Spectroscopy Problems I

Eight structure elucidation problems based on 1H nmr, 13C nmr and some infrared spectroscopic data are presented below. In each case, from the nineteen formulas shown at the bottom of the page (A through S), select that one which best fits the evidence. Enter the appropriate letter in the answer box to the right of the question. Do not enter punctuation (eg. commas or semicolons) or spaces.

1. A C5H12O2 compound has strong infrared absorption at 3300 to 3400 cm-1 The 1H NMR spectrum has three singlets at δ 0.9 , δ 3.45 and δ3.2 ppm; relative areas 3:2:1. The 13C NMR spectrum shows three signals all at higher field than δ100 ppm. Suggest a structure for this compound.   2. A C4H8O2 compound has a strong infrared absorption at 1150 cm-1, but no absorption at 3300 to 3400 cm-1. It's 1H NMR spectrum shows a singlet at δ 3.55 ppm. The 13C NMR spectrum shows one signal at δ 66.5 ppm. Suggest a structure for this compound.
3. A C9H12O compound has strong infrared absorption at 3300 to 3400 cm-1. The 13C NMR spectrum of this compound has six discrete signals. It's 1H NMR spectrum has three sets of lines: singlets at δ1.1 (6H), 1.9 (1H) and 7.3 (5H) ppm. Suggest a structure for this compound. 4. A C10H14 compound. The 1H NMR spectrum has two singlets at δ 2.45 and 7.0 ppm (ratio = 6:1). The 13C NMR spectrum shows three signals at δ132.9, 130.5 and 18.9 ppm. Suggest a structure for this compound.
5. A C8H4N2 compound shows a sharp infrared absorption at 2230 cm-1. It's 1H NMR spectrum has a singlet at δ 7.6 ppm. The 13C NMR spectrum shows three signals at δ132, 119 and 117 ppm. Suggest a structure for this compound. 6. A C14H22 compound. The 1 H NMR spectrum has two singlets at δ 1.1 and 7.25 ppm (ratio = 9:2). The 13C NMR spectrum shows four signals at δ 147, 125, 39.3 and 30.8 ppm. Suggest a structure for this compound.
7. A C9H12O3 compound has strong infrared absorption near 1100 cm-1. Its 1H NMR spectrum has sharp singlet peaks at δ 3.6 and 6.6 ppm (intensity ratio 3:1). Its 13C NMR spectrum shows three lines at δ 165, 115 and 55 ppm. Suggest a structure for this compound. 8. A C9H18O compound has a strong infrared absorption at 1710 cm-1. Its 1H NMR spectrum has a single sharp peak (a singlet) at δ 1.2 ppm. Its 13C NMR spectrum shows three lines at δ210, 45 and 25 ppm. Suggest a structure for this compound.

     
This script written by William Reusch, Dept. of Chemistry, Michigan State University. Please send comments and corrections to whreusch@pilot.msu.edu.