IR/ EI MS Flashcards
Simple IR: C-H bond ranges
3100-3000 alkenes
3000-2850 alkanes
Simple IR: General carbonyl
1750-1600 ish range
Simple IR: Aldehyde
Two weak signals slightly below C-H; 2750 and 2850. && C=O 1750 peak.
Simple IR: Aromatic ring
Two peaks, around 1600 and 1475
Simple IR: Ketone
Around 1720
Simple IR: Amide
weak carbonyl signal due to conjugation with (N:) around 1690-1630
Simple IR: Ester
Check for a C-O bond around 1250 (low) and a high range C=O 1750ish.
IR: Hydrogen bonding: broad (concentrated or not?)
concentrated
IR: Hydrogen bonding: not broad (concentrated or not?)
diluted
IR: How to check for hydrogen bonding
If there isn’t hydrogen bonding, a high energy O-H stretch would occur around 3640-3610.
What does it mean when there is a m/z greater than the weight of the molecule?
There may be an isotope.
What is the correlation between MS intensity and stability?
A more stable molecule will have a higher intensity in MS.
Are double bonds a desired fragment?
Yes. The more conjugation, the more stable the fragment.
H Radical rearrangement
Hydrogen on a beta or gamma position can jump to the spot where there is a positive charge from missing electron. The other electron from the initial hydrogen bond stays on the original position.
McLafferty Rearrangement
Break the beta bond, gain the gamma hydrogen, and form a double bond to the alpha position
