Understanding the Concept:
The McLafferty rearrangement is a well-established intramolecular fragmentation pathway that occurs during mass spectrometry for radical cations containing an unsaturated functional group (such as ketones, aldehydes, esters, or alkenes).
Step 1: Evaluate Statement A and D
The McLafferty process is a unimolecular fragmentation reaction driven by electron ionization. It begins with a radical cation precursor and undergoes a cyclic redistribution of bonds, breaking an axial carbon-carbon bond to yield two distinct fragments: an enol radical cation species (which is detected) and a complementary neutral alkene fragment molecule. Thus, Statements A and D describe true aspects of the mechanism.
Step 2: Evaluate Statement B
The spatial arrangement required for this rearrangement involves a sterically favorable six-membered cyclic transition state. The radical site on the unsaturated heteroatom reaches across to abstract a hydrogen atom from the carbon at the gamma (\(\gamma\)) position relative to the carbonyl group:
\[
\text{[C}_\gamma\text{-H]} \cdots \text{[O=C}_\alpha\text{]}^{+\bullet}
\]
Because it proceeds through this specific geometry, Statement B is true.
Step 3: Evaluate Statement C
Statement C claims the reaction occurs in *any* compound that has a hydrogen atom on the \(\gamma\)-carbon. This statement is overly broad and incorrect. For a McLafferty rearrangement to take place, the molecule must also contain an unsaturated, polarizable double-bond group (such as a carbonyl \(\text{C=O}\), an imine \(\text{C=N}\), or an alkene \(\text{C=C}\)) to accept the migrating proton. A pure saturated alkane containing a \(\gamma\)-carbon lacks this functional group requirement and cannot undergo this rearrangement. Since Statement C is false, it is the correct answer to this question.