2 f 3 other wi se compl ex si gnal s non fi r st or

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Unformatted text preview: Complex Splitting Patterns Complex [ N+1] r ul e hol ds str i ctl y onl y when: [N+1] 1. J s t o al l nei ghbor s equal , and 1. to 2. ∆ν >> J : fii r st or der patter ns. 2. f 3. Other wi se compl ex si gnal s: non-fi r st or der 3. Other n on-fi 3 mul ti pl ets. m ul 4 1 2 1 δ (H ) > δ (H ) (H (H M ul ti pl ets ar e typi cal of al kyl chai ns: al l δs si mi l ar . si e.g., e.g., One sol uti on: str onger magnet One hii gher fi el d spectr a h (Recal l ν ~ H 0 ), “spr eads out” spectr um, (Recal but J s stay same (fi el d i ndependent ). F or exampl e, what mi ght be non-fi r st-or der at 90 M H z, may r esol ve i nto a fi r st-or der patter n at 300 or 500 M H z. 90 M H z 90 500 M H z 500 Ribonuclease A, 40 MHz Rii bonucl ease A R “Sequential” [N+1] Rule 1st Or der patter ns can be anal yzed f or nei ghbor s wi th di ffer i ng J s. J s shoul d di ffer shoul nei ghbor s. n ei b H c CH H C C CC 3 l l for n on-equi val ent b C l J = 3.6 H z Appl y spl i t sequenti al l y b c CH H C C 3 l b H CC l C l J = 3.6 H z Quar tet of tr i pl ets or tr i pl et of quar tets or ….. ? or J >J : J J 2 CH 3—CH —CH 2— CH 2 t (J ) ? qt qt or tq tq t (J ) 2 J <J : 2 J 2 J I f J s acci dental l y the same: [N+1] r ul e acci [ N+1] J ab = J bc N + 1 ab Rul e Rul Sextet Sextet Sextet Stereocenters and Methylene Groups Stereocenters H Bonded/Acidic Protons: Bonded/Acidic OH, SH, N H V ar i abl e δ (concentr ati on and moi stur e-dependent) Var and no coupl i ng ! no 2 s! V ar i abl e Var δ Recal l CH O H Why? F ast H exchange Why? F ast H exchange (H α and H β t r ade pl aces) (H “decoupl es” h ydr ogens. “ decoupl Coupl i ng i s r estor ed on cool i ng, because pr oton exchange i s “fr ozen” (on the NM R ti me scal e). exchange CH OH OH peak often br oad; di sappear s on addi ti on of D 2O...
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This note was uploaded on 11/11/2009 for the course CHEM 368537 taught by Professor Voldhart during the Spring '09 term at University of California, Berkeley.

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