Question | Answer |
hydrocarbon | small M+1 peak |
Br present | M+ = M+2 |
Cl present | M+2 is 1/3 of M+ |
I present | Peak at 127, large gap |
Odd amount of N present | Odd M+ |
S present | M+2 will be 4% of M+ |
Alcohol | M+ may not be visible because loss of a water molecule is so stable |
Only ______ are detected by Mass Spec | cations |
Which is more important? The Stability of the radical or the Cation | Stability of the cation |
molecular ion | the ion obtained by the loss of one electron from the molecule (M+) |
Base peak | the most intense peak |
Radical cation | positively charged species with an odd number of electrons |
fragment ions | lighter cations (and radical cations) formed by the decomposition of the molecular ion. Usually correspond to stable cations |
m/z | mass to charge ratio. Usually charge is +1 so it seems to be graphed based on mass |
difference from M+ with loss of a methyl group | 15 |
difference from M+ with loss of a ethyl group | 29 |
difference from M+ with loss of a water | 18 |
difference from M+ with loss of CO | 28 |
difference from M+ with loss of CO2 | 44 |
difference from M+ with loss of ethene | 28 |
Common cleavage for alkanes | to give most stable carbocation |
common cleavage for alcohols | 1) lose a water, or 2) alpha cleavage - break between the C bearing the OH and a neighboring carbon. Resonance stabilization allows O to bear some of the + charge |
Common cleavage for alkenes and aromatics | to give allylic and benzylic carbocations. Cleave one away from the ring or double bond so the positive charge ends up next to the ring/double bond NOT on it |
Common Cleavage of amines | alpha cleavage between C attached to N and neighboring C. N helps to stabilize by bearing the + charge by forming a double bond with the C |
Commone cleavage of ethers | loss of an alkyl group. 1) cleave between C-O 2) alpha cleavage leaving C-O bonds intact |
Common cleavage of ketones and aldehydes | loss of alkyl groups next to the carbon bearing the oxygen to give acylium ions (C triple bond to O) |