Spectroscopic Analysis of Acyl Chlorides

• IR  - presence of high frequency C=O, C-Cl too low to be useful

Absorbance (cm-1)	Interpretation
1800	C=O stretch

• ¹H NMR - only the protons adjacent to the C=O are particularly characteristic.

 

Resonance (ppm)	Interpretation
~2 - 2.5	H-C-C=O


 
• ¹³C NMR

C=O typically 160-180 ppm (deshielding due to O)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

two absorption maxima p®p^* (<200 nm) n®p^* (~235 nm)
• p electron from p of C=O
• n electron from O lone pair
• p^* antibonding C=O

• Mass Spectrometry

Prominent peak corresponds to formation of acyl cations (acylium ions)

Spectroscopic Analysis of Anhydrides

• IR  - presence of two, high frequency C=O

 

Absorbance (cm-1)	Interpretation
1820	C=O stretch
1750	C=O stretch

• ¹H NMR - only the protons adjacent to the C=O are particularly characteristic.

 

Resonance (ppm)	Interpretation
~2 - 2.5	H-CC=O


 
• ¹³C NMR

C=O typically 160-180 ppm (deshielding due to O)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

two absorption maxima p®p^* (<200 nm) n®p^* (~225nm, diagnostic)
• p electron from p of C=O
• n electron from O lone pair
• p^* antibonding C=O

• Mass Spectrometry

Prominent peak corresponds to formation of acyl cations (acylium ions)

Spectroscopic Analysis of Esters

• IR  - presence of C=O, and two C-O bands (Csp²-O and Csp³-O bonds)

 

Absorbance (cm-1)	Interpretation
1735	C=O stretch
1300-1000	two bands for C-O stretch

• ¹H NMR - deshielded proton of H-C-O is often recognizable, and H-C-C=O.

 

Resonance (ppm)	Interpretation
3.5-4.5	H-COC
2-2.5	H-C-C=O


 
• ¹³C NMR

C=O typically 160-180 ppm (deshielding due to O)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

two absorption maxima p®p^* (<200 nm) n®p^* (~207 nm)
• p electron from p of C=O
• n electron from O lone pair
• p^* antibonding C=O

• Mass Spectrometry

Prominent peak corresponds to formation of acyl cations (acylium ions)

Spectroscopic Analysis of Amides

• IR  - presence of low frequency C=O, N-H stretches for 1^o or 2^o amides.

 

Absorbance (cm-1)	Interpretation
1660	C=O stretch
3500 and 3100	N-H stretch (two for NH2, one for NH)

• ¹H NMR - N-H protons often broad,

 

Resonance (ppm)	Interpretation
5-8  (broad, exchangeable)	NH
~ 2 - 2.4	H-C-C=O


 
• ¹³C NMR

C=O typically 160-180 ppm (deshielding due to O)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

absorption maxima n®p^* (~215 nm)
• n electron from O lone pair
• p^* antibonding C=O

• Mass Spectrometry

Molecular ion M+ often visible.
A prominent peak corresponds to formation of acyl cations (acylium ions)


 

Spectroscopic Analysis of Nitriles

• IR  - very characteristic CºN stretch (only CºC is similar region)

Absorbance (cm-1)	Interpretation
2250	CºN stretch

• ¹H NMR - only protons adjacent to CºN are likely to be characteristic.

Resonance (ppm)	Interpretation
2 - 3	H-C-CºN


 
• ¹³C NMR

CºN typically 115 -125 ppm (deshielding due to N)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

Simple nitriles usually show no absorption above 200 nm.
 
 
• Mass Spectrometry

Molecular ion M+ is often weak or absent, but a weak M-1 peak due to loss of an a-H is often present.