Notation for Spin Systems Capital letters A, B, C, M, A, X, Y,....... ^Same letter = same chemical shift (A3, B2, X6,____) ^Different letters = different chemical shifts Letters close in the alphabet (A, B, C, ...) J [Hz] of the same magnitude as Av [Hz] Letters separated in the alphabet (A, M, Xv..) large separation of chemical shifts -different nuclei (XH, 31P, 195Pt,...) -same nuclei but Av [Hz] much larger than J !! Av [Hz] depends on B0!! Notation for Spin Systems ^Different letters = different chemical shifts Notation for Spin Systems Two situations: a) Complete equivalence = Chemical shift equivalence (isochronous nuclei) + magnetic (spin-coupling) equivalence (isotachous) Magnetic equivalence = each member of one group of spins is coupled equally to all members of any other group ^2-^25 ^2^2v • •• Notation for Spin Systems b) Chemical shift equivalence, magnetic INequivalence AA'BB', AA'XX', AA'A"XX'X",.... Magnetic Inequivalence Bracket Notation Square brackets with subscript indicate repeate symmetry-related magnetically inequivalent groups of nuclei, e.g. [AB]2 Square bracket without subscript indicate magnetic equivalence of isochronous nuclei inside, e.g. [A6] Each bracket represents a specific symmetry operation (see anthracene) Append a point group symbol to avoid ambiguity Free rotation - apply Mortimer rule = the most symmetrical conformer Notation for Spin Systems BB'AA'CC'A"A"'B"B"' VI Notation for Spin Systems Ring plane [[A]2B]2 / \ Plane perpendicular to ring considering isotope shift: A[BC]2DX 12 Spin Systems in JH NMR [AB]2C AA'BB'C [Afv1]2X O /C=C- A3 H AB H AX H 1 rS V s> i H [AB]2 [AX]2 When separated by more than 3 bonds, the spin systems can be considered separately (with exceptions) 13 AA'A"XX'X" AB2XY2 3JPH(cis) = 10-40 Hz 3JPH(trans) = 80 - 150 Hz 14 15 Spin Systems AB System The simplest higher-order spin system Spin-spin coupling AB System AB AB Av AB B J J Av AB 'AB AB Av AB AVal »1 I AB Av >1 Av <1 Hi ttfi -HjK 1 marks the chemical shifts Increasing Frequency 20 ABX Spin System JAB=V2-Vl=V4-V3=Vt -v5=vs-v J AX + J BX ~ V12 V9 AvAD = v, -v AB _ 1 A B l — 9 (jAX jRX ) BX N — 9 {j Av + j by ) AX BX A VfB =^AB+L = V^-^lX^"^) Midp — \ (yA +vB) + jN A vSOT = A - L = ^(v8-v5)(v7-v, Midp = \{v A+v B) - X Part of the ABX Spin System 12 11 10 9 j AX j BX n = l(j -iy 2 ^ AX 15 14 12 BX Both part A and part X feature the same multiplet symmetrical about VA or vx Both parts have 12 lines with a center of symmetry at vA or vx Spin System \k = j AÄ + j XX' \m ~ j AA • ~~ j xx} \n ~ j AX + j AX' L = ~ j AX ' ~^AX} AA'XX' Spin System AA'XX' Spin System Vl,2 - ^3,4 = j ax j ax jaa' ~*~ jxx = v9-v10=vn-v12 = VOö - ^7 )(V5 - ^8 ) = V< V9 - V12 )(YlO ~ Vl 1) ^3,4 -*5+6+7+8 A 2 _ v10-vn .^6-^7 *7 9+10+11+12 H3C-P-M-P-CH3 28 29 0 —'-'-1-1-'-1-1- -59 -60 d Figure 7. l9F NMR spectra of (CF3)3BCO (left), [(CF3)3BC(0)OH]- (light) and [(CF3)3BC02p- (top). —I—I—I—I—I—I—I—I—I—I—I- -16 -17 -18 -19 -20 S Figure 8. UB NMR spectra of (CF3)3BCO (bottom), [ (CFj):; B C(O) OH ]~ (middle) and [(CFj^BCOip- (top). 34 —I-1--^-i-1—77—i-1-1-1-1-1-1— -1-■— 186.0 185 135 130 134.1 S Figure 10. 13C NMR spectrum of [(CF3)5BC(0)OH]- The expanded sections of the two signals show the 3J(13C.19F) coupling patterns. 35 36 tom) of [(CFa)aBCP]~ inCDjCN solution. 37 ^.7 39,6 39,5