(II) A student isolated a natural product and after elucidating the structure using chemical and spectroscopic methods, he faced a problem in establishing the stereocenter at carbon-3. There were two possible isomers: A or B as shown below. Use the provided 'H-NMR and NOE spectra to help the student to find the correct structure. Circle the correct isomer and explain why you select this isomer. (5 Marks) CH2 H-3 CH2 CH 3- b 3 CH3-6 37 H-3 CH3-a CH3-a NOE (Irradiating CH3-a) CH3-a CH3-b Original 'H-NMR H-3 30 15 ppe Explain