The document discusses the McLafferty rearrangement, which is a reaction observed using mass spectrometry. The rearrangement involves a carbonyl compound undergoing cleavage of alpha and gamma bonds, resulting in an enol radical cation and a neutral alkene fragment. Fred McLafferty first observed this reaction using mass spectrometry. The reaction proceeds through a six-membered ring transition state and has specific requirements for the carbonyl compound. Examples of compounds undergoing the rearrangement include 2-hexanone and hexanoic acid.

1. McLafferty Rearrangement
GUNASEELAN R
21CHE15

2. What is McLafferty Rearrangement?
 Mass spectroscopy is a technique used to determine the mass of a given molecule.
 The molecule is placed inside the spectrometer and ionized by high-energy electrons.
 After the molecules are ionized, they become radical cations that can then be sorted and weighed.
 When hydrogen is available at the gamma position on carbonyl compounds, these compounds go through a
specific rearrangement due to the cleavage of multiple bonds, including the bonds at alpha and gamma positions.
 This reaction is known as the McLafferty rearrangement.
 Fred Warren McLafferty was an American chemist known for his work in mass spectrometry.
 He is best known for the McLafferty rearrangement reaction that was observed with mass
spectrometry.

3.  The rearrangement involves a six-membered ring transition state in which the carbonyl group pulls off
the gamma proton, splitting the molecule into two pieces.
 These pieces consist of an enol radical cation and a neutral alkene fragment.
 𝝅 𝐞𝐥𝐞𝐜𝐭𝐫𝐨𝐧𝐬
 n electrons
 𝜸 𝐩𝐫𝐨𝐭𝐨𝐧𝐬
Requirements for McLafferty Rearrangement
Carbonyl compound Ethene Enol radical cation

4. MECHANISM OF McLAFFERTY REARRANGEMENT
STEP 𝟏
STEP 𝟐
Carbonyl compound
Enol radical cation tautomers
NOTE
Y can be H,R,OH,OR or NR2

5. STEP 𝟑
Ethene
Fragmented ion
Examples
2-Hexanone Propene
Acetone enol
radical cation
Hexanoic acid 1-Butene
Acetic acid enol
radical cation
APPLICATION
 An application of this rearrangement
is in structural elucidation using mass
spectroscopy as the tool.