Question

(1) Determine the Degree of unsaturation (2) Completely assign all relevant peaks in the IR spectrum (3) Completely assign all peaks in the 13C NMR spectrum (4) Completely assign all peaks in the 1H NMR spectrum (5) Provide the structures (not the molecular formulas) of the ions: 102 and 120 in the mass spectrum (6) Provide the correct structure for this molecule.

Answer 1

Degree of unsaturation

Degree of unsaturation = (2C + N - H - X+ 2)/2

C is the number of carbons,   N is the number of nitrogens

X is the number of halogens (F, Cl, Br, I) and H is the number of hydrogens

Degree of unsaturation = (2x9 + 2 - 10 +2) / 2 = 6

Hence the compound has 6 degree of unsaturation

IR spectrum

There are sp3 and sp2 C-H stretching presents around ~ 2950 cm-1 and 3050cm-1.

The Peak at 2200 is responsible for CN group

13C NMR

There are 4 peaks at aromatic region (110- 160). The peak at ~95 ppm may responsible for CN group. Apart from only one methyl carbon is present  in aliphatic region

1H NMR

1H NMR shows two doublets from 6-8 ppm that belongs to aromatic proton and the pattern confirms that the ring is substituted at 1,4 position. The singlet at 3.0 ppm belongs to methyl group.

using all the information, we can deduce the structure

CN 4-(dimethylamino)benzonitrile Chemical Formula: CgH10N2 Molecular Weight: 146.19 ChemNMR 'H Estimation 3.02 3.02 PPM ChemNMR 13C Estimation 152.5 111.7 S111.7 133.1 133.1 102.1 il 118.6 za 160 140 120 100 80 6040200 PPM

Mass spectrum CN Exact Mass: 146.08 Exact Mass: 120.08 CN Exact Mass: 102.03