Final answer:
To classify alkenes in vitamin A by their carbon substituents, we follow the IUPAC naming convention, where the longest chain with the double bond gets the base name with -ene, and the lowest numbered carbon in the double bond indicates its position. Geometric isomers demonstrate different spatial arrangements of atoms despite having the same bonding order, due to the rigidity of the double bond.
Step-by-step explanation:
To classify each alkene in vitamin A by the number of carbon substituents bonded to the double bond, we first need to understand the basic rules for naming alkenes as per the International Union of Pure and Applied Chemistry (IUPAC). An alkene is named after the longest carbon chain containing the double bond with the suffix -ene. The position of the double bond is indicated by the lowest numbered carbon participating in the bond.
For example, in a 4-carbon alkene named butene, there can be 1-butene and 2-butene, based on where the double bond is located. 1-butene has the double bond starting with the first carbon, while 2-butene has it starting with the second carbon. This positioning becomes important when looking at geometric isomers, such as cis-2-butene and trans-2-butene, which have the same bonding order but differ in the arrangement of atoms in space due to the lack of rotation about the double bond.
In naming an alkene, even if substituents are present, the double bond takes priority in the numbering of the carbon chain, which is done to ensure the double bond carbon atoms receive the lowest possible numbers. For instance, a molecule named 5-methyl-2-hexene has a methyl group on the fifth carbon and a double bond between carbon two and three.