Name and draw the structural and displayed formulae of unbranched: (a) alkanes (b) alkenes, including but-1-ene and but-2-ene (c) alcohols, including propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol (d) carboxylic acids containing up to four carbo

Naming Organic Compounds – Unbranched Alkanes, Alkenes, Alcohols & Carboxylic Acids

1. Unbranched Alkanes

Alkanes are simple chains of carbon atoms bonded only with single bonds. Think of them as a string of beads where each bead is a carbon atom.

  1. Count the number of carbon atoms → that gives the prefix (meth-, eth-, prop-, but-, etc.).

  2. Add the suffix ‑ane to form the name.

CnH2n+2NameStructural Formula
CH4Methane\$\\mathrm{CH_4}\$
C2H6Ethane\$\\mathrm{CH3CH3}\$
C3H8Propane\$\\mathrm{CH3CH2CH_3}\$
C4H10Butane\$\\mathrm{CH3CH2CH2CH3}\$

Exam Tip: Remember the general formula for alkanes: \$\\mathrm{CnH{2n+2}}\$. If you can write the formula, you can quickly check the name.

2. Unbranched Alkenes

Alkenes contain at least one carbon–carbon double bond. The suffix changes to ‑ene and we number the chain to give the double bond the lowest possible number.

  1. Count carbons → prefix.

  2. Number chain from the end nearest the double bond.

  3. Write the double bond position before the suffix.

CnH2nNameStructural Formula
C2H4Ethene\$\\mathrm{CH2=CH2}\$
C3H6Propene\$\\mathrm{CH2=CHCH3}\$
C4H8But-1-ene\$\\mathrm{CH2=CHCH2CH_3}\$
C4H8But-2-ene\$\\mathrm{CH3CH=CHCH3}\$

Exam Tip: For alkenes, the double bond takes priority in numbering. If two double bonds exist, number to give the first double bond the lowest number.

3. Unbranched Alcohols

Alcohols contain a hydroxyl group (‑OH). The suffix becomes ‑ol and the position of the OH group is indicated.

  1. Count carbons → prefix.

  2. Number chain from the end nearest the OH group.

  3. Write the OH position before the suffix.

CnH2n+1OHNameStructural Formula
C3H8OPropan-1-ol\$\\mathrm{CH3CH2CH_2OH}\$
C3H8OPropan-2-ol\$\\mathrm{CH3CH(OH)CH3}\$
C4H10OButan-1-ol\$\\mathrm{CH3CH2CH2CH2OH}\$
C4H10OButan-2-ol\$\\mathrm{CH3CH(OH)CH2CH_3}\$

Exam Tip: The OH group is the “anchor” for numbering. If the chain is symmetrical, choose the numbering that gives the lowest possible OH position.

4. Carboxylic Acids (≤4 Carbons)

Carboxylic acids contain a carboxyl group (‑COOH). The suffix becomes ‑oic acid and the chain is numbered from the end nearest the carboxyl group.

  1. Count carbons → prefix.

  2. Number chain from the end nearest the COOH group.

  3. Replace the suffix ‑ane with ‑oic acid.

CnH2n-2O2NameStructural Formula
C2H4O2Acetic acid\$\\mathrm{CH_3COOH}\$
C3H6O2Propionic acid\$\\mathrm{CH3CH2COOH}\$
C4H8O2Butyric acid\$\\mathrm{CH3CH2CH_2COOH}\$

Exam Tip: The carboxyl group (‑COOH) is the “anchor” for numbering. If the chain is symmetrical, choose the numbering that gives the lowest possible COOH position.

5. Quick Reference Cheat‑Sheet

PrefixSuffixExample (C4)
But-‑aneButane – \$\\mathrm{CH3CH2CH2CH3}\$
But-‑ene (1‑ or 2‑)But‑1‑ene – \$\\mathrm{CH2=CHCH2CH_3}\$
But-‑ol (1‑ or 2‑)But‑2‑ol – \$\\mathrm{CH3CH(OH)CH2CH_3}\$
But-‑oic acidButyric acid – \$\\mathrm{CH3CH2CH_2COOH}\$

Exam Tip: When in doubt, write down the carbon chain first, then add the functional group and suffix. This systematic approach reduces mistakes.