structures, IUPAC nomenclature and properties of the main organic families (alkanes, alkenes, haloalkanes, alcohols, aldehydes, ketones, carboxylic acids, esters, amines and amides) and the recognition of structural isomers (chain, position and functional-group isomers)

What this dot point is asking

VCAA wants you to draw and name members of the main organic families using IUPAC rules, to classify alcohols and amines as primary, secondary or tertiary, and to recognise structural isomers (chain, position and functional-group isomers) including drawing their structural formulas.

The answer

The main families

The functional group is the reactive part of the molecule. The rest of the molecule (the carbon skeleton) is named separately.

IUPAC naming procedure (alkane skeleton, then go up)

1. Identify the longest carbon chain that contains the principal functional group. This is the parent chain.
2. Number the chain so the principal functional group gets the lowest locant. (For multiple groups, follow the priority order: COOH > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne > halide.)
3. Identify the substituents (alkyl groups, halogens, etc.) attached to the chain and their locants.
4. Combine in the form (substituents with locants alphabetical)-(parent chain)-(suffix).
5. Use commas between numbers; hyphens between numbers and letters; no spaces.

Bracketed locants are mandatory when ambiguous. "Propan-2-ol" not "propanol" if the OH could be on C1 or C2 (well, propan-1-ol if on C1).

Primary, secondary, tertiary alcohols and amines

For an alcohol: count the number of carbon atoms bonded to the C bearing the OH.

• Primary (1 deg): OH carbon bonded to 1 other C (e.g. ethanol).
• Secondary (2 deg): OH carbon bonded to 2 other C (e.g. propan-2-ol).
• Tertiary (3 deg): OH carbon bonded to 3 other C (e.g. 2-methylpropan-2-ol).

Important because only primary alcohols oxidise to aldehydes (and on to carboxylic acids), secondary alcohols oxidise to ketones (and no further), and tertiary alcohols do not oxidise under normal conditions.

For an amine: count carbons attached to the N.

• Primary: N bonded to 1 carbon (e.g. ethanamine, CH3CH2NH2).
• Secondary: N bonded to 2 carbons (e.g. N-methylmethanamine, CH3NHCH3).
• Tertiary: N bonded to 3 carbons (e.g. trimethylamine, (CH3)3N).

Structural isomers

Same molecular formula, different connectivity. Three types appear in VCE:

1. Chain isomers (skeletal): same functional group, different carbon skeleton.
   Butane (CH3CH2CH2CH3) and 2-methylpropane ((CH3)3CH) are chain isomers of C4H10.

2. Position isomers: same skeleton and same functional group, different position of the group on the chain.
   Propan-1-ol (CH3CH2CH2OH) and propan-2-ol (CH3CH(OH)CH3) are position isomers of C3H8O.

3. Functional-group isomers: same molecular formula, different functional group.
   Ethanol (CH3CH2OH) and methoxymethane (CH3OCH3, dimethyl ether) are functional-group isomers of C2H6O.

Naming esters

An ester is named in two parts: alkyl (from the alcohol) followed by alkanoate (from the carboxylic acid).

For CH3CH2COOCH3:

• The R-O- side (from methanol) gives the alkyl part: methyl.
• The R-COO- side (from propanoic acid) gives the alkanoate part: propanoate.
• Name: methyl propanoate.

Reverse the procedure to build the structure from the name. For ethyl ethanoate: ethanoic acid contributes -COO-CH2CH3 minus the OH; ethanol contributes the -OCH2CH3 part. Structure: CH3COOCH2CH3.

Worked example

Name CH3CH(OH)CH2CH(CH3)2.

Step 1. Longest chain containing the OH: 4 carbons (the methyl branch is not on the main chain unless we make it so). Let us check: there is a branched isopentane structure here. The longest chain containing the OH is C4: HO-CH-CH2-CH-CH3 with a methyl on the inner CH. Let me re-write: CH3-CH(OH)-CH2-CH(CH3)2. Counting from the OH end: C1 (CH3), C2 (CHOH), C3 (CH2), C4 (CH bearing the (CH3)2). C5 from the C4 substituent.

Wait, the iso-group means C4 has two methyl substituents. Strictly the longest chain is 5 carbons: take one of the two methyls of the iso-group as part of the main chain. Chain: CH3-CH(OH)-CH2-CH(CH3)-CH3 with the OTHER methyl off C4 as a substituent. That's 5 carbons total.

Step 2. Number from the end nearest the OH: C1 to C5 with OH on C2 and CH3 on C4.

Step 3. Name: 4-methylpentan-2-ol.

Step 4. Classification: OH carbon (C2) bonded to one CH3 (C1) and one CH2 (C3). Two carbons attached. Secondary alcohol.

Common traps

Numbering from the wrong end. Always number so the principal functional group (alcohol, COOH, etc.) gets the lowest locant. Halogens and alkyl groups do not take priority over the functional group.

Forgetting locants on small molecules. Propan-2-ol, not propanol (the latter is ambiguous, although in practice means propan-1-ol).

Mis-counting carbons in esters. Methyl ethanoate has TWO carbons in the acid part and ONE in the alcohol part, despite looking like an ester of methanol. The methyl is from the alcohol, the ethano- is from the acid.

Calling tert-butanol a primary alcohol. Count the carbons on the OH-bearing carbon. (CH3)3COH has 3 carbons on that C, so it is tertiary.

Confusing position and chain isomers. Same skeleton + different group position = position isomer. Different skeleton entirely = chain isomer.

Drawing an amide as if it were an amine. An amide has a C=O next to the N (R-C(O)-NHR'); an amine does not.

In one sentence

IUPAC names build from the longest carbon chain containing the principal functional group with locants chosen so that group gets the lowest number, primary/secondary/tertiary refers to the number of carbons on the functional-group-bearing carbon, and isomers can differ in skeleton (chain), in the position of the same group (position), or in the functional group entirely (functional-group isomers).