PHAR 307 - Lecture 13: mass spectrum interpretation

molecular ion peak

ion formed after undergoing ionization and not fragmenting, usually last peak but sometimes missing

molecular adducts

ions formed when molecule interacts with other species such as solvent molecules, counterions, small ions

isotopic peaks

molecular ion peaks with smaller mass unit peaks due to presence of different isotopic masses of element

energy needed to remove electron from highest to lowest

sigma bonds, non conj pi bonds, conj pi bonds, non bonding or lone pair

order of stability highest to lowest

aromatic, alicyclic, n-hydrocarbons, ketone, branched chain hydrocarbon, alcohols

daughter ions are often

cations and radicals

fragmentation of alkanes

occurs adjacent to most substituted carbon atom

fragmentation of alkenes

allylic carbocations favored

fragmentation of aromatics

benzene and phenyl = most stable species = will not fragment further, if possible species will form tropylium ion

tropylium ion formation

alpha cleavage

formation of double bond due to fragmentation (electron from ionized atom + one from sigma bond)

loss of water

M-18

what is the product (loss of water)

+H2O

alpha cleavage of alkyl radical cleaves

preferentially largest group

preferentially fragments into

less preferably fragments into

anilines commonly fragment off

HCN

aniline fragmentation

McLafferty rearrangment

transfer of hydrogen from one part of molecular ion to another

McLafferty rearrangement conditions

appropriately located heteroatom (non H or C), double bond, extractable hydrogen atom which is gamma to C=O system

McLafferty rearrangement process