IR Spectroscopy Flashcards
What information can we get from IR spectroscopy?
Information about functional groups
What does the x axis of an IR spectrum give us information about?
The frequency of light absorbed (bond strength).
What does the y axis give us information about?
How much light is absorbed (the dipole of the functional group).
In what area of an IR spectrum will you see signals for H-C (sp3) bonds?
2850 - 3000 cm^-1
If you have stretches between 2850 and 3000 cm^-1, what functional group do you have?
H-C (sp3) bonds
In what area of an IR spectrum will you see signals for H-C (sp2) bonds?
3000 - 3100 cm^-1
If you have stretches between 3000 and 3100 cm^-1, what functional group do you have?
H-C (sp2) bonds
How does greater s character in a hybrid orbital affect a stretch in an IR spectrum?
Greater s character will result in a shorter, stronger bond and, therefore, a higher absorption.
If you have a sharp stretch at 3300 cm^-1, what functional group do you have?
H-C (sp)
In what area of an IR spectrum will you see signals for H-C (sp) bonds?
Sharp stretch at 3300 cm^-1
What functional group do you have if you have a strong, broad stretch from 3200 - 3600 cm^-1?
An alcohol
In what area of an IR spectrum will you see the stretch for an alcohol O-H bond?
3200-3600 cm^-1
In what area of an IR spectrum will you see the stretch for an carboxylic acid O-H bond?
2200 - 3600 cm^-1
In what areas of an IR spectrum will you see the stretches for a carboxylic acid functional group?
1) Broad stretch between 2200 and 3600 cm^-1
2) Sharp stretch between 1700 and 1750 cm^-1
In what area of an IR spectrum will you see the stretch for an carboxylic acid O-C double bond?
1700-1750 cm^-1
What functional group do you have if you have a single, moderate stretch between 3350 and 3500 cm^-1?
A secondary amine
What functional group do you have if you have two moderate stretches between 3350 and 3500 cm^-1?
A primary amine
What sort of signal will a primary amine produce?
Two moderate stretches between 3350 and 3500 cm^-1
What sort of signal will a secondary amine produce?
One moderate stretch between 3350 and 3500 cm^-1
What sort of signal will an aldehyde C-H bond produce?
2750-2850 cm^-1, but hard to see
How will an EDG adjacent to a carbonyl affect the carbonyl’s signal in IR spectroscopy? Why?
The carbonyl stretch will be observed at a lower frequency, because the EDG stabilizes the charge-separated resonance contributor, giving the group more single-bond character.
How will an EWG adjacent to a carbonyl affect the carbonyl’s signal in IR spectroscopy? Why?
The carbonyl stretch will be observed at a higher frequency, because the EWG destabilizes the charge-separated resonance contributor, giving the group less single-bond character.
Where will the stretch for a C-C triple bond be on an IR spectrum?
2100-2200 cm^-1
Where will the stretch for a C-N triple bond be on an IR specturm?
2200-2300 cm^-1
