Apply IUPAC rules to name and represent the structural formula of organic compounds including alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, carboxylic acids, esters, and amines

What this dot point is asking

NESA wants you to take any organic structural formula in the HSC scope and produce the IUPAC name, and to take any IUPAC name and draw the structural formula. The compounds in scope are alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, carboxylic acids, esters and amines, with branches up to about C6. This is the foundation for every other Module 7 dot point.

The answer

The five-step IUPAC algorithm

1. Identify the principal functional group to set the suffix. Priority (high to low): carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene/alkyne > alkane. Only the highest-priority group becomes the suffix; others become prefixes.
2. Find the longest continuous carbon chain that contains the principal functional group. The carbon count sets the parent name root (meth, eth, prop, but, pent, hex, hept, oct, non, dec).
3. Number the chain so that the principal functional group gets the lowest possible locant. If the principal group is at a chain end (acid, ester, aldehyde), it is automatically C1. For unsaturation, give the first $C=C$ or $C \equiv C$ the lowest locant. For substituents only, use the lowest set of locants.
4. Identify substituents (branches and lower-priority groups), assign their locants, and list them alphabetically.
5. Assemble the name: locants of substituents, substituent names (alphabetised), parent root, locant of principal group, suffix.

Suffix and general formula for each series

Locant rules in detail

Alcohols, aldehydes, ketones, amines, alkenes, alkynes all take a locant before the suffix: butan-2-ol, pent-2-ene, hex-3-yne, butan-2-one, butan-2-amine. Aldehydes and carboxylic acids do not need a locant because they are always C1.

Lowest locant rule. When two numbering directions are possible, choose the one that gives the lowest locant to the principal group. If the principal group has the same locant in both directions, choose the direction that gives the lowest locants to the substituents, taken as a set (compare term by term).

Substituent prefixes. Halogens are $fluoro$, $chloro$, $bromo$, $iodo$. Alkyl groups are $methyl$, $ethyl$, $propyl$, etc. An $-OH$ becomes a $hydroxy-$ prefix only when not the principal group (e.g. in 2-hydroxypropanoic acid, where the acid outranks the alcohol). An $-NH_2$ becomes $amino-$ when downgraded.

Worked example: name a complex structure

Structure: $CH_3CH_2CH(CH_3)CH_2CH_2OH$.

1. Principal group: $-OH$ (alcohol), suffix $-ol$.
2. Longest chain containing $-OH$: 5 carbons (pent).
3. Number to give $-OH$ lowest locant: from the OH end, OH at C1.
4. Substituent: methyl at C3.
5. Assemble: 3-methylpentan-1-ol.

Worked example: draw from name

Name: 4-amino-2-methylpentanoic acid.

• Parent: pentanoic acid means a 5 carbon chain with $-COOH$ at C1.
• Methyl at C2, amino at C4.

The acid outranks the amine, so $-NH_2$ is a prefix.

Naming esters specifically

Esters are named alkyl alkanoate in two words.

• Alkyl part: comes from the alcohol, named as a substituent off the ester oxygen. Count the carbons attached to the single-bonded $O$.
• Alkanoate part: comes from the carboxylic acid, includes the $C=O$. Count those carbons.

For $CH_3COOCH_2CH_3$: $CH_3CO-$ has 2 carbons (ethanoate), $-OCH_2CH_3$ has 2 carbons (ethyl). Name: ethyl ethanoate.

For $CH_3CH_2CH_2COOCH_3$: 4 carbons on the acid side (butanoate), 1 carbon on the alcohol side (methyl). Name: methyl butanoate.

Naming amines

A primary amine $R-NH_2$ takes the suffix $-amine$ with a locant for the nitrogen-bearing carbon. Secondary and tertiary amines are named by the largest parent amine, with the other substituents named with the $N-$ locant prefix. Example: $CH_3 - N(CH_3) - CH_2CH_3$ is $N,N$-dimethylethanamine (parent is ethanamine, two methyls on nitrogen).

Examples in context

Example 1. Labelling industrial chemicals at Orica Botany. Orica's Botany facility ships hundreds of products labelled with IUPAC names rather than common names because the Safety Data Sheet schema demands an unambiguous identifier. A tank truck of 2-chloropropan-1-ol is labelled with the IUPAC name plus the structural diagram, and the locant 2 makes clear that the chlorine sits on the central carbon while the OH sits on carbon 1. A misread label that swapped the locants would produce 1-chloropropan-2-ol, a different compound with different toxicology. The HSC five-step naming algorithm matches the SDS regulator's expectations one-to-one and is used by Orica safety officers when reviewing labels.

Example 2. NSW HSC depth study naming task. A common Stage 6 written task gives students 10 structural diagrams and asks for IUPAC names. A diagram showing $CH_3CH_2CH(OH)CH(CH_3)CH_2CH_3$ has a 6-carbon parent chain numbered from the right (to give OH the lowest locant); the principal group is the OH (suffix -ol) at position 3, with a methyl substituent at position 4, giving 4-methylhexan-3-ol. A student who counts from the left mislocates both groups and loses 2 marks. NESA marking schemes specifically reward "lowest set of locants" reasoning. Industrial scientists at the Australian Synchrotron also use these rules to log NMR samples.

Try this

Q1. Apply IUPAC rules to name each structure: (a) $CH_3CH_2CH=CH_2$, (b) $CH_3CH(OH)CH_2CH_3$, (c) $HCOOCH_2CH_3$. [3 marks]

• Cue. (a) But-1-ene. (b) Butan-2-ol. (c) Ethyl methanoate.

Q2. Draw the structural formula and write the molecular formula for 3-methylpentan-2-ol. [3 marks]

• Cue. 5-carbon parent chain with OH at C2 and methyl at C3; $CH_3CH(OH)CH(CH_3)CH_2CH_3$; $C_6H_{14}O$.

Q3. Provide IUPAC names for: (a) the addition product of HBr with prop-1-ene (Markovnikov); (b) the ester from propanoic acid and butan-1-ol; (c) the primary amine derived from propan-1-ol by direct ammonia substitution. [2+2+2 marks]

• Cue. (a) 2-bromopropane. (b) Butyl propanoate. (c) Propan-1-amine.