(CH$_3$)$_2$CHCH(OH)CH$_2$C(CH$_3$)$_3$ The IUPAC name of the compound above is

Analyze the question: We need the IUPAC name of (CH₃)₂CH–CH(OH)–CH₂–C(CH₃)₃.

Concept: To name an alcohol:

1. Find the longest carbon chain that contains the carbon bearing the –OH.
2. Number from the end that gives the –OH carbon the lowest possible number.
3. Name and locate the substituents, then write them in the order: substituents, parent, then -ol with its position.

Solution:

Expand the structure:

(CH₃)₂CH – CH(OH) – CH₂ – C(CH₃)₃

• (CH₃)₂CH– is a carbon with two methyl groups.
• CH(OH) is the carbinol carbon.
• CH₂ is a methylene carbon.
• C(CH₃)₃ is a quaternary carbon with three methyls.

Longest chain: CH₃–CH–CH(OH)–CH₂–C–CH₃ gives 6 carbons, so the parent is hexane.

Numbering from the left (the CH₃ on the isopropyl end):

• C1: CH₃
• C2: CH (with a methyl branch)
• C3: CH(OH)
• C4: CH₂
• C5: C (with two methyl branches)
• C6: CH₃

Numbering from the right would put the –OH at C4, so the left-hand numbering is correct, giving –OH at C3.

Substituents: a methyl at C2 and two methyls at C5, so 2,5,5-trimethyl.

Name: 2,5,5-trimethylhexan-3-ol

Why the others are wrong:

• B and C use non-systematic or incorrectly built names.
• D numbers the chain so that –OH is at position 4, which breaks the lowest-number rule for the functional group.

Tip: In naming alcohols, the –OH gets the lowest number first, before any substituents. Then count the methyl branches carefully and use "tri" for three methyls (here 2, 5, 5).