Question

Draw the condensed structural formula for alkenes and alkynes or the line-angle structural formula for cycloalkenes for each of the following:

Part A

1,2-dibromocyclopentene

Draw the molecule on the canvas by choosing buttons from the Tools (for bonds), Atoms, and Advanced Template toolbars.

Part B

2-hexyne

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Part C

cis-2-heptene

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Answer 1

Part A) The IUPAC's norms for naming organic compounds gives that the root of the name be the longest unbroken carbon chain, with substituents being prefixes. In case of multiple substituents, those that form a part of the carbon chain like carbonyls and unsaturations become the suffixes. Thus, it can be inferred that the primary skeleton of the given molecule is a five-carbon ring i.e. cyclopentane, with one double bond. From the substitutent numbers 1 and 2, it can be inferred that the two bromine atoms are in the carbon atoms involved in the unsaturation since those get the first priority. Thus, the given molecule's structure is as follows.

Part B) Following IUPAC's norms, it can be inferred that the given molecule's skeleton is a six-carbon chain with 1 C-C triple bond between the second and third carbons of the chain, which gives it the following structure.

Part C) From the root hept, it can be noted that the skeleton is a seven-carbon chain and the suffix gives that the molecule has 1 C-C double bond between the second and third carbons in the chain. Now, the prefix cis gives that the bulky substituents across the double bond are on the same side. Thus, the molecule has the following structure.