass’Spectra’ CHM3122’ 1’ Interpreta$on’of’mass’spectra’
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molecular’ion’ m/z’=’32’ in’EI,’the’ simplest’ process’ is’the’ ejec$on’of’an’ electron’ from’the’ molecule’to’ create’the’ radical’ca$on’M •+ example’:’CH 3 OH’+’e - ’CH 3 OH •+ ’+’2e -’ aJerwards:’bond’ cleavage’ CH 3 OH •+’ ’CH 2 OH + ’+’H ’m/z’31’ CH 3 OH •+’ ’CH 3 + ’+’ OH’ ’ ’m/z’15’ CH 2 OH + ’CHO + ’+’H 2’ m/z’29’ Interpre$ng’EI’mass’ spectra’ CHM3122’ 2’ Interpreta$on’of’mass’spectra’
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The’molecular’ion’peak’ this’peak’will’be’prominent’for: aroma$cs’>’ conjugated’ alkenes’>’ cyclic’compounds’>’ organosulfur’compounds’>’short’ linear’ alkanes’>’mercaptans this’peak’will’oJen’be’seen’for: ketones’>’amines’>’esters’>’ ethers’>’ carboxylic’ acids’~’ aldehydes’~’amides’~’ halogenates’ this’peak’will’usually’not’be’seen’for: alipha$c’ alcohols,’nitrites,’nitrates,’ nitrated’ deriva$ves,’nitriles,’ highly’ branched’ alipha$cs’ CHM3122’ Interpreta$on’of’mass’spectra’ 3’
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Iden$fying’the’M + ’peak’ problem:’some$mes,’EI’doesn±t’show’the’M + ’peak ’ solu$on:’ use’chemical’ioniza$on’(CI) ’ ’ CHM3122’ Interpreta$on’of’mass’spectra’ 4’ CI’ spectrum’ molecular’ ion’ molecular’ formula’ EI’spectrum’ fragmenta$on’ structure’
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The’Nitrogen’Rule’ ’ ’ ’A’ molecule’ with’an’ even’ molecular’mass’must’ contain’ either’ zero’or’ even’ number’of’ nitrogen’ atoms;’an’ odd’ molecular’mass’ indicates’an’ odd’ number’of’ nitrogen’ atoms’ applies’to’all’ organic’compounds’ containing:’ C,’H,’O,’N,’S,’F,’Cl,’ Br,’I,’P,’B,’Si,’As,’… you’must’use’ atomic’masses rounded to the nearest whole number CHM3122’ Interpreta$on’of’mass’spectra’ 5’
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Nitrogen’Rule’Examples’ 1. Pyridine’has’a’ molecular’mass’of’79’ Da.’ ODD’ mass =’ odd’ number’of’N’ atoms’ 2.’ Benzene’has’a’ molecular’mass’of’78’ Da.’ EVEN mass =’ even’(or’ zero) number’of’N’ atoms’(0)’ 3.’Pyrimidine’has’a’ molecular’mass’of’80’ Da.’ EVEN mass =’ even’(or’ zero) number’of’N’ atoms’(2)’ CHM3122’ Interpreta$on’of’mass’spectra’ 6’
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High’resolu$on’molecular’ion’peaks’ CHM3122’ Interpreta$on’of’mass’spectra’ 7’ Molecular ion m/z 250’ 250’ Table 1.4: Exact masses 250.1934’ 250.1808’ Appendix A C 16 H 26 O 2 C 15 H 24 NO 2
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Index’of’Hydrogen’DeFciency’ measure’of’the’degree’of’unsatura$on’
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lec 9 - Sec$on 1.5 Interpre$ng Mass Spectra CHM3122...

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