Course Hero Logo

Lect05H1NMRPartII2021.pdf - CHEM333 ORGANIC CHEMISTRY LAB...

Course Hero uses AI to attempt to automatically extract content from documents to surface to you and others so you can study better, e.g., in search results, to enrich docs, and more. This preview shows page 1 - 8 out of 44 pages.

CHEM333ORGANIC CHEMISTRY LAB1H-NMRPART IIMolecular Structure DeterminationA Companion Course for Sophomore Organic Chemistry StudentsDr. John Koh, Professor Chemistry & Biochemistry
1H-NMRPART IITopics CoveredWhen Proton Coupling Constants aredifferent.JabJacTree/splitting DiagramsCoupling in Alkenes and ArenesKarplus CurveDiastereotopic (enantiotopic andhomotopic) hydrogens.Exchangeable protons on heteroatomsWhen do we observe second order effects.
13C-NMR1H-NMRC CHHHCHHSplitting pattern reflects howmany protons are directlyattached to the carbon atomA TripletSplitting pattern reflects howmany protons are connectedto adjacent carbon atom(s)A doubletA TripletFollows N+1 rule.Often Follows the N+1 rule.
Rules for J-coupling•Nuclei must be chemical shift NON-EQUIVALENT to show (obvious)coupling to each other:1,2-dichloroethane is a singlet•The coupling is mutual:A splits B the same amount as B splits AJAB= JBA•Coupling constants are reported in Hz and will have the same value ondifferent instruments.H2CCH2ClClClHaClClHaHbHa: 3.90 ppm, d (J = 7.1 Hz)Hb: 5.77 ppm, t (J = 7.1 Hz)
Protons in different chemicalstructures have different“coupling constants”(i.e. size of splitting)Bad News:Life gets more complicatedGood News:Splitting tells us moreabout the chemical structure.
CCCHbHcHaHaTurn on HbcouplingTurn on HccouplingJab= JacJabJac1:2:1HaTurn on HbcouplingTurn on HccouplingJab> JacJabJac1:1:1:1
CCCHbHcHaHc'HaTurn on HbcouplingTurn on HccouplingJab> Jac=JacTurn on Hc'couplingJabJacJac'JabJacJac'Doublet of tripletsNote, you get the same patternregardless of order.You customarily describe the splittingwith the larger coupling constant first:doublet of triplets (d,t)Note: Technically I shouldavoid using the “prime”designation fordistinguishing two spineqivalent protons by therules of Pople NMRnomenclature (which wedid not cover).

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 44 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Fall
Professor
KOH
Tags
Chemistry, Jac, Nuclear magnetic resonance, Chemical structure

Newly uploaded documents

Show More

Newly uploaded documents

Show More

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture