The^19F,^79Br. and^8lBr nuclei are NMR active. The presence of these nuclei in a

Question

The^19F,^79Br. and^8lBr nuclei are NMR active. The presence of these nuclei in a molecule can result in additional coupling in the^1H-NMR spectrum. The^79Br and^81Br nuclei each have a spin quantum number I = 3/2, but both have large quadrupole moments which make their nuclei almost undetectable in a normal^1H-NMR experiment. In contrast, the^119F nucleus has a spin quantum number I = 1/2 (same as^1H and^l3C nuclei) and is 100% abundant. These properties make^19F-NMR data easy to obtain, and allow^l9F-^1H and^19F-^13C coupling to be observed in^1H- and^l3C-NMR spectra. This "extra" coupling can be a powerful diagnostic tool for structural determination of^l9F containing molecules. Use the J_HF coupling constants shown below to predict the^1H-NMR coupling pattern of each possible substituted benzoic acid product obtained from the Grignard reaction. For reference J_CF coupling constants can be found on the course website

Explanation / Answer

Doublet for equivalent proton Ha and Ha' due to Hb and Hb' further coupled with F with J=8.9Hz

Doublet for equivalent proton Hb and Hb' due to Ha and Ha' further coupled with F with J=5.7Hz

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