Ressonância Magnética Nuclear

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204 Chapter 10 USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY TO DEDUCE STRUCTURE lines-a "triplet of triplets"-by the combined coupling with two neighboring cis hydrogens and two neighboring trans hydrogens ([2 + 1 = 3] X [2 + = 3] = 9). Conversely, the signal for the CH₂ groups at δ = 2.4 may be split into four lines-a "doublet of doublets"-by different size coupling with the cis and trans hydrogens on the neighboring CH₂ group ([1 + = 2] X + 1 = 2] = 4). (i) The signal for the CH₃ group at δ = 1.2 will be split into a triplet by the neighboring CH₂ group. In the simplest possible situation, the signal for the CH₂ group at δ = 2.0 will be split into a quintet by the combined effect of its neighboring CH₃ group and the CH group on its other side (on the carbonyl carbon). The signal for the CH group at δ = 9.5 will be split into a triplet O by its neighboring CH₂ group. As we shall see in Chapter 17, coupling constants to the H-C- hydrogen are smaller than usual and lead to more complicated patterns with more lines than the simple N + 1 rule predicts. In reality, the signal for the CH₂ group will be split into a quartet of doublets. (j) The signals at δ = 0.9 and δ will be singlets (no neighbors). The signal for the CH₃ group at δ = 1.4 will be split into a doublet by the neighboring CH group. The signal for the CH group at δ =4.0 will be split into a quartet by the neighboring CH₃ group. 45. Procedures are similar to those of Problem 44. We show each structure below, and near each group of hydrogens, the multiplicity of its signal (in plain English, the number of lines into which it is split), by using one of the following abbreviations: s, singlet; d, doublet; t, triplet; q, quartet; quin, quintet; sex, sextet; sept, septet; oct, octet; and non, nonet. All multiplicities have been determined by applying + 1 rule. CH₃ (s) CH₃ (d) (quin) (a) CH₃CCH₂CH₃, BrCH₂CHCH₂CH₃, CH₃CHCH₂CH₂Br (q) (t) (d) (oct) (t) (non) (q) (t) Br (d) CH₂Cl (quin) CH₃ (s) (t) / (t) (s) (d) (d) (s) (b) ClCH₂CH₂CH₂CH₂OH, CH₃CHCH₂OH, (oct) (s) (s) CI (s) (d) (d) (s) (s) (s) CH₃ CH₃ CH₃ CH₃ CH₃ CH₃ (s) (q) (d) (d) (t) (c) CICH₂C CHCH₃, CCH₃, CHCH₃, CICH₂CHCCH₃ (s) (sept) (d) (sex) Br Br CH₃ Br Br CH₃ 46. In some cases assignments of signals with similar chemical shifts cannot be unambiguously made without further information, such as integration data. (a) δ = 5.8 4.0 ppm 6 5 4 3 2 ppm (δ)