Topic 21: Spectroscopic Identification of Organic Compounds

Vocabulary based flashcards covering analytical techniques, mass spectrometry, IHD, IR spectroscopy, and NMR spectroscopy as detailed in the Topic 21 lecture notes.

Qualitative analysis

The detection of the presence but not the quantity of a substance in a mixture.

Quantitative analysis

The measurement of the quantity of a particular substance in a mixture.

Structural analysis

A description of how the atoms are arranged in molecular structures.

Mass spectrometry (MS)

A technique used to determine relative atomic and molecular masses and identify molecules based on their fragmentation.

• Shoots electrons

  • can knock off electron of atom [Mg (g) + e^- → Mg⁺ (g) + 2e^-]

  • can break apart molecule

• C-H and C=O do not fragment

Degree of Unsaturation (Index of Hydrogen Deficiency, IHD)

A calculation used to determine the number of double bonds or rings for a given molecular formula: $IHD = (0.5)(2c + 2 - h - x + n)$.

Degree of Unsaturation (Standard values)

A double bond counts as one degree of unsaturation, a triple bond as two, a ring as one, and an aromatic ring (benzene) as four.

Infrared (IR) spectroscopy

A technique using relatively low energy to cause bonds in molecules to vibrate, providing information on functional groups.

Wavenumber

The reciprocal of wavelength ($1/\lambda$) typically used to cite IR absorptions.

UV-vis spectroscopy

A technique that gives information about the electron energy levels in an atom.

Chemical shift ($\delta$)

The position of an NMR signal relative to the standard tetramethylsilane (TMS) signal, measured in $\text{ppm}$.

Integrated trace

The area under the curve in a $^{1}H$ NMR spectrum which reveals the relative number of protons in a particular hydrogen environment.

High-resolution $^{1}H$ NMR spectroscopy

A form of NMR that reveals previously-thought single peaks as groups of distinct, smaller peaks due to spin-spin coupling.

Spin-spin coupling

The splitting of NMR peaks that occurs when hydrogens on adjacent carbon atoms interact with one another.

$(n + 1)$ Rule

A formula used to determine splitting where $n$ refers to the number of hydrogen atoms on adjacent carbon atoms.

Singlet

A single NMR peak indicating the hydrogen environment is adjacent to a carbon with no hydrogen atoms.

Doublet

A cluster of 2 peaks indicating the hydrogen environment is adjacent to a carbon with 1 hydrogen atom.

Triplet

A cluster of 3 peaks indicating the hydrogen environment is adjacent to a carbon with 2 hydrogen atoms.

Quartet

A cluster of 4 peaks indicating the hydrogen environment is adjacent to a carbon with 3 hydrogen atoms.