Análise de Espectroscopia de RMN

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split into a quartet, so it must be coupled to a CH₃ group. This CH₃ group must be split into a triplet by the CH₂ group. Where is the signal for this CH₃ group? Careful examination of the signal at 1.2 δ reveals that it is actually two triplets. One of these triplets must be the signal for that CH₃ group. The quartet at 2.3 δ is due to hydrogens of another CH₂ group. From its chemical shift, this is probably the CH₂ which is bonded to the carbonyl carbon of the ester group. Because this CH₂ appears as a quartet, it is also attached to a CH₃ group. This CH₃ group is responsible for the other triplet near 1.2 The compound is an ester with two ethyl groups, one bonded to the oxygen of the ester and one to the carbonyl carbon of the ester. It is ethyl propanoate. 14.24 The DU is 2. The very broad OH absorption and the carbonyl peak at 1706 cm⁻¹ in the IR spectrum show that the unknown is a carboxylic acid. The absence of alkene and aromatic bands (no C=C) suggest the presence of a ring (C=O and ring give DU = 2). The singlet at 11.7 δ in the spectrum is consistent with the hydrogen of a carboxylic acid. The other signals in this spectrum are too complex to be much help. The presence of only four different types of carbons in the spectrum indicates some symmetry in the structure. The C at 182 δ is due to the carbonyl carbon of the carboxylic acid. O To sum to the total of six C's and ten H's, there must be C two of both kinds of CH₂ groups. Assembly of these OH fragments gives cyclopentanecarboxylic acid. 14.25 The DU is one. The carbonyl band at 1741 cm⁻¹ and the C-O absorption near 1250 cm⁻¹ indicate that the unknown is an ester. This accounts for the DU. The most downfield signal in the spectrum, at 4.2 δ, must be from a CH₂ (integral =2) attached to the oxygen of the ester group. It is a triplet, so this CH₂ is bonded to another CH₂. The singlet at 2.1 δ (integral =3) results from a CH₃ group with no nearby H's. Its chemical shift is consistent with a methyl group that is attached to the carbonyl group of the ester. The signal at 1.6 δ appears to contain five lines. This indicates a CH₂ group (integral =2) bonded to two CH₂ groups (at 4.2 and 1.4 with similar coupling constants. The signal at 1.4 δ appears to contain six lines. This indicates a CH₂ group (integral =2) bonded to a CH₂ group (at 1.6 and a CH₃ group (at 0.9 δ) with similar coupling constants. Thus, the unknown is an ester with a butyl group on the oxygen and a methyl group on the carbonyl carbon. The most 222