a. According to the IR and NMR spectra, what types of C-H bonds are present in t

Question

a. According to the IR and NMR spectra, what types of C-H bonds are present in the molecule?

b. Are there other diagnostic features of the IR spectrum?

c. What information about the carbon skeleton does the NMR provide?

d. Propose a structure for the compound, try to assign the most abundant peak in the mass spectrum:

An explanation would be helpful.

Problem #3 1755 1820 IR Spectrum (liquid film) 800 1600 1200 2000 3000 4000 v (cm Mass Spectrum 100 55 60 8 M+ 158 (k 1%) 40 C8H1403 40 80 120 160 200 240 280 m/e 1H NMR Spectrum (200 MHz, CDCl3 solution) expansion 2.00 1.50 ppm

Explanation / Answer

The presence of sp3 C-H is revealed by the absorptions in the 2850-2990 cm-1 region, [2850-3000 cm-1 sp3 C-H, 3000-3100 cm-1 sp2 C-H, 3300 cm-1 sp C-H]. Two absorption peaks at 1755, 1820 indicates CO stretching vibrations of saturated anhydride. NMR spectrum gives the half of the integration of the protons which implies the symmetric nature of molecule. A sextet with integration of 2 suggests the presence of-CH2 group in between –CH2 and –CH3 (ie, -CH2-CH2-CH3) The structure of the molecule is CH3-CH2-CH2-CO-O-CO-CH2-CH2-CH3. The most abundant peak (m/z = 71) is due to CH3-CH2-CH2-CO+

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