Final answer:
The designation of an alkene as E, Z, or neither depends on the groups attached to the carbon atoms of the double bond and their spatial arrangement. Without different substituents allowing for distinction, the alkene would be considered neither E nor Z. Classification as an alkyne, alkene, or alkane is based on the type of carbon-to-carbon bonds present in the molecule.
Step-by-step explanation:
To determine if an alkene is E, Z, or neither, we must evaluate the groups attached to the carbon atoms of the double bond. If a molecule has a C=C bond with different groups attached, it may exist as geometric isomers. These isomers are named according to their spatial arrangement—E for entgegen (opposite sides) and Z for zusammen (same side). For a simple alkene like 2-butene, you could have cis-2-butene (Z) with both methyl groups on the same side of the double bond, or trans-2-butene (E) with the methyl groups on opposite sides of the double bond.
However, if an alkene does not have groups on the carbon atoms of the double bond that allows for cis or trans (or E/Z) distinction, then it would be considered neither. Examples of this would be when the double bond is between two quaternary carbons or when the substituents are identical so that flipping does not change the molecule. In such cases, there are no geometric isomers.
The molecule's characteristics—such as the presence of a triple bond, a single double bond, or only single bonds—determine whether it is an alkyne, alkene, or alkane respectively.