Slats18 said:3-pentene would actually be 2-pentene, and it would look something like this (excluding H's)
C-C=C-C-C or C-C-C=C-C
I see what you were trying to get at, but when you say 3-pentene, you're saying there is a 5 carbon chain that is the longest (correct) AND that there is a double bond connecting the 3rd and 4th carbon atoms =)
The IUPAC name for this organic molecule is the International Union of Pure and Applied Chemistry name, which is a systematic way of naming organic compounds based on their molecular structure.
The IUPAC name is determined by identifying the longest carbon chain in the molecule and numbering the carbons in that chain. Functional groups and substituents are then added to the name in alphabetical order, with their corresponding carbon numbers noted.
The purpose of using IUPAC names is to have a standardized and universal system for naming organic compounds. This makes it easier for scientists to communicate and share information about different molecules, as well as to avoid confusion and errors in chemical reactions and experiments.
There are some exceptions and variations in the IUPAC naming system, particularly for complex molecules or those with multiple functional groups or substituents. In these cases, prefixes and suffixes may be used to indicate the specific location and arrangement of these groups.
While common or trivial names may be easier to remember and use, they are not as precise and specific as IUPAC names. It is always recommended to use the IUPAC name when communicating about organic molecules in a scientific context.