Molecular Formula: C8H8O

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Molecular formula: C8H8O
Molecular formula: C8H8O

The unknown organic sample had a molecular formula of C8H8O. Due to some element of symmetry, the 13C NMR showed only 6 signals. The 13C NMR spectrum shows 5 downfield signals between 128 to 193ppm. With the downfield signals and the 5 Degrees of Unsaturation it is suggested that the molecule is a monosubstituted aromatic compound. Ha

Ha

Hb
Hb
Hb
Hb

Hc
Hc
Hc
Hc

Hd
Hd

Figure 1. Four proton signals- a, b, c, d- in unknown molecule
The number of signals in the 1HNMR spectrum indicates the number of nonequivalent protons in a molecule. Chemically equivalent protons give the same signal in the NMR whereas nonequivalent protons give different signals. Therefore, the compounds C8H8O have four signals in their 1H NMR spectra: one at 7.94 ppm (the two equivalent CH’s), one at 7.56ppm (the two equivalent CH’s), one at 7.64 ppm (the CH) and the other at 2.50 ppm (the CH3) (Fig. 2). The relative intensities of the signals indicate the numbers of protons that are responsible for individual signals. The area under each peak is measured in the form of an integral line. The unknown organic molecule has one singlet, one doublet; two triplets that have integration areas whose ratio is 3:2:2:1 respectively. This indicates that there are one methyl group and five CH groups (Fig. 2).

Figure 2. ChemDraw Simulated NMRs

Figure 2. ChemDraw Simulated NMRs

ChemDraw Simulated 1H NMR spectrum

ChemDraw Simulated 1H NMR spectrum

ChemDraw Simulated 13C NMR spectrum
ChemDraw Simulated 13C NMR spectrum

The locations of the peaks (chemical shift, ppm) indicate the types of protons in the molecule. This results from the fact that the magnetic field at the nucleus varies with the electronic (structural) environment for each type of proton. The CH3 protons of the unknown molecule are shielded and appear upfield at 2.5 ppm. The CH’s protons are deshielded due to the electrons in the π bonds circulate...
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