What is the IUPAC name for CH3-CH(CH3)-CH2-CH3?

The correct IUPAC name for CH3-CH(CH3)-CH2-CH3 is indeed 2-Methylbutane. To determine this name, we start by identifying the longest continuous carbon chain in the molecule, which consists of four carbons (the base name “butane”).

Next, we observe that there is a methyl group (CH3) attached to the second carbon of this butane chain. In the nomenclature system, substituents must be indicated by their position on the main chain, which is numbered to give the lowest possible numbers to the substituents. Since the methyl group is on the second carbon, we denote this as "2-methyl".

Therefore, combining what we have identified, we arrive at the name 2-Methylbutane, which accurately reflects both the structure and the substituents present in the compound. Other names presented do not fit the structural characteristics of the compound. For instance, 1-Butene would imply an alkene with a double bond at the first position, while 3-Methylpentane suggests a five-carbon chain with a methyl group at the third carbon, both of which do not correspond to the given structure. Butylenes refers to a