Spectroscopy Problems II

Eight structure elucidation problems based on 1H nmr, 13C nmr and 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 C9H10O compound has a strong infrared absorption at 1720 cm-1. Its 1H NMR spectrum has signals at δ 2.8 (mult., 4H), 7.3 (s, 5H) and 9.8 (t, 1H) ppm. Its 13C NMR spectrum shows seven lines at δ200, 138, 129, 128, 125, 35 and 30 ppm. Suggest a structure for this compound.   2. A C5H10O2 compound shows a strong infrared absorption at 1100 cm-1, but no absorption at 3300 to 3400 cm-1. Its 1H NMR spectrum has sharp singlet peaks at δ1.3 and 4.0ppm (intensity ratio 3:2). Its 13C NMR spectrum shows three lines at δ 98, 68 and 20 ppm. Suggest a structure for this compound.
3. A C9H10O2 compound has strong infrared absorption at 1690 and 1100 cm-1 . Its 1H NMR spectrum has sharp singlet peaks at δ 2.8 and 3.8 ppm (3H each) and two doublets at δ 6.9 and 7.8 ppm (2H each). Its 13C NMR spectrum shows seven lines Suggest a structure for this compound. 4. A C9H10O2 compound has strong infrared absorption at 1695 cm-1. The 1H NMR spectrum has five sets of lines: a triplet at δ1.3(3H), a quartet at δ>4.1(2H), a doublet at δ7.0(2H), a doublet at δ7.8(2H) and a singlet at δ9.8(1H) ppm. Suggest a structure for this compound.
5. A C4H8O3 compound has strong infrared absorption at 2500 to 3300 cm-1 and 1710 cm-1 . The 1H NMR spectrum has four signals: a doublet at δ1.2(3H), a quartet at δ4.5(1H), a singlet at δ3.6(3H) and a singlet at 12.5 ppm. The 13C NMR spectrum has four signals at δ177, 70, 54 and18 ppm. Suggest a structure for this compound. 6. A C9H9N compound shows infrared absorption at 2250 cm-1. It's 1H NMR spectrum has three signals: sharp singlets at δ 2.4 (3H), 3.8 (2H) and a broader one at 7.2 (4H) ppm. The 13C NMR spectrum has seven signals, five at fields lower than δ100 ppm and two at higher fields. Suggest a structure for this compound.
7. A C4H11N compound shows two infrared absorption bands at 3200 to 3400 cm-1 and a strong band at 2900 cm-1. It's 1H NMR spectrum shows two singlets at δ 1.0 (9H) and 1.3 (2H) ppm. The 13C NMR spectrum has two signals, both at fields higher than δ100 ppm. Suggest a structure for this compound. 8. A C5H11N compound shows infrared absorption at 3300 cm-1. It's 1H NMR spectrum has three signals: singlets at δ1.0 (6H), 1.4 (1H) and 2.7 (4H) ppm. The 13C NMR spectrum has three signals, all at fields higher than δ100 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.