Question

Tarragon oil is a mixture of many constituent oils. Treatment of Oil 1 with N-Bromosuccinimide and light yields Oil 2. When Oil 2 is reacted with magnesium in ether followed by carbon dioxide and acid workup, Oil 3 is formed. Spectral data for Oil 3 are given below. Mass spec: m/z = 194. IR: 3330-2500 (broad with peaks at 3080, 3060, 2970, 2960), 1696 om-1 1H NMR: 11.6 (singlet, 1H), 7.2 (doublet, 2H), 7.0 (doublet, 2H), 3.7 (singlet, 3H), 2.9 (triplet, 1H), 1.9 (quintet, 2H), 1.6 (triplet, 3H). Which of the following is the structure of Oil 3? A B C D

Answer 1

NB S, light Allylic bromination Mg, ether Grignard formatio Mg Br 1. CO2 2. H H20 Grignard reacts with CO2 to give carboxylicacid OH 116 7.2 29 1.6 7.0 3.7 7.0 11.6 (singlet, 1H) -protron of carboxylic acid OH group. So, structure A or B 7.2 (doublet, 2H) - Aromatic protron 7.0 (doublet, 2H) - Aromatic protron 3.7 (singlet, 3H) 2.9 (triplet, 1H) 1.9 (quintet, 2H) 1.6 (triplet, 3H) So, structure B No, 1 protron in structure A

Answer is B.