Question

How can we understand the position of a double bond or triple bond from the name of the hydrocarbon?

Short answer

Question: Based on the IUPAC nomenclature system, determine the position of the double bond in 3-hexene. Answer: In 3-hexene, the prefix "hex" indicates a six-carbon chain, and the suffix "ene" shows the presence of a double bond. The number 3 in the name specifies that the double bond starts from the third carbon atom. Therefore, the position of the double bond in 3-hexene is at the third carbon atom.

Step-by-step solution

Identify the prefix

The prefix of the name tells us the number of carbon atoms in the hydrocarbon. Common prefixes include: - Meth (1 carbon) - Eth (2 carbons) - Prop (3 carbons) - But (4 carbons) - Pent (5 carbons) - Hex (6 carbons) - Hept (7 carbons) - Oct (8 carbons) - Non (9 carbons) - Dec (10 carbons) To understand the position of double or triple bonds, first, look at the prefix of the hydrocarbon name to know the number of carbons in the molecule.

Identify the numbering for the position of the bond

The number in the name indicates the position of the double or triple bond. It is placed before the suffix of the name. For example, in 2-butene, the number 2 indicates that the double bond starts from the second carbon atom. The numbering starts from the end of the carbon chain nearest to the double or triple bond.

Identify the suffix

The suffix of the name tells us the type of bond present, a double bond or a triple bond. Suffixes for hydrocarbons containing double bonds are '-ene' and for triple bonds are '-yne'. For example: - Ethene (double bond) - Propyne (triple bond)

Putting it all together

Combine the prefix, bond position, and suffix to understand the position of a double or triple bond from the name of the hydrocarbon. For example: - 2-butene: a four-carbon chain (But) with a double bond (ene) starting from the second carbon atom (2). - 1-pentyne: a five-carbon chain (Pent) with a triple bond (yne) starting from the first carbon atom (1).