CHE 118A - Spectroscopy

FTIR spectroscopy

solution or thin film

attenuated total reflectance (ATR) FTIR

pure solid or liquid sample

for solution samples

remember to exclude solvent bands from interpretation

NB

H2O absorbs strongly in IR so cannot be used as a solvent

nujol

heavy liquid paraffin used to make mull

saturated

Cn H2n+2

no pi bonds, no rings

1 degree unsaturation

Cn H2n

1 pi bond (1 double bond)

2 degree unsaturation

Cn H2n-2

2 pi bonds (2 double bonds/triple)

3 degree unsaturation

2 pi bonds plus a ring

calculate hydrogen deficiency index (HDI)

½ (2C + 2 + N - H - X)

UV-visible absorbance spectroscopy

isaac newton determined that visible white light was split into components with different wavelengths using a prism

extinction coefficient

is for a specific wavelength and if this is a max on the spectrum, it’s called lamda max

the longer the wavelength,

the more conjugated the aromatic system (no max above 250 NM = no conjugation/aromaticity)