Draw and number the structure:
CH₃ — CH₂ — CH(OH) — CH₂ — CH₃
C1 C2 C3 C4 C5
Longest chain = 5 carbons → parent: pentane
Locate and number the functional group:
—OH is on C3 (numbered from either end — C3 from both sides in this symmetric molecule)
Functional group suffix: -ol
Construct IUPAC name:
Parent: pent (5 carbons) + ane (no double bond) + -ol (alcohol)
Position: 3
IUPAC name: Pentan-3-ol ✓
Step 1: Find the longest continuous carbon chain containing the principal functional group — this is the parent chain. Step 2: Number the chain from the end nearest the principal functional group (or, if no functional group, from end giving substituents the lowest locants). Step 3: Name substituents as prefixes (alphabetically) with their position numbers. Step 4: Add the functional group suffix. Step 5: Apply appropriate prefixes for double/triple bonds (-ene/-yne) with their positions.
📌 Highest priority (suffix): –COOH (carboxylic acid, -oic acid)
📌 –CHO (aldehyde, -al)
📌 –CO– (ketone, -one)
📌 –OH (alcohol, -ol)
📌 –NH₂ (amine, -amine)
📌 Double bond C=C (-ene) and triple bond C≡C (-yne) also get locants
📌 Lowest priority (prefix only): halogen (halo-), nitro- (–NO₂), alkoxy- (–OR)
Parent chain includes the carbon bearing –OH. Number from end nearest –OH. Suffix: -ol. Examples: CH₃OH = methanol, CH₃CH₂OH = ethanol, CH₃CH(OH)CH₃ = propan-2-ol (NOT 2-propanol in modern IUPAC). When –OH is at C1: pentan-1-ol. At C2: pentan-2-ol. At C3 of pentane: pentan-3-ol (as in this question).
Aldehydes (–CHO): parent chain must include the CHO carbon. Suffix: -al. The CHO carbon is always C1 (no need to specify position). Examples: HCHO = methanal (formaldehyde), CH₃CHO = ethanal (acetaldehyde), CH₃CH₂CHO = propanal. Ketones (–CO–): parent chain includes both carbons of C=O. Suffix: -one. Position must be specified for chains ≥5 carbons. CH₃COCH₃ = propan-2-one (acetone), CH₃COC₂H₅ = butan-2-one.
In IUPAC system, ethers are named as alkoxy alkanes. The longer chain is the parent alkane; the shorter chain + oxygen is the alkoxy group. CH₃OCH₃ = methoxymethane, CH₃OC₂H₅ = methoxyethane, C₂H₅OC₂H₅ = ethoxyethane (diethyl ether). Common names (methyl ether, ethyl ether etc.) are still used in practice but not in strict IUPAC.
📌 –COOH: -oic acid. HCOOH = methanoic acid, CH₃COOH = ethanoic acid
📌 Acid chloride –COCl: -oyl chloride. CH₃COCl = ethanoyl chloride
📌 Anhydride –CO–O–CO–: -oic anhydride. (CH₃CO)₂O = ethanoic anhydride
📌 Ester –COOR: alkyl -oate. CH₃COOC₂H₅ = ethyl ethanoate
📌 Amide –CONH₂: -amide. CH₃CONH₂ = ethanamide
📌 Nitrile –CN: -nitrile or -carbonitrile. CH₃CN = ethanenitrile
Primary amines (–NH₂): parent chain + -amine. CH₃NH₂ = methanamine, C₂H₅NH₂ = ethanamine. Secondary amines (R–NH–R'): smaller group named as N-substituent. CH₃NHCH₃ = N-methylmethanamine. Tertiary amines: both extra groups named as N-substituents. Common names: methyl amine, dimethylamine, trimethylamine are widely used for first few members.
Cyclic alkanes: cyclo- prefix + parent name. Cyclopropane (C₃), cyclobutane (C₄), cyclopentane (C₅), cyclohexane (C₆). Benzene derivatives: if functional group is on ring, ring is the parent (benzene, cyclohexane). CH₃C₆H₅ = methylbenzene (toluene). Substituents on benzene are named with ortho (1,2), meta (1,3), para (1,4) positions or with locant numbers.