Formulas, functional groups and the naming of organic compounds — practice questions

1. Principal Functional Group: The –COOH group is a carboxylic acid, so the suffix is '-oic acid'.
2. Longest Chain: The longest chain containing the –COOH group has 4 carbon atoms (but-). The carbon in the COOH group is always C1.
3. Numbering: The chain is numbered starting from the carboxylic acid carbon as C1. So, C1 is the COOH carbon, C2 is CH₂, C3 is CH(CH₃), and C4 is CH₃.
4. Substituents: There is a methyl group (–CH₃) on carbon 3.
5. Assemble Name: The substituent is '3-methyl'. The parent chain is 'butan-'. The suffix is '-oic acid'. Combining these gives 3-methylbutanoic acid.

1. Name analysis: 'pentan-' means a 5-carbon chain. '-2-ol' means an –OH group is on carbon 2. '3-methyl' means a –CH₃ group is on carbon 3.
2. Structure: The chain is C-C-C-C-C. Numbering from the right, the –OH is on C2 and the –CH₃ is on C3. The structural formula is CH₃CH₂CH(CH₃)CH(OH)CH₃.
3. Skeletal Formula: Draw a zig-zag line with 5 points (for 5 carbons). From the second carbon, draw a line for the –OH group. From the third carbon, draw a line for the –CH₃ group.

$\text{Skeletal Formula}$

(A zig-zag line of 4 strokes representing the 5-carbon chain. A vertical line upwards from the 3rd carbon point. A line with 'OH' at the end coming off the 2nd carbon point.) 4. Classification: The carbon atom bonded to the –OH group (C2) is itself bonded to two other carbon atoms (C1 and C3). Therefore, it is a secondary (2°) alcohol.