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UB CHE 202 MS

Mass Spec Heavier Isotope Peaks, Important Definitions and numbers

QuestionAnswer
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)
Created by: HugsAndKisses