Question: 1. what is the difference between the pairs of 1-propene/2-propene and 1-butene/2-butene?
Answer: Thus, the word "1-butene" indicates a chain of four carbons, with a double bond between carbons 1 and 2; the word "2-butene" indicates a chain of four carbons, with a double bond between carbons 2 and 3. ... This leaves each carbon free to bond to two hydrogen atoms.