General Organic Chemistry

Syllabus Unit: Organic Chemistry

Why it matters

Chapter overview

General Organic Chemistry (GOC) is the toolkit every later organic topic depends on: naming any compound systematically, tracking how electron density shifts through a molecule (inductive, mesomeric, hyperconjugative effects), predicting which reactive intermediate forms and how stable it is, and judging acid/base strength from conjugate species stability. NEET questions across hydrocarbons, haloalkanes, alcohols and carbonyl chemistry all lean on the reasoning built here.

Chemistry Syllabus Organic Chemistry ~50% weightage

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Identify the principal characteristic group (highest seniority)

Select the longest chain containing that group

Number the chain for lowest locants

List substituent prefixes alphabetically with locants

1IUPAC Nomenclature

IUPAC naming is a fixed algorithm — find the principal characteristic group, find the longest chain containing it, number for lowest locants, then list substituents alphabetically.

Learning Objectives

Identify the longest continuous carbon chain that contains the principal characteristic group.
Apply the lowest-locant rule when numbering the parent chain.
Rank functional group seniority for choosing the suffix (carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine).
Name a compound bearing multiple substituents, listing them alphabetically with correct locants.

Key Terms

Principal Characteristic GroupThe functional group of highest seniority present in a molecule; it is expressed as the suffix, all others are named as prefixes.

LocantThe number assigned to a carbon atom in the parent chain, used to specify the position of substituents or the principal characteristic group.

Substituent PrefixThe name given to any group other than the principal characteristic group, attached to the parent chain as a prefix (e.g. chloro-, methyl-, nitro-).

Parent ChainThe longest continuous carbon chain that includes the principal characteristic group; forms the base name of the compound.

IUPAC nomenclature follows a fixed procedure so that every organic compound has exactly one systematic name: identify the senior functional group, find the longest chain containing it, number for lowest locants, then attach substituent prefixes alphabetically.

Step 1: Choose the principal characteristic group

When more than one functional group is present, only the most senior one becomes the suffix; all others are named as prefixes. The standard seniority order (highest to lowest) is: carboxylic acids > esters > amides > nitriles > aldehydes > ketones > alcohols > amines > ethers.

Step 2–4: Chain, numbering, substituents

Select the longest continuous carbon chain that includes the principal characteristic group (not necessarily the longest chain in the whole molecule).
Number the chain from whichever end gives the lowest locant to the principal characteristic group first; if there is a tie, give the lowest locants to substituents as a set.
List substituent prefixes in alphabetical order (ignoring multiplying prefixes like di-, tri-) with their locants, e.g. 4-chloro-3-methylhexan-2-one.

Common MistakeCommon trap: the longest chain is not always the visually 'longest line' drawn on paper — it must also contain the principal characteristic group, even if a longer chain exists elsewhere in the molecule.

Example: CH3-CH(CH3)-CH2-CHO → 3-methylbutanal (aldehyde is senior, chain chosen to include it, numbered from the CHO end)