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NSWChemistryQuick questions
Module 7: Organic Chemistry
Quick questions on IUPAC nomenclature for organic compounds explained: HSC Chemistry Module 7
11short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the five-step IUPAC algorithm?Show answer
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.
What is locant rules in detail?Show answer
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.
What is worked example?Show answer
Structure: $CH_3CH_2CH(CH_3)CH_2CH_2OH$.
What is naming esters specifically?Show answer
Esters are named alkyl alkanoate in two words.
What is naming amines?Show answer
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).
What is lowest locant rule?Show answer
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).
What is substituent prefixes?Show answer
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).
What is forgetting the lowest locant rule?Show answer
Always renumber from both ends and choose the direction that minimises the principal group locant first.
What is ester order confusion?Show answer
Alkyl (from alcohol) is named first, alkanoate (from acid) second. The alkanoate carbons include the carbonyl.
What is including the carbonyl carbon twice?Show answer
When counting carbons in an aldehyde or carboxylic acid, the $C$ in $-CHO$ or $-COOH$ is C1, not an additional carbon.
What is alphabetising with prefixes?Show answer
Use only the letter of the substituent name itself, ignoring multipliers (di, tri, tetra). So $ethyl$ comes before $dimethyl$ alphabetically (e by e).