Question

A simulated absorption spectrum of a gas-phase organic compound is shown in the following figure. Use the characteristic group frequencies listed in Table 8.4 (slide 15) to decide whether this compound is more likely to be ClhCO, (CH3) CO, CH3OH, CH COOH, CH:CN, CCli, or C3Hs. Explain your answer. [P8.26] 500 1000 500 2000 2500 3000 350 4000 Frequency/cm 1

Answer 1

Alkyl C-H stretch of C₃H₈ is present at around 3000 cm^-1

Also C-H Stretch around 3100 cm^-1 is very sharp and no other perks other than these two indicates the presence of C₃H₈

Rest of the possibility neglected due to following reasons

1. Cl₂CO absence of C=O stretch around 1700-1800 cm^-1
2. (CH₃)₂CO absence of C=O stretch around 1680-1750 cm^-1
3. CH₃COOH absence of C=O stretch around 1710-1800 cm^-1
4. CH₃CN absence of C≡N stretch around 2220-2260 cm^-1
5. CCl₄ absence of C-Cl stretch around 850-550 cm^-1
6. C₃H₈ absence of C≡N stretch around 2220-2260 cm^-1
7. CH₃OH absence of O-H stretch broad peak around 3200-3300 cm^-1 and C-O stretch around 1100-1200 cm^-1