Meditaliano IMAT Prep
Lesson 15: The Ultimate Guide to Chemical Nomenclature
Introduction: The Grammar of Chemistry
Nomenclature is the systematic grammar of chemistry. For the IMAT, rote memorization of simple salts is insufficient. You must master the IUPAC rules to deduce structures from complex names (and vice versa), understand stereochemical indicators, and recall common "trivial" names that persist in medical literature. This lesson has been expanded to cover advanced inorganic ions, detailed organic priority rules, and a massive reference library for your study.
Expanded Learning Objectives
- LO 15.1: Inorganic Nomenclature: Polyatomic ions, variable charge metals, coordination complexes, and hydrated salts.
- LO 15.2: Acid Nomenclature: Distinguishing binary acids, oxyacids, and their corresponding salts.
- LO 15.3: Advanced Organic Rules: Tie-breaking numbering, complex substituents, cyclic compounds, and functional group priority.
- LO 15.4: Stereochemistry: R/S configurations, E/Z isomerism, and Isomerism hierarchy.
- LO 15.5: Reference Library: Memorizing common names (Toluene, Aniline, Aspirin, etc.) and medical applications.
Part 1: Inorganic Ions & Salts
The foundation of inorganic nomenclature lies in the ions. You must memorize charges to construct neutral formulas. Below is a color-coded guide.
1.1 Extensive List of Polyatomic Ions
Beyond the basics, the IMAT may test knowledge of sulfur and phosphorus derivatives, as well as oxidizing agents.
| Charge | Name | Formula | Notes / Memory Aid |
|---|---|---|---|
| +1 | Ammonium | $NH_4^+$ | Bio Essential for amino acid synthesis. |
| +1 | Hydronium | $H_3O^+$ | Acid The actual form of protons in water. |
| +1 | Mercury(I) | $Hg_2^{2+}$ | Trap Diatomic cation! It's a dimer. |
| -1 | Hydroxide | $OH^-$ | Base Base identifier. |
| -1 | Nitrate | $NO_3^-$ | Soluble. Strong oxidizer. |
| -1 | Nitrite | $NO_2^-$ | Unstable, used in preservatives. |
| -1 | Acetate | $CH_3COO^-$ | Also written $C_2H_3O_2^-$. Organic. |
| -1 | Cyanide | $CN^-$ | Toxic Inhibits Cytochrome C Oxidase. |
| -1 | Permanganate | $MnO_4^-$ | Deep purple. Strong oxidizer ($Mn$ is +7). |
| -1 | Perchlorate | $ClO_4^-$ | $Cl$ is +7. Explosive potential. |
| -1 | Chlorate | $ClO_3^-$ | $Cl$ is +5. |
| -1 | Chlorite | $ClO_2^-$ | $Cl$ is +3. |
| -1 | Hypochlorite | $ClO^-$ | Bleach active ingredient ($Cl$ is +1). |
| -1 | Bicarbonate | $HCO_3^-$ | Bio Crucial blood buffer. |
| -1 | Bisulfate | $HSO_4^-$ | Hydrogen sulfate. Acidic salt component. |
| -1 | Thiocyanate | $SCN^-$ | Sulfur analog of cyanate. |
| -2 | Carbonate | $CO_3^{2-}$ | Limestone, marble. Insoluble (except Group 1). |
| -2 | Sulfate | $SO_4^{2-}$ | Stable sulfur form. |
| -2 | Sulfite | $SO_3^{2-}$ | Reducing agent ($SO_2$ source). |
| -2 | Thiosulfate | $S_2O_3^{2-}$ | Used in iodometric titrations. |
| -2 | Chromate | $CrO_4^{2-}$ | Yellow. $Cr$ is +6. Toxic. |
| -2 | Dichromate | $Cr_2O_7^{2-}$ | Orange. $Cr$ is +6. Used in alcohol tests. |
| -2 | Oxalate | $C_2O_4^{2-}$ | Causes kidney stones (Ca-oxalate). |
| -2 | Peroxide | $O_2^{2-}$ | Oxygen is -1 here. Unstable. |
| -3 | Phosphate | $PO_4^{3-}$ | Bio DNA/RNA/ATP backbone. |
| -3 | Phosphite | $PO_3^{3-}$ | One less oxygen than phosphate. |
| -3 | Arsenate | $AsO_4^{3-}$ | Toxic analog of phosphate. |
Advanced Inorganic Naming: Sophisticated rules for polyatomic ions and coordination complexes.
1.2 Variable Charge Metals (The "Stock System")
Many transition metals form multiple cations. The Stock System uses Roman Numerals to indicate charge. Older names (-ic/-ous) are less common but still tested.
Iron (Fe)
- $Fe^{2+}$ Iron(II) (Ferrous)
- $Fe^{3+}$ Iron(III) (Ferric)
Copper (Cu)
- $Cu^{+}$ Copper(I) (Cuprous)
- $Cu^{2+}$ Copper(II) (Cupric)
Tin (Sn) & Lead (Pb)
- $Sn^{2+}$ Tin(II) (Stannous)
- $Sn^{4+}$ Tin(IV) (Stannic)
- $Pb^{2+}$ Lead(II) (Plumbous)
1.3 Coordination Compounds (Complex Ions)
This is high-level material. Coordination compounds consist of a complex ion (metal + ligands) and counter-ions.
Naming Rules for Complexes
- Ligands First: Name ligands before the metal. Use prefixes (di-, tri-, tetra-) for the number of ligands.
- Ligand Names:
- Anionic ligands end in -o (Chloride → Chlorido/Chloro).
- Neutral ligands have specific names: Water → Aqua, Ammonia → Ammine (double m!), CO → Carbonyl.
- Metal Name:
- If the complex is a Cation (+): Use the metal name (Iron, Copper).
- If the complex is an Anion (-): Use the Latin root + -ate (Iron → Ferrate, Copper → Cuprate, Silver → Argentate).
- Oxidation State: Always indicate the metal's charge in Roman Numerals.
Tetraamminecopper(II) ion
Potassium hexacyanoferrate(II)
1.4 Hydrated Salts
Crystals containing specific amounts of water.
Convention:
[Salt Name] + [Greek Prefix]-hydrate
- $CuSO_4 \cdot 5H_2O$: Copper(II) sulfate pentahydrate (Blue)
- $MgSO_4 \cdot 7H_2O$: Magnesium sulfate heptahydrate (Epsom Salt)
- $CaSO_4 \cdot \frac{1}{2}H_2O$: Calcium sulfate hemihydrate (Plaster of Paris)
Challenge an IMAT Question!
Question 139 Official Paper: 2018 - Q42
worked solution & explanation
Concept Inorganic ion chemical formula.
Step 1 The fluoride ion is the monoatomic anion formed by fluorine.
Step 2 Fluorine is a halogen (Group VII) and gains 1 electron to achieve a noble gas configuration, forming $\text{F}^-$.
Part 2: Acid Nomenclature
Acids are generally divided into Binary Acids (H + Nonmetal) and Oxyacids (H + Polyatomic Oxygen Ion). Follow this flow:
2.1 Oxyacid Naming System
The name changes based on the oxidation state of the central atom (number of oxygens).
| Oxidation | Ref. Anion | Anion Name | Acid Name Rule | Example |
|---|---|---|---|---|
| Highest | $ClO_4^-$ | Per...ate | Per...ic acid | Perchloric acid |
| High | $ClO_3^-$ | ...ate | ...ic acid | Chloric acid |
| Low | $ClO_2^-$ | ...ite | ...ous acid | Chlorous acid |
| Lowest | $ClO^-$ | Hypo...ite | Hypo...ous acid | Hypochlorous acid |
Inorganic Oxyacid and Oxyanion Naming Rules: Visualizing the relationship between oxidation states, anion names, and acid names.
Challenge an IMAT Question!
Question 75 Official Paper: 2022 - Q52
worked solution & explanation
Concept Determining empirical formula from mass composition.
Step 1 Calculate moles of iron: $\text{Moles of Fe} = 1.68\text{ g} / 56\text{ g/mol} = 0.03\text{ mol}$.
Step 2 Calculate moles of oxygen: $\text{Moles of O} = 0.64\text{ g} / 16\text{ g/mol} = 0.04\text{ mol}$.
Step 3 Find the simplest integer ratio: $\text{Fe} : \text{O} = 0.03 : 0.04 = 3 : 4$, giving the empirical formula $\text{Fe}_3\text{O}_4$.
Part 3: Advanced IUPAC Organic Nomenclature
Organic naming is a puzzle. You must assemble the name from four parts: Locants - Prefixes - Parent - Suffix.
General Strategy for Complex Molecules
- Identify the Principal Functional Group: This determines the suffix (parent name) and the direction of numbering (it gets the lowest possible number).
- Find the Longest Carbon Chain: It must contain the principal functional group and maximum number of multiple bonds, even if a longer chain exists without them.
- Number the Chain: Give the Principal Group the lowest number. If there is no principal group, minimize the numbers of substituents.
- Assemble Substituents: List them alphabetically (ethyl before methyl). Ignore prefixes like di-, tri-, sec-, tert- for alphabetizing, but include iso-.
3.1 Updated Priority Table (High Yield)
Memorize this exact order. Higher on list = Suffix. Lower on list = Prefix.
Organic Priority Hierarchy Pyramid: A definitive priority decision ladder for functional groups.
| Priority | Class | Formula | Suffix (Parent) | Prefix (Substituent) |
|---|---|---|---|---|
| 1 | Carboxylic Acid | -COOH | -oic acid | Carboxy- |
| 2 | Ester | -COOR | -oate | (alkoxycarbonyl-) |
| 3 | Acyl Halide | -COX | -oyl halide | Haloformyl- |
| 4 | Amide | -CONH₂ | -amide | Carbamoyl- |
| 5 | Nitrile | -CN | -nitrile | Cyano- |
| 6 | Aldehyde | -CHO | -al | Formyl- / Oxo- |
| 7 | Ketone | -CO- | -one | Oxo- |
| 8 | Alcohol | -OH | -ol | Hydroxy- |
| 9 | Thiol | -SH | -thiol | Mercapto- |
| 10 | Amine | -NH₂ | -amine | Amino- |
| 11 | Alkene | -C=C- | -ene | Alkenyl- |
| 12 | Alkyne | -C≡C- | -yne | Alkynyl- |
| 13 | Ether | -OR | (None) | Alkoxy- |
| 14 | Nitro | -NO₂ | (None) | Nitro- |
| 15 | Halogen | -X | (None) | Halo- (Fluoro, Chloro...) |
3.2 Specific Functional Group Rules
Esters (-COOR)
Named as salts of carboxylic acids. Alkyl group on Oxygen first.
1. Group on O: Methyl
2. Acid (3C): Propanoate
Methyl propanoate
Amides (-CONH₂)
Substituents on Nitrogen use locant N-.
1. Parent (2C): Ethanamide
2. On N: Methyl, Ethyl
N-ethyl-N-methylethanamide
3.3 Cyclic Compounds
For cyclic alkanes, add the prefix cyclo-. Number the ring to give substituents the lowest set of locants.
Cyclic & Aromatic Grammar: Contrasting cycloalkane substituent numbering and benzene ortho-, meta-, para- rules.
Challenge an IMAT Question!
Question 76 Official Paper: 2019 - Q44
worked solution & explanation
Concept Empirical formula from mass composition.
Step 1 Mass of compound = $8\text{ g}$. Carbon = $3\text{ g}$, Hydrogen = $1\text{ g}$. The remaining mass must be Oxygen: $\text{Oxygen} = 8 - (3 + 1) = 4\text{ g}$.
Step 2 Calculate moles: $\text{C} = 3/12 = 0.25\text{ mol}$, $\text{H} = 1/1 = 1.0\text{ mol}$, $\text{O} = 4/16 = 0.25\text{ mol}$.
Step 3 The mole ratio is $\text{C} : \text{H} : \text{O} = 0.25 : 1.0 : 0.25 = 1 : 4 : 1$. The empirical formula is $\text{CH}_4\text{O}$, which matches methanol (Option E).
Part 4: Stereochemistry & Isomerism Hierarchy
Isomerism is a major topic in IMAT. Understand the hierarchy.
Isomers: A comprehensive visualization of the isomerism hierarchy, from structural to stereoisomers.
4.1 Naming Stereoisomers
Alkenes: E/Z System
Used when cis/trans is ambiguous (more than 2 substituents).
High priority groups on
SAME side.
"Zame Zide"
High priority groups on
OPPOSITE side.
"Epposite"
Chiral Centers: R/S Configuration
1. Assign priority (1-4) based on Atomic Number (Cahn-Ingold-Prelog).
2. Point lowest priority group (4) AWAY.
- 1 → 2 → 3 is Clockwise = R (Rectus/Right)
- 1 → 2 → 3 is Counter-Clockwise = S (Sinister/Left)
Deep Dive Stereoisomer Naming: Advanced instructional chart for E/Z geometric isomerism and R/S optical isomerism configurations.
Challenge an IMAT Question!
Question 155 Official Paper: 2019 - Q41
worked solution & explanation
Concept Quantum mechanical definition of atomic orbitals.
Step 1 According to the quantum mechanical model of the atom, electrons do not travel in defined planetary orbits.
Step 2 An atomic orbital is a mathematical description of the region of space surrounding the nucleus where there is a high probability of finding the electron.
Part 5: The Great Library of Compounds
Below are lists of compounds you should recognize instantly. This section is expanded to include medical relevance.
5.1 Medical & Biological Compounds
| Common Name | IUPAC / Systematic Name | Structure/Notes |
|---|---|---|
| Aspirin | Acetylsalicylic acid | 2-acetoxybenzoic acid. Analgesic. |
| Paracetamol | Acetaminophen (US) | N-(4-hydroxyphenyl)acetamide. |
| Lactic Acid | 2-Hydroxypropanoic acid | Produced in muscles anaerobically. |
| Pyruvic Acid | 2-Oxopropanoic acid | End product of glycolysis. |
| Glycerol | Propane-1,2,3-triol | Backbone of triglycerides. |
| Glycine | Aminoethanoic acid | Simplest amino acid (not chiral). |
| Alanine | 2-Aminopropanoic acid | Simple chiral amino acid. |
| Urea | Diaminomethanal | Nitrogen waste product. |
5.2 Common Organic Names (Crucial for IMAT)
| Common Name | IUPAC / Structure | Class |
|---|---|---|
| Formic Acid | Methanoic Acid (HCOOH) | Carboxylic Acid (Ants) |
| Acetic Acid | Ethanoic Acid (CH₃COOH) | Carboxylic Acid (Vinegar) |
| Propionic Acid | Propanoic Acid | Carboxylic Acid |
| Butyric Acid | Butanoic Acid | Carboxylic Acid (Butter) |
| Valeric Acid | Pentanoic Acid | Carboxylic Acid |
| Oxalic Acid | Ethanedioic acid | 2 Carbons |
| Malonic Acid | Propanedioic acid | 3 Carbons |
| Succinic Acid | Butanedioic acid | 4 Carbons |
| Glutaric Acid | Pentanedioic acid | 5 Carbons |
| Formaldehyde | Methanal (HCHO) | Preservative |
| Acetaldehyde | Ethanal (CH₃CHO) | Hangover cause |
| Acetone | Propanone | Solvent |
| Acetophenone | 1-Phenylethanone | Aromatic Ketone |
| Benzophenone | Diphenylmethanone | Aromatic Ketone |
| Toluene | Methylbenzene | Solvent |
| Phenol | Hydroxybenzene | Antiseptic |
| Aniline | Aminobenzene | Dyes |
| Anisole | Methoxybenzene | Perfumes |
| Styrene | Vinylbenzene | Polystyrene |
| Cumene | Isopropylbenzene | Precursor to phenol |
| Benzoic Acid | Benzenecarboxylic acid | Preservative |
| Benzaldehyde | Benzenecarbaldehyde | Almond smell |
Organized Library: A powerful high-yield reference for common and trivial names encountered in biology and medicine.
Challenge an IMAT Question!
Question 159 Official Paper: 2015 - Q50
worked solution & explanation
Concept Molarity calculations.
Step 1 Molarity ($M$) is defined as the moles of solute per liter of solution ($M = \text{moles} / V$).
Step 2 Rearranging the formula to find volume: $V = \text{moles} / M$.
Step 3 Calculate: $V = 0.1\text{ moles} / 0.1\text{ M} = 1\text{ L}$.
Interactive Master Quiz
Test your mastery of advanced chemical nomenclature. Pay attention to oxidation states and priority rules.