1 What makes an acid “carboxylic”? 📖

A carboxylic acid contains the functional group –COOH, a carbonyl (C=O) linked to a hydroxyl (–OH) — that’s why it’s called the carboxyl group. These acids can be aliphatic (RCOOH) or aromatic (ArCOOH) depending on whether an alkyl (R-) or aryl (Ar-) group is attached to the carboxyl carbon. Many occur in nature; long-chain members (C12–C18) form the fatty-acid part of natural fats. They’re key starting materials for esters, anhydrides, acid chlorides, amides, and more. :contentReference[oaicite:0]{index=0}

2 Naming made easy 📝

2.1 Common names (everyday chemistry) 😎

  • End with -ic acid.
  • Often honor the natural source: formic acid (formica = ant), acetic acid (acetum = vinegar), butyric acid (butyrum = butter). :contentReference[oaicite:1]{index=1}

2.2 IUPAC rules (exam-ready) 🎯

  1. Start with the parent alkane name.
  2. Replace the ending -e with -oic acid.
    Example: CH3COOH → ethane → ethanoic acid.
  3. Number the chain so the carboxyl carbon is 1.
  4. More than one -COOH? Add prefixes: dicarboxylic acid, tricarboxylic acid, etc., and show their positions (e.g., benzene-1,2-dicarboxylic acid). :contentReference[oaicite:2]{index=2}

2.3 Quick name bank 🔍

StructureCommon nameIUPAC name
HCOOHFormic acidMethanoic acid
CH3COOHAcetic acidEthanoic acid
CH3CH2COOHPropionic acidPropanoic acid
CH3CH2CH2COOHButyric acidButanoic acid
(CH3)2CHCOOHIsobutyric acid2-Methylpropanoic acid
HOOC-COOHOxalic acidEthanedioic acid
HOOC-CH2-COOHMalonic acidPropanedioic acid
HOOC-(CH2)2-COOHSuccinic acidButanedioic acid
HOOC-(CH2)3-COOHGlutaric acidPentanedioic acid
HOOC-(CH2)4-COOHAdipic acidHexanedioic acid
HOOC-CH2-CH(COOH)-CH2-COOHTricarballylic acidPropane-1,2,3-tricarboxylic acid
(aromatic) COOHBenzoic acidBenzenecarboxylic acid
Ph-CH2COOHPhenylacetic acid2-Phenylethanoic acid
benzene-(1,2)-(COOH)2Phthalic acidBenzene-1,2-dicarboxylic acid

(All names from Table 8.3) :contentReference[oaicite:3]{index=3}

3 Geometry & resonance 🧑‍🔬

The three bonds around the carboxyl carbon lie flat in one plane, separated by about 120°. Because the lone pair on oxygen can delocalize, the group shows resonance:

\[ \ce{R–C(=O)–OH <=> R–C^{δ+}(=O)–O^{δ-}} \]

This resonance makes the carboxyl carbon less electrophilic than an ordinary carbonyl carbon. :contentReference[oaicite:4]{index=4}

4 High-yield NEET takeaways 🚀

  1. Naming trick: swap the parent-alkane -e for -oic acid; carboxyl carbon is always number 1.
  2. Resonance effect: delocalization lowers electrophilicity — useful when predicting reactivity trends.
  3. Planar geometry (≈ 120°): handy for stereochemical questions and reaction-mechanism reasoning.
  4. Classification: spot the difference between aliphatic RCOOH and aromatic ArCOOH acids quickly.
  5. Common vs IUPAC names: formic ↔ methanoic, acetic ↔ ethanoic, etc.—a favorite for simple one-mark conversions.

5 Let’s recap in one line 💡

Know how to name, recognize the planar resonating carboxyl group, and you’ll ace almost every carboxylic-acid question that shows up! 🎉