Spectroscopy and Lab Techniques

IR spectroscopy frequencies and appearance

H NMR spectroscopy

• each chemically non-equivalent molecule generates a distinct signal

• protons attached to the same carbon are equivalent and the same distance from a certain common group

• chemical shift: protons with less electron density around is considered deshieleded and will appear downfield (left) on the NMR spectrum (next to an electronegative element)

• multiplicity: indicates the number of non-equivalent immediately neighboring protons by n+1

• integration: numbers above an NMR signal that indicate the relative number of protons giving rise to each signal

C NMR spectroscopy

• chemically non-equivalent carbons in a molecule generate a distint signal

• more deshielded carbons will be located downfield to the left

• why is it important?: determining if a carbonyl-containing functional group is present in a molecule

degrees of unsaturation

DOU= (2C+2+N-X-H)/2

mass spectroscopy

molecular fragments are send through a long tube and deflected

• molecular ion peak: tallest peak in the rightmost section and represent’s the compound’s molecular mass

• base peak: tallest peak in the entire spectrum and corresponds to the most stable molecular fragment

UV-Vis spectroscopy

• used to analyze molecules with conjugated pi bonds

• a higher maximum absorptoon means the molecule has more conjugated pi bonds

extraction

• separate a mixture based on differing solubility properties

• polarity: use water (polar) and a organic solvent (nonpolar) to separate layers

• acidity: use a base (acidic) and an organic solvent (neutral)

thin layer chromatography

the more polar a compound, the slower it will travel UP

• retention factor (R_f): distance the comppund traveled divided by the distance a solvent traveled — inversely proportional to the polarity of a compound

column chromatography

• separates components in a mixture

• the more polar the compound, the more it will interact with the silica in the column and the slower it will travel

gas-liquid chromatography

• used to determine the relative abundance of comppunds

• a compound with a higher boiling porint travles slower and thus has a longer retention time

distillation

• separate a mixture of two miscible liquids

• simple: when volatile liquids have differing boiling points

• fractional: when liquid have similar boiling points

• the lower boiling point liquid of the mixture is collected in the receiving flask because it boils first (simple)

• the lower boiling point liquid comprises a larger portion of the vapor in the fractional column (fractional )

recrystallization

• used for purifying solids