Measurement and Data Processing - Spectroscopic identification of organic compounds

The Index of Hydrogen Deficiency ($IHD$) provides the number of rings and/or $\pi$ bonds in a molecule. For a compound with the general formula $C_c H_h N_n O_o X_x$, the $IHD$ is calculated to determine degrees of unsaturation.

Mass Spectrometry ($MS$) is used to determine the relative atomic and molecular masses. The molecular ion peak ($M^+$) gives the molar mass of the compound, while fragmentation patterns (e.g., $m/z = 15$ for $CH_3^+$ or $m/z = 29$ for $C_2H_5^+$) help deduce the structure.

Infrared ($IR$) Spectroscopy identifies functional groups based on the absorption of infrared radiation, which causes specific bonds to vibrate. Key absorptions include $O-H$ (broad peak at $3200-3600 \text{ cm}^{-1}$) and $C=O$ (strong peak at $1700-1750 \text{ cm}^{-1}$).

Proton Nuclear Magnetic Resonance ($^1H$ NMR) provides information on the chemical environment of hydrogen atoms. The chemical shift ($\delta$) is measured in parts per million ($ppm$) relative to the standard Tetramethylsilane ($TMS$), which is assigned $\delta = 0$.

In high-resolution $^1H$ NMR, the splitting pattern of a signal (multiplicity) follows the $n+1$ rule, where $n$ is the number of protons on adjacent carbon atoms.

The fingerprint region in an $IR$ spectrum is the area below $1500 \text{ cm}^{-1}$ which is unique to every compound and is used for specific identification by comparison with a database.