Final answer:
Cycloheptatriene is not aromatic because it does not comply with Hückel's rule for aromaticity, which requires a planar structure and a count of 4n+2 π electrons; cycloheptatriene has 6 π electrons and is not planar.
Step-by-step explanation:
The reason cycloheptatriene cannot be considered aromatic is because it does not fulfill the criteria required for aromaticity according to Hückel's rule. A molecule must have a cyclic ring with conjugated double bonds, resulting in a delocalized pi electron system that contains a total of 4n+2 π electrons (where n is a non-negative integer) to be considered aromatic. Cycloheptatriene has seven carbon atoms and three double bonds, which means it has 6 π electrons (not fitting the 4n+2 formula where n would have to be 1.5, which is not a non-negative integer). Additionally, for a molecule to exhibit aromaticity, it needs to be planar to allow for the overlap of p orbitals. Since cycloheptatriene cannot achieve this planarity and does not have the correct number of π electrons, it lacks the characteristic electron delocalization and, thus, cannot be aromatic.