Lecture 21 quartet caused by methyne H being affected by 3 other H (align/oppose) all with 2 with, 1 against 2 against, 1 with ↑↑↑ ↑↑↑ ↑↑↑ ↑↑↑ → probable ↑↑↑ ↑↑↑ ↑↑↑ ↑↑↑ frequency 1:3:3:1 ratio; unequal intensity no observable coupling > 3 bonds proximity (connected by 3 or less bonds) does not occur if a H gets the same amount of interaction from all affecting Hs, total # interacting H + 1 = multiplicity N+1 rule: if a H gets the same amount of interaction from all affecting Hs, total # interacting H + 1 = multiplicity all # of Hs that couple to provide splitting pattern ex 3 + 1 = 4 (quartet, "q"), 1 + 1 = 2 (doublet, "d") coupling constant: separation btw peaks (J values) ↑ constant, ↑ interaction split distance (Hz) mutual interaction; coupling constant (J) same for methyne quartet and methane doublet peaks next to one another if same J 2 influencing H → 2+1 = 3 → triplet 4 influencing H → 4+1 = 5 → quintet singlet: no coupling, all chem. equivalent diff. H can couple to diff. extents. Ha (b+c) = Ha Hb (c) = Hb Hc (b) = Hc all groups inequiv. a 2x larger a has 2H and within 3 bonds of a, which can be 1 or 2 → triplet a split by b (2 bonds away) → doublet a split by c (3 bonds away) → doublet of doublets a split by b & c (2 & 3 bonds away) → doublet of doublets 3 * 2 = 12 peaks b split by a (2 bonds away) → doublet b split by c (2 bonds away) → doublet of doublets; not a triplet 2 * 2 = 4 peaks c split by a (3 bonds away) → doublet c split by b (2 bonds away) → doublet of doublets 2 * 2 = 4 peaks quartet doublet of doublets equal chance of 4 prob. 1:3:3:1 two diff. possibilities unlike a triplet (1 and 1 are same) amount of coupling depends on # of bonds away & angle m Jbc Jbd 15Hz 10Hz further away within 3 Jbc Jbd 2Hz 2Hz closer tgt. a is split by b b is split by a c is split by b d is split by c known ex. to evaluate Ho, 2 other H within 3 bonds, diff coupling constants w/each = doub of doub. any order → same pattern Jcd Jcd